《纺织复合材料》课程参考文献（Composite Materials Handbook，Volume 1）CHAPTER 4 MATRIX CHARACTERIZATION

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization CHAPTER 4 MATRIX CHARACTERIZATION 4.1 INTRODUCTION The function of the matrix in a composite is to hold the fibers in the desired position,and to provide a path for introducing external loads into the fibers.Since the strengths of matrix materials are generally lower than fiber strengths by an order of magnitude or more,it is desirable to orient the fibers within a composite structure so that they will carry the major external loads.Although the success of composites is largely due to this ability,the strength and other properties of matrix materials cannot be ignored.Ma- trix material properties can significantly affect how a composite will perform,particularly with respect to in- plane compression,in-plane shear,resistance to impact damage,and other interlaminar behavior,and especially when exposed to moisture and elevated temperatures. A wide range of polymeric resin systems are used as the matrix portion of fiber reinforced compos- ites.These systems generally fall into two broad categories:thermoplastic materials and thermosetting materials.The thermoplastics are non-reactive solids designed to soften,melt,and intimately infiltrate reinforcement fiber bundles at appropriate processing temperatures and pressures,and to solidify into a desired shape upon cooling.Thermosets are reactive materials comprised of organic resins and other constituents required for chemical "curing."They may exist in various forms(liquid,solid,film,powder, pellets,etc.)in the uncured state,and may be partially reacted prior to combining with the reinforcing fi- bers.During composite processing they react irreversibly to form solids.In addition to the organic con- stituents,thermoset systems may also contain additives such as catalysts,fillers,and processing aids, which may be inorganic or contain metals.Thermoplastic or elastomeric fillers may also be incorporated. Due to their reactive nature,most uncured thermosets must be stored under refrigeration,although some multi-part systems designed for component mixing just prior to use may not require cold storage.Both thermoplastics and thermosets can be used to preimpregnate reinforcing fibers to produce prepreg,while processes like RTM(resin transfer molding)are generally more suited to thermosets. This chapter focuses on methods of testing and characterizing matrix materials and their constituents. Chemical,physical,thermal,and mechanical properties are considered,as well as methods for test specimen preparation and environmental conditioning of test specimens.Tests of thermosets(in both the cured and uncured states),and thermoplastics are addressed. The properties covered in this chapter will largely be of interest to resin formulators and material sup- pliers.The composite end user will also find some matrix properties useful,particularly for process cycle development and,to a lesser extent,for initial screening and material selection.A number of matrix prop- erties and tests are also applicable to quality assurance,especially if resins are purchased separately from the reinforcement for use in RTM or similar processes. 4.2 MATRIX SPECIMEN PREPARATION 4.2.1 Introduction Specimens of unreinforced(neat)matrix material are required for physical and/or mechanical charac- terization of these polymers in the solid (cured)state.Methods available for specimen preparation are strongly dictated by the type of matrix material being studied.Primary variables include thermoset vs thermoplastic,viscosity at various processing stages,processing temperature,amount of volatiles evolved,and degree of brittleness in the fabricated state.When working with uncured polymers,personal safety is always a concern,and the appropriate Material Safety Data Sheets (MSDS)should be con- sulted. 4-1

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-1 CHAPTER 4 MATRIX CHARACTERIZATION 4.1 INTRODUCTION The function of the matrix in a composite is to hold the fibers in the desired position, and to provide a path for introducing external loads into the fibers. Since the strengths of matrix materials are generally lower than fiber strengths by an order of magnitude or more, it is desirable to orient the fibers within a composite structure so that they will carry the major external loads. Although the success of composites is largely due to this ability, the strength and other properties of matrix materials cannot be ignored. Ma￾trix material properties can significantly affect how a composite will perform, particularly with respect to in￾plane compression, in-plane shear, resistance to impact damage, and other interlaminar behavior, and especially when exposed to moisture and elevated temperatures. A wide range of polymeric resin systems are used as the matrix portion of fiber reinforced compos￾ites. These systems generally fall into two broad categories: thermoplastic materials and thermosetting materials. The thermoplastics are non-reactive solids designed to soften, melt, and intimately infiltrate reinforcement fiber bundles at appropriate processing temperatures and pressures, and to solidify into a desired shape upon cooling. Thermosets are reactive materials comprised of organic resins and other constituents required for chemical “curing.” They may exist in various forms (liquid, solid, film, powder, pellets, etc.) in the uncured state, and may be partially reacted prior to combining with the reinforcing fi￾bers. During composite processing they react irreversibly to form solids. In addition to the organic con￾stituents, thermoset systems may also contain additives such as catalysts, fillers, and processing aids, which may be inorganic or contain metals. Thermoplastic or elastomeric fillers may also be incorporated. Due to their reactive nature, most uncured thermosets must be stored under refrigeration, although some multi-part systems designed for component mixing just prior to use may not require cold storage. Both thermoplastics and thermosets can be used to preimpregnate reinforcing fibers to produce prepreg, while processes like RTM (resin transfer molding) are generally more suited to thermosets. This chapter focuses on methods of testing and characterizing matrix materials and their constituents. Chemical, physical, thermal, and mechanical properties are considered, as well as methods for test specimen preparation and environmental conditioning of test specimens. Tests of thermosets (in both the cured and uncured states), and thermoplastics are addressed. The properties covered in this chapter will largely be of interest to resin formulators and material sup￾pliers. The composite end user will also find some matrix properties useful, particularly for process cycle development and, to a lesser extent, for initial screening and material selection. A number of matrix prop￾erties and tests are also applicable to quality assurance, especially if resins are purchased separately from the reinforcement for use in RTM or similar processes. 4.2 MATRIX SPECIMEN PREPARATION 4.2.1 Introduction Specimens of unreinforced (neat) matrix material are required for physical and/or mechanical charac￾terization of these polymers in the solid (cured) state. Methods available for specimen preparation are strongly dictated by the type of matrix material being studied. Primary variables include thermoset vs thermoplastic, viscosity at various processing stages, processing temperature, amount of volatiles evolved, and degree of brittleness in the fabricated state. When working with uncured polymers, personal safety is always a concern, and the appropriate Material Safety Data Sheets (MSDS) should be con￾sulted

