《纺织复合材料》课程参考文献（High Performance Thermoplastic Resins and Their Composites）02. Neat Thermoplastic Resins Properties.pdf_大学文库

2.Neat Thermoplastic Resins Properties 2.1 Introduction Plastics are commonly classified into two classes.thermoplastics or thermosets, depending on their behavior when heated (4.5.6).A thermoset polymer undergoes various degrees of cross-linking when cured by heat (or other means)[6l.The cross-linking reactions lead to the formation of an insoluble or infusible rigid product,a"set"product,in which chains are joined together to form a three-dimensional structure (5,7].In contrast,thermoplastic polymers do not undergo chemical changes during consolidation:changes are substantially physical [5,6].Generally.thermoplastics are melt fusible and can be consolidated by the application of heat and pressure only.They can be repeatedly sottened by heating and hardened by cooling.There are however some polymers categorized as thermosetting ther- moplastics or pscudo-thermoplastics [1.6,8].They are considercd as thermoplastic as they possess true thermoplastic properties but they are produced essentially like thermosets:they undergo some reaction chemistry during processing cycles.These materials require both curing and heat treatment for effective consolidation (6]. Thermoplastic polymers are not new:they have been known for a long time.It is only recently that the newer so-called high temperature or high performance thermoplastics have been introduced.The early thermoplastic polymers had predominantly aliphatic carbon back- bones in which flexible carbon chains could be extended and rotated into many configurations with relative ease [4,9.10].Rigidity was obtained by restricting the movement of the backbone chain elther by crystallinity such as in polyethylene and polypropylene or by the introduction of side groups as in polystyrene or polymethylmethacrylate.The major limitations with these early thermoplastics which are still on the market are their low elastic modulus,low glass transition temperature (Tg)and poor solvent resistance.In the past few years,a range of thermoplastics based on aromatic polymers have been developed which surmount these limitations.The introduction of rigid aromatic rings instead of aliphatic chains increases the intermolecular forces,thus restricting the movement of the backbone chain [4,10].Hence, mechanical properties,high temperature capability and solvent resistance are greatly improved and can be often equivalent or even better than the best thermosets.For ease of processing.groups such as ether.carbonyl,thioether.amide,methylene,ester.isopropylidine and sulfone are incorporated between the aromatic rings to render the polymer chain more flexible [1,10]. This section presents data on a number of these high performance thermoplastic resins which have the potential to be used as matrix material in fibre reinforced composites aimed at aircraft structural applications.The chemical structure,trade name and producers of these resins as well as their thermal and mechanical properties and solvent resistance are presented. A brief description of each polymer follows which highlights their important characteristics. 3

2. Neat Thermoplastic Resins Properties 2.1 Introduction Plastics are commonly classified into two classes, thermoplastics or thermosets, depending on their behavior when heated 14, 5, S]. A thermoset polymer undergoes various degrees of cross-linking when cured by heat (or other means] IS]. The cross-linking reactions lead to the formation of an insoluble or infusible rigid product, a “set” product, in which chains are joined together to form a three-dimensional structure 15, 71. In contrast, thermoplastic polymers do not undergo chemical changes during consolidation: changes are substantially physical 15, 61. Generally, thermoplastics are melt fusible and can be consolidated by the application of heat and pressure only. They can be repeatedly softened by heating and hardened by cooling. There are however some polymers categorized as thermosetting thermoplastics or pseudo-thermoplastics [ 1, 6. 81. They are considered as thermoplastic as they possess true thermoplastic properties but they are produced essentially like thermosets: they undergo some reaction chemistry during processing cycles. These materials require both curing and heat treatment for effective consolidation 161. Thermoplastic polymers are not new: they have been known for a long time. It is only recently that the newer so-called high temperature or high performance thermoplastics have been introduced. The early thermoplastic polymers had predominantly aliphatic carbon backbones in which flexible carbon chains could be extended and rotated into many configurations with relative ease [4. 9. 101. Rigidity was obtained by restricting the movement of the backbone chain either by crystallinity such as in polyethylene and polypropylene or by the introduction of side groups as in polystyrene or polymethylmethacrylate. The major limitations with these early thermoplastics which are still on the market are their low elastic modulus, low glass transition temperature (Tg) and poor solvent resistance. In the past few years, a range of thermoplastics based on aromatic polymers have been developed which surmount these limitations. The introduction of rigid aromatic rings instead of aliphatic chains increases the intermolecular forces, thus restricting the movement of the backbone chain [4, lo]. Hence, mechanical properties, high temperature capability and solvent resistance are greatly improved and can be often equivalent or even better than the best thermosets. For ease of processing, groups such as ether, carbonyl, thioether. amide, methylene. ester, isopropylidine and sulfone are incorporated between the aromatic rings to render the polymer chain more flexible 11. 101. This section presents data on a number of these high performance thermoplastic resins which have the potential to be used as matrix material in fibre reinforced composites aimed at aircraft structural applications. The chemical structure, trade name and producers of these resins as well as their thermal and mechanical properties and solvent resistance are presented. A brief description of each polymer follows which highlights their important characteristics. 3

