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. 4-4MIL-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