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization 4.2.2 Thermoset polymers Thermoset polymers of interest,i.e.,those used as matrices in composites,are typically of sufficiently low viscosity at some point during the cure process to flow.Thus,they may be cast into plate forms to provide blanks from which finished specimens can be machined,or molded into even more complex ge- ometries if necessary to create net-dimension specimens directly. When casting neat(unreinforced)polymers for use as mechanical test specimens,it is critical that voids,inclusions,and similar defects be minimized,both in size and number.Most thermoset polymers used as matrices,even those considered to be toughened,tend to be relatively brittle,and thus their ulti- mate strengths are strongly dictated by critical flaw size. Inclusions can be present in impure resin as obtained from the supplier,or introduced during the fab- rication process (e.g.,inadequately cleaned molds,airborne dirt particles,inadequate mixing of compo- nents,etc.).Caution also must be exercised when using release agents,to avoid contamination of the polymer. Defects can be in the form of surface scratches,edge chips,and mold marks.Voids are typically caused by trapped volatiles which evolve during the initial stages of the curing process.The evolution of volatiles can be suppressed,or at least minimized,by subjecting the polymer to pressure during the cur- ing process.However,it is more common to apply a vacuum during the initial stage of the cure cycle, either while the polymer is still in the mixing container or already in the mold.This is done at one or more points in time as the temperature is being elevated,and while the viscosity is at its lowest.Thus,a vac- uum oven is useful. The vacuum can evoke a strong evolution of volatiles,requiring that the container or mold have suffi- cient volume to contain the frothy polymer until the gas bubbles burst.If a single flat panel is to be fabri- cated,a simple box mold consisting of five steel plates,viz.,a bottom and four sufficiently high sides,held together with screws,works well.This box can be disassembled after cure,for ease of polymer matrix plate removal,and easy clean-up.Individual strips of polymer can also be made in this manner,by plac- ing thin steel strips of width equal to the desired polymer matrix specimen width upright on one long edge, spaced apart to the desired polymer specimen thickness. Since volatiles are being evacuated,the vacuum pump itself should be protected,by the use of a cold trap to condense these vapors before they pass through the pump. If a cavity mold is being used to produce individual specimens of net dimensions,an elastomeric fun- nel works well to contain the volume of volatiles;the polymer will flow back down into the mold as the bubbles collapse.The funnel can then be left in place during the remainder of the cure.During clean-up, the funnel can be flexed to easily remove the cured polymer residue on it. The individual specimen cavity molds can be fabricated of metal,usually steel rather than aluminum because of its lower thermal expansion and higher surface hardness.These are typically two-piece split molds,to permit cured specimen removal.Elastomeric molds,themselves easily fabricated by casting around a permanent pattern,are an attractive alternative.The cured mold can be slit along its length to remove it from around the pattern,this slit also permitting it to be later pried open to easily remove the polymer specimen cast in it.In any case,the individual specimen molds are typically ganged together for efficiency.The as-molded specimens are ready for testing with little or no further preparation.At most, and primarily for aesthetic reasons,the mold seam(s)may be lightly sanded off. If vacuum is not being subsequently used to remove volatiles,the molds can be filled from the bot- tom,to minimize trapped air,but this adds complication and is usually not necessary.Likewise,if the vis- cosity of the polymer is too high for gravity fill,pressure can be used to force it into the mold.Again,this is not usually necessary considering the composite processing requirements of these polymers as matrix materials anyway. 4-2

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-2 4.2.2 Thermoset polymers Thermoset polymers of interest, i.e., those used as matrices in composites, are typically of sufficiently low viscosity at some point during the cure process to flow. Thus, they may be cast into plate forms to provide blanks from which finished specimens can be machined, or molded into even more complex ge￾ometries if necessary to create net- dimension specimens directly. When casting neat (unreinforced) polymers for use as mechanical test specimens, it is critical that voids, inclusions, and similar defects be minimized, both in size and number. Most thermoset polymers used as matrices, even those considered to be toughened, tend to be relatively brittle, and thus their ulti￾mate strengths are strongly dictated by critical flaw size. Inclusions can be present in impure resin as obtained from the supplier, or introduced during the fab￾rication process (e.g., inadequately cleaned molds, airborne dirt particles, inadequate mixing of compo￾nents, etc.). Caution also must be exercised when using release agents, to avoid contamination of the polymer. Defects can be in the form of surface scratches, edge chips, and mold marks. Voids are typically caused by trapped volatiles which evolve during the initial stages of the curing process. The evolution of volatiles can be suppressed, or at least minimized, by subjecting the polymer to pressure during the cur￾ing process. However, it is more common to apply a vacuum during the initial stage of the cure cycle, either while the polymer is still in the mixing container or already in the mold. This is done at one or more points in time as the temperature is being elevated, and while the viscosity is at its lowest. Thus, a vac￾uum oven is useful. The vacuum can evoke a strong evolution of volatiles, requiring that the container or mold have suffi￾cient volume to contain the frothy polymer until the gas bubbles burst. If a single flat panel is to be fabri￾cated, a simple box mold consisting of five steel plates, viz., a bottom and four sufficiently high sides, held together with screws, works well. This box can be disassembled after cure, for ease of polymer matrix plate removal, and easy clean-up. Individual strips of polymer can also be made in this manner, by plac￾ing thin steel strips of width equal to the desired polymer matrix specimen width upright on one long edge, spaced apart to the desired polymer specimen thickness. Since volatiles are being evacuated, the vacuum pump itself should be protected, by the use of a cold trap to condense these vapors before they pass through the pump. If a cavity mold is being used to produce individual specimens of net dimensions, an elastomeric fun￾nel works well to contain the volume of volatiles; the polymer will flow back down into the mold as the bubbles collapse. The funnel can then be left in place during the remainder of the cure. During clean-up, the funnel can be flexed to easily remove the cured polymer residue on it. The individual specimen cavity molds can be fabricated of metal, usually steel rather than aluminum because of its lower thermal expansion and higher surface hardness. These are typically two-piece split molds, to permit cured specimen removal. Elastomeric molds, themselves easily fabricated by casting around a permanent pattern, are an attractive alternative. The cured mold can be slit along its length to remove it from around the pattern, this slit also permitting it to be later pried open to easily remove the polymer specimen cast in it. In any case, the individual specimen molds are typically ganged together for efficiency. The as-molded specimens are ready for testing with little or no further preparation. At most, and primarily for aesthetic reasons, the mold seam(s) may be lightly sanded off. If vacuum is not being subsequently used to remove volatiles, the molds can be filled from the bot￾tom, to minimize trapped air, but this adds complication and is usually not necessary. Likewise, if the vis￾cosity of the polymer is too high for gravity fill, pressure can be used to force it into the mold. Again, this is not usually necessary considering the composite processing requirements of these polymers as matrix materials anyway

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization As an alternative to a box mold for fabricating flat neat matrix plates,the polymer can be cast be- tween two vertically positioned flat plates,held the desired cast polymer plate thickness apart by spacers, and sealed around three edges.The polymer is then poured into the open top edge.The plates may be metal or glass.However,this technique is not always successful.Because of the constraint of the mold at both surfaces of the polymer,and the difficulty of achieving full release,the cast polymer plate may crack due to the stresses induced by differential thermal contraction during cooldown from the cure tem- perature.Also,the polymer,which typically has a higher coefficient of thermal expansion than the mold, may contract away from the mold surfaces,producing a mottled surface.These local depressions are typically very shallow and can be removed by subsequent surface grinding of the cast plate.However, thermal residual strains associated with the formation of these surface irregularities remain (as can be observed under polarized light),and are very difficult to anneal out.Also,the very long path length that any trapped air bubbles or volatiles must travel to reach the free surface makes the production of void- free polymer plates more difficult to achieve. 4.2.3 Thermoplastic polymers Thermoplastic polymers used in composites are typically high processing temperature (620-840F (325-450C))systems and higher temperature mold materials must be used.Matrix polymers for use in fabricating neat specimens tend to be available in film or granular forms.Pressure injection or compac- tion is typically necessary,which is complicated by the fact that the minimum viscosities achievable tend to be higher than for thermosets.Although volatile evolution is usually not an issue when molding ther- moplastics since they are typically fully polymerized,trapped air can still be a problem.Thus,the use of vacuum during forming may still be desirable. These high temperature thermoplastics tend to be less brittle than the thermoset polymer matrix ma- terials.Thus,cracking of the polymer plate during the molding operation due to differential contraction of plate and mold is less of a problem,but it can still occur. 4.2.4 Specimen machining For both thermosets and thermoplastics,if the neat matrix specimen has been molded to final shape. no additional preparation is needed.Dogbone cylindrical specimens,typically for use in solid-rod torsion testing,but sometimes used for tension and compression testing,are one such example. Tension,compression,and losipescu shear specimens of thermoset polymers are typically machined from flat plates or strips rather than being molded to net dimensions.Although individual dogbone flat specimens of commodity thermoplastics are commonly (injection-)molded to final dimensions,high tem- perature thermoplastic matrix materials are usually not.Rather,flat rectangular blanks are molded,and dogbone specimens are machined from them. The various polymers are relatively easy to machine using abrasive wheels.If desired,the surfaces of as-molded plates can be ground prior to cutting individual specimens from them.The plates are cut into strips and specimen blanks using thin abrasive blades,although sometimes diamond wheels,or even toothed band saw blades,are used.Dogbone specimens can then be ground to final dimensions.The notches in losipescu shear specimens can likewise be ground in,using shaped grinding wheels and mul- tiple passes.Specimens can be stacked together for this operation,mutually supporting each other. Most polymer matrix specimens will tolerate minor grinding-induced scratches and chipped edges, even though this is never desirable.However,some polymers are extremely sensitive to these surface defects.All surfaces and edges within the specimen gage length must then be carefully smoothed with fine (e.g.,down to 600-grit)emery cloth.When working with a new polymer matrix,both as-ground and surface-polished tensile specimens should initially be tested,to determine the polymer's sensitivity to sur- face defects.Since final polishing adds additional labor cost,it is desirable to only do so when necessary. 4-3

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-3 As an alternative to a box mold for fabricating flat neat matrix plates, the polymer can be cast be￾tween two vertically positioned flat plates, held the desired cast polymer plate thickness apart by spacers, and sealed around three edges. The polymer is then poured into the open top edge. The plates may be metal or glass. However, this technique is not always successful. Because of the constraint of the mold at both surfaces of the polymer, and the difficulty of achieving full release, the cast polymer plate may crack due to the stresses induced by differential thermal contraction during cooldown from the cure tem￾perature. Also, the polymer, which typically has a higher coefficient of thermal expansion than the mold, may contract away from the mold surfaces, producing a mottled surface. These local depressions are typically very shallow and can be removed by subsequent surface grinding of the cast plate. However, thermal residual strains associated with the formation of these surface irregularities remain (as can be observed under polarized light), and are very difficult to anneal out. Also, the very long path length that any trapped air bubbles or volatiles must travel to reach the free surface makes the production of void￾free polymer plates more difficult to achieve. 4.2.3 Thermoplastic polymers Thermoplastic polymers used in composites are typically high processing temperature (620-840°F (325-450°C)) systems and higher temperature mold materials must be used. Matrix polymers for use in fabricating neat specimens tend to be available in film or granular forms. Pressure injection or compac￾tion is typically necessary, which is complicated by the fact that the minimum viscosities achievable tend to be higher than for thermosets. Although volatile evolution is usually not an issue when molding ther￾moplastics since they are typically fully polymerized, trapped air can still be a problem. Thus, the use of vacuum during forming may still be desirable. These high temperature thermoplastics tend to be less brittle than the thermoset polymer matrix ma￾terials. Thus, cracking of the polymer plate during the molding operation due to differential contraction of plate and mold is less of a problem, but it can still occur. 4.2.4 Specimen machining For both thermosets and thermoplastics, if the neat matrix specimen has been molded to final shape, no additional preparation is needed. Dogbone cylindrical specimens, typically for use in solid-rod torsion testing, but sometimes used for tension and compression testing, are one such example. Tension, compression, and Iosipescu shear specimens of thermoset polymers are typically machined from flat plates or strips rather than being molded to net dimensions. Although individual dogbone flat specimens of commodity thermoplastics are commonly (injection-) molded to final dimensions, high tem￾perature thermoplastic matrix materials are usually not. Rather, flat rectangular blanks are molded, and dogbone specimens are machined from them. The various polymers are relatively easy to machine using abrasive wheels. If desired, the surfaces of as-molded plates can be ground prior to cutting individual specimens from them. The plates are cut into strips and specimen blanks using thin abrasive blades, although sometimes diamond wheels, or even toothed band saw blades, are used. Dogbone specimens can then be ground to final dimensions. The notches in Iosipescu shear specimens can likewise be ground in, using shaped grinding wheels and mul￾tiple passes. Specimens can be stacked together for this operation, mutually supporting each other. Most polymer matrix specimens will tolerate minor grinding-induced scratches and chipped edges, even though this is never desirable. However, some polymers are extremely sensitive to these surface defects. All surfaces and edges within the specimen gage length must then be carefully smoothed with fine (e.g., down to 600-grit) emery cloth. When working with a new polymer matrix, both as-ground and surface-polished tensile specimens should initially be tested, to determine the polymer's sensitivity to sur￾face defects. Since final polishing adds additional labor cost, it is desirable to only do so when necessary

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization 4.3 CONDITIONING AND ENVIRONMENTAL EXPOSURE These issues as applied to the matrix materials themselves(after cure or consolidation)are very simi- lar to the same issues applied to the composite materials using these matrices.The latter case is dis- cussed in detail in Volume 1,Section 6.3.Despite this there are several distinct differences that affect how the information in Section 6.3 is applied to unreinforced matrix material.These include the following: 1.Without reinforcement,most matrix materials are nearly isotropic.In such cases,conditioning re- strictions or concerns based on consideration of anisotropy,such as specimen aspect ratio con- cerns due to moisture absorption through the edge of a specimen,need no longer apply. 2. The transport properties (thermal and moisture)of the unreinforced matrix materials are signifi- cantly different than those of the composite.For example,an unreinforced ("neat")epoxy has both a significantly higher diffusivity constant and a significantly higher equilibrium moisture con- tent,as compared to a fiber reinforced composite containing the same resin system. 3.Additional test methods for properties of the matrix material are available that are not typically applied to the composite,such as the moisture content test methods for matrix materials dis- cussed in Section 4.5.7. 4.4 CHEMICAL ANALYSIS TECHNIQUES Chemical characterization techniques are listed in Table 4.4.Elemental analysis and functional group analysis provide basic and quantitative information relating to chemical composition.Spectroscopic analy- sis provides detailed information about molecular structure,conformation,morphology,and physical- chemical characteristics of polymers.Chromatographic techniques separate sample components from one another,and thereby simplify compositional characterization and make a more accurate analysis possible.Employing spectroscopic techniques to monitor components separated by gas or liquid chroma- tography greatly enhances characterization,providing a means to identify and quantitatively analyze even the most minor components. 4.4.1 Elemental analysis Elemental analysis techniques such as ion chromatography,atomic absorption(AA),X-ray fluores- cence,or emission spectroscopy can be applied to analyze specific elements,such as boron or fluorine When necessary,X-ray diffraction may also be used to identify crystalline components,such as fillers, and to determine the relative percent crystallinity for certain resins. 4.4.2 Functional group and wet chemical analysis The analysis of reactive functional groups is particularly important in determining equivalent weights of prepolymers.Titration and wet chemical analysis for specific functional groups are useful techniques for characterizing individual epoxy components but have limited application and may provide misleading results when complex resin formulations are analyzed. 4.4.3 Spectroscopic analysis Infrared spectroscopy (IRS)provides more useful information for identifying polymers and polymer precursors than any other absorption or vibrational spectroscopy technique and is generally available in most laboratories.IR yields both qualitative and quantitative information concerning a polymer sample's chemical nature,i.e.,structural repeat units,end groups and branch units,additives and impurities(Ref- erence 4.4.3(a)).Computerized libraries of spectra for common polymeric materials exist for direct com- parison and identification of unknowns.Computer software allows the spectrum of a standard polymer to be subtracted from an unknown to estimate its concentration and perhaps to determine whether another type of polymer is also present in the sample. 4-4

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-4 4.3 CONDITIONING AND ENVIRONMENTAL EXPOSURE These issues as applied to the matrix materials themselves (after cure or consolidation) are very simi￾lar to the same issues applied to the composite materials using these matrices. The latter case is dis￾cussed in detail in Volume 1, Section 6.3. Despite this there are several distinct differences that affect how the information in Section 6.3 is applied to unreinforced matrix material. These include the following: 1. Without reinforcement, most matrix materials are nearly isotropic. In such cases, conditioning re￾strictions or concerns based on consideration of anisotropy, such as specimen aspect ratio con￾cerns due to moisture absorption through the edge of a specimen, need no longer apply. 2. The transport properties (thermal and moisture) of the unreinforced matrix materials are signifi￾cantly different than those of the composite. For example, an unreinforced ("neat") epoxy has both a significantly higher diffusivity constant and a significantly higher equilibrium moisture con￾tent, as compared to a fiber reinforced composite containing the same resin system. 3. Additional test methods for properties of the matrix material are available that are not typically applied to the composite, such as the moisture content test methods for matrix materials dis￾cussed in Section 4.5.7. 4.4 CHEMICAL ANALYSIS TECHNIQUES Chemical characterization techniques are listed in Table 4.4. Elemental analysis and functional group analysis provide basic and quantitative information relating to chemical composition. Spectroscopic analy￾sis provides detailed information about molecular structure, conformation, morphology, and physical￾chemical characteristics of polymers. Chromatographic techniques separate sample components from one another, and thereby simplify compositional characterization and make a more accurate analysis possible. Employing spectroscopic techniques to monitor components separated by gas or liquid chroma￾tography greatly enhances characterization, providing a means to identify and quantitatively analyze even the most minor components. 4.4.1 Elemental analysis Elemental analysis techniques such as ion chromatography, atomic absorption (AA), X-ray fluores￾cence, or emission spectroscopy can be applied to analyze specific elements, such as boron or fluorine. When necessary, X-ray diffraction may also be used to identify crystalline components, such as fillers, and to determine the relative percent crystallinity for certain resins. 4.4.2 Functional group and wet chemical analysis The analysis of reactive functional groups is particularly important in determining equivalent weights of prepolymers. Titration and wet chemical analysis for specific functional groups are useful techniques for characterizing individual epoxy components but have limited application and may provide misleading results when complex resin formulations are analyzed. 4.4.3 Spectroscopic analysis Infrared spectroscopy (IRS) provides more useful information for identifying polymers and polymer precursors than any other absorption or vibrational spectroscopy technique and is generally available in most laboratories. IR yields both qualitative and quantitative information concerning a polymer sample's chemical nature, i.e., structural repeat units, end groups and branch units, additives and impurities (Ref￾erence 4.4.3(a)). Computerized libraries of spectra for common polymeric materials exist for direct com￾parison and identification of unknowns. Computer software allows the spectrum of a standard polymer to be subtracted from an unknown to estimate its concentration and perhaps to determine whether another type of polymer is also present in the sample

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization TABLE 4.4 Techniques for chemical characterization. Elemental Analysis- Conventional Analytical Techniques X-Ray Fluorescence Atomic Absorption(AA) ICAP EDAX Neutron Activation Analysis Functional Group Analysis- Conventional Wet Chemical Techniques Potentiometric Titration Coulometry Radiography Spectroscopic Analysis- Infrared(Pellet,Film,Dispersion,Reflectance),Fourier Transform IR (FTIR),Photoacoustic FTIR,Internal Reflection IR,IR Micros- copy,Dichroism Laser Raman Nuclear Magnetic Resonance (NMR)13C,1H,15N;Conventional (Soluble Sample).Solid State (Machined or Molded Sample) Fluorescence,Chemiluminescence,Phosphorescence Ultraviolet-Visible (UV-VIS) Mass Spectroscopy(MS),Election Impact MS,Field Desorption MS. Laser Desorption MS,Secondary lon Mass Spectroscopy(SIMS). Chemical lonization MS Electron Spin Resonance(ESR) ESCA(Electron Spectroscopy for Chemical Analysis) X-Ray Photoelectron X-Ray Emission X-Ray Scattering(Small Angle-Saxs) Small-Angle Neutron Scattering(SANS) Dynamic Light Scattering Chromatographic Analysis- Gas Chromatography(GC)or GC/MS(Low MW Compounds) Pyrolysis-GC and GC/MS(Pyrolysis Products) Headspace GC/MS (Volatiles) Inverse GC (Thermodynamic Interaction Parameters) Size-Exclusion Chromatography(SEC),SEC-IR Liquid Chromatography (LC or HPLC),HPLC-MS,Multi-Dimensional/ Orthogonal LC,Microbore LC Supercritical Fluid Chromatography(SFC) Thin-Layer Chromatography(TLC),2-D TLC Infrared(IR)spectroscopy is sensitive to changes in the dipole moments of vibrating groups in mole- cules and,accordingly,yields useful information for the identification of resin components.IR spectros- copy provides a fingerprint of the resin composition and is not limited by the solubility of resin components (References 4.4.3(b)-4.4.3(d)).Indeed,gases,liquids and solids may be analyzed by IR spectroscopy. Advances in technology have led to the development of Fourier transform infrared spectroscopy(FTIR),a computer-supported IR technique for rapidly scanning and storing infrared spectra.Multiple scans and Fourier transformation of the infrared spectra enhance the signal-to-noise ratio and provide improved 4-5

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-5 TABLE 4.4 Techniques for chemical characterization. Elemental Analysis - Conventional Analytical Techniques X-Ray Fluorescence Atomic Absorption (AA) ICAP EDAX Neutron Activation Analysis Functional Group Analysis - Conventional Wet Chemical Techniques Potentiometric Titration Coulometry Radiography Spectroscopic Analysis - Infrared (Pellet, Film, Dispersion, Reflectance), Fourier Transform IR (FTIR), Photoacoustic FTIR, Internal Reflection IR, IR Micros￾copy, Dichroism Laser Raman Nuclear Magnetic Resonance (NMR) 13C, 1H, 15N; Conventional (Soluble Sample), Solid State (Machined or Molded Sample) Fluorescence, Chemiluminescence, Phosphorescence Ultraviolet-Visible (UV-VIS) Mass Spectroscopy (MS), Election Impact MS, Field Desorption MS, Laser Desorption MS, Secondary Ion Mass Spectroscopy (SIMS), Chemical Ionization MS Electron Spin Resonance (ESR) ESCA (Electron Spectroscopy for Chemical Analysis) X-Ray Photoelectron X-Ray Emission X-Ray Scattering (Small Angle-Saxs) Small-Angle Neutron Scattering (SANS) Dynamic Light Scattering Chromatographic Analysis - Gas Chromatography (GC) or GC/MS (Low MW Compounds) Pyrolysis-GC and GC/MS (Pyrolysis Products) Headspace GC/MS (Volatiles) Inverse GC (Thermodynamic Interaction Parameters) Size-Exclusion Chromatography (SEC), SEC-IR Liquid Chromatography (LC or HPLC), HPLC-MS, Multi-Dimensional/ Orthogonal LC, Microbore LC Supercritical Fluid Chromatography (SFC) Thin-Layer Chromatography (TLC), 2-D TLC Infrared (IR) spectroscopy is sensitive to changes in the dipole moments of vibrating groups in mole￾cules and, accordingly, yields useful information for the identification of resin components. IR spectros￾copy provides a fingerprint of the resin composition and is not limited by the solubility of resin components (References 4.4.3(b) - 4.4.3(d)). Indeed, gases, liquids and solids may be analyzed by IR spectroscopy. Advances in technology have led to the development of Fourier transform infrared spectroscopy (FTIR), a computer-supported IR technique for rapidly scanning and storing infrared spectra. Multiple scans and Fourier transformation of the infrared spectra enhance the signal-to-noise ratio and provide improved

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization spectra for interpretation.In addition.the FTIR attenuated total reflection (ATR)and diffuse reflectance techniques may be applied for quality assurance of thermoset composite materials to assess their state of cure;i.e.,residual epoxide concentration.(See Section 5.5.3) Although not as popular as IR,laser Raman spectroscopy complements IR as an identification tech- nique and is relatively simple to apply(Reference 4.4.3(a)).As long as the specimen is stable to the high intensity incident light and does not contain species that fluoresce,little or no sample preparation is nec- essary.Solid specimens need only be cut to fit into the sample holder.Transmission spectra are obtained directly with transparent specimens.For translucent specimens,a hole may be drilled into the specimen for passage of the incident light and a transmission spectra obtained by analyzing light scattered perpen- dicular to the incident beam.The spectrum of a turbid or highly scattering specimen is obtained by ana- lyzing the light reflected from its front surface.Powdered samples are simply tamped into a transparent glass tube and fibers can be oriented in the path of the incident beam for direct analysis. 4.4.4 Chromatographic analysis High performance liquid chromatography(HPLC)is the more versatile and economically viable quality assurance technique for soluble resin materials(References 4.4.4(a)-4.4.4(g)).HPLC involves the liq- uid-phase separation and monitoring of separated resin components.Dilute solutions of resin samples are prepared and injected into a liquid mobile phase which is pumped through column(s)packed with a stationary phase to facilitate separation and then into a detector.The detector monitors concentrations of the separated components,and its signal response,recorded as a function of time after injection,pro- vides a"fingerprint"of the sample's chemical composition.Quantitative information may be obtained if the sample components are known and sufficiently well-resolved,and if standards for the components are available.Size exclusion chromatography(SEC),an HPLC technique,is particularly useful in determining the average molecular weights and molecular weight distributions of thermoplastic resins (Reference 4.4.4(g)).Recent advances have resulted in improved and automated HPLC instrumentation that is rela- tively low cost and simple to operate and maintain. A powerful,but technically more demanding,technique for directly analyzing polymers is pyrolysis GC/MS(gas chromatography/mass spectroscopy).In this case,the sample only needs to be rendered sufficiently small to fit onto the pyrolysis probe.Not only can the polymer type be identified by comparing the resulting spectrum with standards,but volatiles and additives can be identified rapidly and quantita- tively,and polymer branching and crosslink density can sometimes be measured. Other chromatographic and spectroscopic techniques have also been considered (References 4.4.3(a),4.4.4(h)-4.4.4(I)).Gas chromatography (GC),GC head-space analysis,and GC-mass spec- troscopy are useful for analyzing residual solvents and some of the more volatile resin components. Combined thermal analysis-GC-mass spectroscopy can be used to identify volatile reaction products during cure (References 4.4.4(m)and 4.4.4(n)). 4.4.5 Molecular weight and molecular weight distribution analysis Techniques for evaluating polymer molecular weight(MW),molecular weight distribution(MWD),and chain structure are listed in Table 4.4.5.Size-exclusion chromatography(SEC)is the most versatile and widely used method for analyzing polymer MW and MWD.Once the solubility characteristics of a poly- mer are known,a suitable solvent can be selected for dilute solution characterization.THF is most often the solvent of choice for SEC,however,toluene,chloroform,TCB,DMF(or DMP)and m-cresol are also used.If the polymer's Mark-Houwink constants,K and a,in the solvent are known,size-exclusion chro- matography (SEC)can be applied to determine the polymer's average MW and MWD (Reference 4.4.5(a)).If the constants are unknown or the polymer has a complex structure (e.g.,branched,a co- polymer,or mixture of polymers),SEC still may be used to estimate the MWD and other parameters relat- ing to the structure and composition of the polymer.Although SEC indicates the presence of soluble non- polymeric components,high performance liquid chromatography(HPLC)is the better technique for char- acterizing residual monomers,oligomers,and other soluble,low MW sample components. 4-6

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-6 spectra for interpretation. In addition, the FTIR attenuated total reflection (ATR) and diffuse reflectance techniques may be applied for quality assurance of thermoset composite materials to assess their state of cure; i.e., residual epoxide concentration. (See Section 5.5.3) Although not as popular as IR, laser Raman spectroscopy complements IR as an identification tech￾nique and is relatively simple to apply (Reference 4.4.3(a)). As long as the specimen is stable to the high intensity incident light and does not contain species that fluoresce, little or no sample preparation is nec￾essary. Solid specimens need only be cut to fit into the sample holder. Transmission spectra are obtained directly with transparent specimens. For translucent specimens, a hole may be drilled into the specimen for passage of the incident light and a transmission spectra obtained by analyzing light scattered perpen￾dicular to the incident beam. The spectrum of a turbid or highly scattering specimen is obtained by ana￾lyzing the light reflected from its front surface. Powdered samples are simply tamped into a transparent glass tube and fibers can be oriented in the path of the incident beam for direct analysis. 4.4.4 Chromatographic analysis High performance liquid chromatography (HPLC) is the more versatile and economically viable quality assurance technique for soluble resin materials (References 4.4.4(a) - 4.4.4(g)). HPLC involves the liq￾uid-phase separation and monitoring of separated resin components. Dilute solutions of resin samples are prepared and injected into a liquid mobile phase which is pumped through column(s) packed with a stationary phase to facilitate separation and then into a detector. The detector monitors concentrations of the separated components, and its signal response, recorded as a function of time after injection, pro￾vides a "fingerprint" of the sample's chemical composition. Quantitative information may be obtained if the sample components are known and sufficiently well-resolved, and if standards for the components are available. Size exclusion chromatography (SEC), an HPLC technique, is particularly useful in determining the average molecular weights and molecular weight distributions of thermoplastic resins (Reference 4.4.4(g)). Recent advances have resulted in improved and automated HPLC instrumentation that is rela￾tively low cost and simple to operate and maintain. A powerful, but technically more demanding, technique for directly analyzing polymers is pyrolysis GC/MS (gas chromatography/mass spectroscopy). In this case, the sample only needs to be rendered sufficiently small to fit onto the pyrolysis probe. Not only can the polymer type be identified by comparing the resulting spectrum with standards, but volatiles and additives can be identified rapidly and quantita￾tively, and polymer branching and crosslink density can sometimes be measured. Other chromatographic and spectroscopic techniques have also been considered (References 4.4.3(a), 4.4.4(h) - 4.4.4(l)). Gas chromatography (GC), GC head-space analysis, and GC-mass spec￾troscopy are useful for analyzing residual solvents and some of the more volatile resin components. Combined thermal analysis - GC-mass spectroscopy can be used to identify volatile reaction products during cure (References 4.4.4(m) and 4.4.4(n)). 4.4.5 Molecular weight and molecular weight distribution analysis Techniques for evaluating polymer molecular weight (MW), molecular weight distribution (MWD), and chain structure are listed in Table 4.4.5. Size-exclusion chromatography (SEC) is the most versatile and widely used method for analyzing polymer MW and MWD. Once the solubility characteristics of a poly￾mer are known, a suitable solvent can be selected for dilute solution characterization. THF is most often the solvent of choice for SEC, however, toluene, chloroform, TCB, DMF (or DMP) and m-cresol are also used. If the polymer's Mark-Houwink constants, K and a, in the solvent are known, size-exclusion chro￾matography (SEC) can be applied to determine the polymer's average MW and MWD (Reference 4.4.5(a)). If the constants are unknown or the polymer has a complex structure (e.g., branched, a co￾polymer, or mixture of polymers), SEC still may be used to estimate the MWD and other parameters relat￾ing to the structure and composition of the polymer. Although SEC indicates the presence of soluble non￾polymeric components, high performance liquid chromatography (HPLC) is the better technique for char￾acterizing residual monomers, oligomers, and other soluble, low MW sample components

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization Light scattering,osmometry,and viscometry are also used to analyze polymer MW.Although seldom applied to synthetic polymers,sedimentation is an excellent technique for characterizing the MW of poly- mers having very large MW.The "special"techniques tend to be somewhat empirical or have limited util- ity and therefore are used less often. New techniques which show great promise for characterizing polymer chain structure also are listed in Table 4.4.5.One of the most promising new techniques is dynamic laser light scattering.Unlike SEC. dynamic light scattering can be applied to any soluble polymer,regardless of temperature or solvent,and does not require polymer standards for calibration.Figure 4.4.5 illustrates the MWD of poly (1,4-phenylenetereph-thalamide)(i.e.,KevlarTM)measured by the laser light scattering (Reference 4.4.5(b). 0 g , g 0 盖 0 ⊙ 7 8 0 8 g 0 10 10 MW FIGURE 4.4.5 Molecular weight distribution(MWD)of KevlarTM in concentrated sulfuric acid,using dynamic laser light scattering. As indicated,the polymer's MWD can be fully characterized using very little sample and a single solu- tion with concentrated sulfuric acid as the solvent. Dilute solution viscometry is a simple technique for determining the limiting viscosity number or intrin- sic viscosity [n]of soluble polymers (Reference 4.4.5(a)).The apparatus is inexpensive and simple to assemble and operate.The [n]of a polymer depends upon its hydrodynamic volume in the solvent and is related to the MW of the polymer. 4.4.6 General scheme for resin material characterization The following questions deserve careful consideration when developing procedures for preparing and characterizing polymer and polymer precursor(thermosetting resins and resin formulations)samples- What are the inherent characteristics of the polymer or prepolymer? Will certain operations cause irreversible changes in the sample? 4-7

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-7 Light scattering, osmometry, and viscometry are also used to analyze polymer MW. Although seldom applied to synthetic polymers, sedimentation is an excellent technique for characterizing the MW of poly￾mers having very large MW. The "special" techniques tend to be somewhat empirical or have limited util￾ity and therefore are used less often. New techniques which show great promise for characterizing polymer chain structure also are listed in Table 4.4.5. One of the most promising new techniques is dynamic laser light scattering. Unlike SEC, dynamic light scattering can be applied to any soluble polymer, regardless of temperature or solvent, and does not require polymer standards for calibration. Figure 4.4.5 illustrates the MWD of poly (1,4-phenylenetereph-thalamide) (i.e., Kevlar™) measured by the laser light scattering (Reference 4.4.5(b)). FIGURE 4.4.5 Molecular weight distribution (MWD) of KevlarTM in concentrated sulfuric acid, using dynamic laser light scattering. As indicated, the polymer's MWD can be fully characterized using very little sample and a single solu￾tion with concentrated sulfuric acid as the solvent. Dilute solution viscometry is a simple technique for determining the limiting viscosity number or intrin￾sic viscosity [η] of soluble polymers (Reference 4.4.5(a)). The apparatus is inexpensive and simple to assemble and operate. The [η] of a polymer depends upon its hydrodynamic volume in the solvent and is related to the MW of the polymer. 4.4.6 General scheme for resin material characterization The following questions deserve careful consideration when developing procedures for preparing and characterizing polymer and polymer precursor (thermosetting resins and resin formulations) samples - What are the inherent characteristics of the polymer or prepolymer? Will certain operations cause irreversible changes in the sample?

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization TABLE 4.4.5 Polymer molecular weights,molecular Standard Techniques Parameters Measured Size-Exclusion Chromatography Mol.wgt.averages and MWD,also provides (SEC)informa- tion relating to polymer chain branching,copolymer compo- sition,and polymer shape. Light Scattering(Rayleigh) Weight-average mol.wgt.Mw (g/mol),virial coefficient A2 (mol.cc/g),radius of gyration <R(A),polymer structure, anisotropy,polydispersity. Membrane Osmometry Number-average mol.wgt.M(g/mol),virial coefficient A2 (mol cc/g).Good for polymers with MW's in the range 5000 MW 105,lower MW species must be removed. Vapor Phase Osmometry Same as membrane osmometry except that the technique is best suited for polymers with MW<20,000 g/mol. Viscometry(dilute solution) Viscosity-average mol.wgt.Mn(g/mol)as determined by intrinsic viscosity [n](ml/g)relationship []KM,where K and a are constants. Ultracentrifugation or Sedimentation Sedimentation-diffusion average mol.wgt.Msd as defined by the relationship Md=S /D..Number-and z-average mol. wgt.,Mn and Mz.MWD determined by the relation S=kM2 where k and a are constants.Also provides information on the size and shape of polymer molecules. Special Techniques Parameters Measured Ebulliometry Number-average mol.wgt.M (g/mol)for M<20,000 g/mol. Cryoscopy Number-average mol.wgt.M(g/mol)for M<20,000 g/mol. End Group Analysis Number-average mol.wgt.M(g/mol generally for M< 10,000.Upper limit depends on the sensitivity of the ana- lytical method used. Turbidimetry Weight-average mol.wgt.M(g/mol)and MWD based upon solubility considerations and fractional precipitation of polymers in very dilute solutions 4-8

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-8 TABLE 4.4.5 Polymer molecular weights, molecular Standard Techniques Parameters Measured Size-Exclusion Chromatography Mol. wgt. averages and MWD, also provides (SEC) informa￾tion relating to polymer chain branching, copolymer compo￾sition, and polymer shape. Light Scattering (Rayleigh) Weight-average mol. wgt. Mw (g/mol), virial coefficient A2 (mol. cc/g2 ), radius of gyration z(A), polymer structure, anisotropy, polydispersity. Membrane Osmometry Number-average mol. wgt. Mn (g/mol), virial coefficient A2 (mol cc/g2 ). Good for polymers with MW's in the range 5000 < MW < 106 , lower MW species must be removed. Vapor Phase Osmometry Same as membrane osmometry except that the technique is best suited for polymers with MW < 20,000 g/mol. Viscometry (dilute solution) Viscosity-average mol. wgt. Mη (g/mol) as determined by intrinsic viscosity [η] (ml/g) relationship [η] = KMv where K and a are constants. Ultracentrifugation or Sedimentation Sedimentation-diffusion average mol. wgt. Msd as defined by the relationship Msd = Sw/Dw. Number- and z-average mol. wgt., Mn and Mz. MWD determined by the relation S = kMa where k and a are constants. Also provides information on the size and shape of polymer molecules. Special Techniques Parameters Measured Ebulliometry Number-average mol. wgt. Mn (g/mol) for Mn < 20,000 g/mol. Cryoscopy Number-average mol. wgt. Mn (g/mol) for Mn < 20,000 g/mol. End Group Analysis Number-average mol. wgt. Mn (g/mol generally for Mn < 10,000. Upper limit depends on the sensitivity of the ana￾lytical method used. Turbidimetry Weight-average mol. wgt. Mw (g/mol) and MWD based upon solubility considerations and fractional precipitation of polymers in very dilute solutions

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization weight distribution and chain structure. Principle Liquid chromatography technique.Separates molecules according to their size in so- lution and employs various detectors to monitor concentrations and identify sample components.Requires calibration with standard polymers. Measurement of scattered light intensities from dilute polymer solutions dependent upon solute concentration and scattering angle.Requires solubility,isolation,and in some cases fractionation of polymer molecules. Measurement of pressure differential between dilute polymer solution and solvent separated by a semi-permeable membrane.Colligative property method based upon thermodynamic chemical potential for polymer mixing. Involves isothermal transfer of solvent from a saturated vapor phase to a polymer so- lution and measurement of energy required to maintain thermal equilibrium.A colliga- tive property. Employs capillary or rotational viscometer to measure increase in viscosity of solvent caused by the presence of polymer molecules.Not an absolute method,requires standards. Strong centrifugal field is employed with optical detection to measure sedimentation velocity and diffusion equilibrium coefficients Sw and Dw.Sedimentation transport measurements of dilute polymer solutions corrected for pressure and diffusion pro- vides the sedimentation coefficient S.Permits analysis of gel containing solutions. Principle Measures boiling point elevation by polymer in dilute solution.A colligative property. Measures freezing point depression by polymer in dilute solution.A colligative prop- erty. The number or concentration of polymer chain end groups per weight or concentration of polymer are determined by specific chemical or instrumental techniques. Optical techniques are applied to measure the extent of precipitation as polymer solu- tion is titrated with a non-solvent under isothermal conditions or as the solution pre- pared with a poor solvent is slowly cooled. 4-9

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-9 weight distribution and chain structure. Principle Liquid chromatography technique. Separates molecules according to their size in so￾lution and employs various detectors to monitor concentrations and identify sample components. Requires calibration with standard polymers. Measurement of scattered light intensities from dilute polymer solutions dependent upon solute concentration and scattering angle. Requires solubility, isolation, and in some cases fractionation of polymer molecules. Measurement of pressure differential between dilute polymer solution and solvent separated by a semi-permeable membrane. Colligative property method based upon thermodynamic chemical potential for polymer mixing. Involves isothermal transfer of solvent from a saturated vapor phase to a polymer so￾lution and measurement of energy required to maintain thermal equilibrium. A colliga￾tive property. Employs capillary or rotational viscometer to measure increase in viscosity of solvent caused by the presence of polymer molecules. Not an absolute method, requires standards. Strong centrifugal field is employed with optical detection to measure sedimentation velocity and diffusion equilibrium coefficients Sw and Dw. Sedimentation transport measurements of dilute polymer solutions corrected for pressure and diffusion pro￾vides the sedimentation coefficient S. Permits analysis of gel containing solutions. Principle Measures boiling point elevation by polymer in dilute solution. A colligative property. Measures freezing point depression by polymer in dilute solution. A colligative prop￾erty. The number or concentration of polymer chain end groups per weight or concentration of polymer are determined by specific chemical or instrumental techniques. Optical techniques are applied to measure the extent of precipitation as polymer solu￾tion is titrated with a non-solvent under isothermal conditions or as the solution pre￾pared with a poor solvent is slowly cooled

MIL-HDBK-17-1F Volume 1,Chapter 4 Matrix Characterization TABLE 4.4.5 Polymer molecular weights,molecular Special Techniques Parameters Measured Chromatographic Fractionation Molecular weight distribution.An absolute MW technique is needed to analyze fractions. Melt Rheometry Weight-average mol.wgt.M (g/mol)and weight-fraction differential molecular weight distribution semi-empirical method. Gel-Sol Analysis of Crosslinked Poly- Gel fraction,Crosslink density mers Swelling Equilibrium Network structure,crosslink density,number-average mol. wgt.of chains between crosslinks M.. Promising Techniques Parameters Measured Laser Light Scattering (quasi-elastic, Same as Rayleigh light scattering plus trans-diffusion coeffi- line-broadening or dynamic) cient,molecular weight distribution,and information relating to gel structure. Field Flow Fractionation(FFF) Mol.wgt.averages and MWD.Requires calibration. Non-Aqueous Reverse-Phase High Mol.wgt.averages and MWD.Requires calibration. Performance Liquid Chromatography HPLC and Thin-Layer Chromatogra- phy TLC Supercritical Fluid Chromatography Mol.wgt.averages and MWD.Requires calibration. (SFC) Neutron Scattering Small Angle Weight-average mol.wgt.Mw(g/mol),Virial coefficient A2 (SANS) (mol-cc/g )Radius of gyration <Rz(A) 4-10

MIL-HDBK-17-1F Volume 1, Chapter 4 Matrix Characterization 4-10 TABLE 4.4.5 Polymer molecular weights, molecular Special Techniques Parameters Measured Chromatographic Fractionation Molecular weight distribution. An absolute MW technique is needed to analyze fractions. Melt Rheometry Weight-average mol. wgt. Mw (g/mol) and weight-fraction differential molecular weight distribution semi-empirical method. Gel-Sol Analysis of Crosslinked Poly￾mers Gel fraction, Crosslink density Swelling Equilibrium Network structure, crosslink density, number- average mol. wgt. of chains between crosslinks Mc. Promising Techniques Parameters Measured Laser Light Scattering (quasi-elastic, line-broadening or dynamic) Same as Rayleigh light scattering plus trans-diffusion coeffi￾cient, molecular weight distribution, and information relating to gel structure. Field Flow Fractionation (FFF) Mol. wgt. averages and MWD. Requires calibration. Non-Aqueous Reverse-Phase High Performance Liquid Chromatography HPLC and Thin-Layer Chromatogra￾phy TLC Mol. wgt. averages and MWD. Requires calibration. Supercritical Fluid Chromatography (SFC) Mol. wgt. averages and MWD. Requires calibration. Neutron Scattering Small Angle (SANS) Weight-average mol. wgt. Mw (g/mol), Virial coefficient A2 (mol-cc/g2 ), Radius of gyration z (A)