4 High Performance Thermoplastic Resins and Their Composites 2.2 Properties of Neat Thermoplastic Resins 2.2.1 Chemical Structure and Some Physical Properties Table 1 lists the high performance thermoplastic polymers that are discussed in the present report.Although this list is not exhaustive,it provides a good indication of the thermoplastics that have been and are being investigated for use as matrix materials for high performance composites.Most of these neat resins are either commercially available or nearly so,in either industrial or developmental quantities.Some of them are provided as a neat resin or filled with short fibres but not yet reinforced with continuous fibres in a prepreg tape or fabric form.Although it is included in the present list,polyphenylquinoxaline (PPQ)is not expected to be avallable in the form of fibre reinforced matrix because of its low modulus,high viscosity and its high cost. Table 2 presents the chemical structure of some of these thermoplastics.The dominant aromattc character in their polymer backhone is clearly shown.Density.Poisson's ratio. Limiting Oxygen Index(L.O.I.)and viscosity are presented in Table 3.Density varles from 1.15 to 1.45 depending on the thermoplastic matrix:the polyamide J-2,a product from E.I.Dupont de Nemours,has the lowest density while N-polymer,a polyimide from Dupont and Eymyd,a polyimide from Ethyl Corporation.have the highest. The melt viscosities of high-molecular weight thermoplastics are much higher than most thermoscts.At processing temperature,thermosets have viscosities less than 1000 poise [2],which is much less than the viscosities presented in Table 3 for thermoplastics.The low viscosity of epoxy formulations results in high melt nlow properties in the uncured state leading to good wetting of the fibres during prepreg manufacture [1l.Figure 1 shows the relationship between solution viscosity.melt viscosity,number average molecular weight and the glass transition temperature (Tg)presented in [9].As shown,the desired high Tg leads inevitably to high melt viscosity.Unfortunately,the high melt viscosity of thermoplastics renders processing difficult as high processing temperatures are required to achieve a low melt viscosity for good consolidation and fibre impregnation:and the viscosity may still be too high for complete impregnation of continuous fibre bundles.Processing becomes difficult at melt viscosities above 5500 poise [9].Melt viscosities of 102 to 104 poise are desirable for the fabrication of composites [1].It is then a question of compromise between processability of thermoplastic composites and their high temperature performance as reflected by Tg. L.O.I.numbers found in Table 3 give an indication of the material's resistance to burning,which may be very important in certain applications.For example,aircraft interiors such as sidewall panels,storage bins.partitions,galley doors and celling panels have to meet certain combustibility requirements to comply to the more and more stringent U.S.Federal Aviation Administration (FAA)cabin safety regulations [57]."L.O.I.is the minimum

4 High Performance Thermoplastic Resins and Their Composites 2.2 Properties of Neat Thermoplastic Resins 2.2.1 Chemical Structure and Some Physical Properties Table 1 lists the high performance thermoplastic polymers that are discussed in the present report. Although this list is not exhaustive, it provides a good Indication of the thermoplastics that have been and are being investigated for use as matrix materials for high performance composites. Most of these neat resins are either commercially available or nearly so, in either industrial or developmental quantities. Some of them are provided as a neat resin or filled with short fibres but not yet reinforced with continuous fibres in a prepreg tape or fabric form. Although it is included in the present list, polyphenylquinoxaline (PPQ) is not expected to be available in the form of fibre reinforced matrix because of its low modulus, high viscosity and its high cost. Table 2 presents the chemical structure of some of these thermoplastics. The dominant aromatic character in their polymer backbone is clearly shown. Density, Poisson’s ratio, Limiting Oxygen Index (L.O.I.) and viscosity are presented in Table 3. Density varies from 1.15 to 1.45 depending on the thermoplastic matrix: the polyamide J-2, a product from E.I. DuPont de Nemours, has the lowest density while N-polymer, a polyimide from DuPont and Eymyd, a polyimide from Ethyl Corporation, have the highest. The melt viscosities of high-molecular weight thermoplaslics are much higher than most thermosets. At processing temperature. thermosets have viscosities less than 1000 poise [2]. which is much less than the viscosities presented in Table 3 for thermoplastics. The low viscosity of epoxy formulations results in high melt flow properties in the uncured state leading to good wetting of the fibres during prepreg manufacture 111. Figure 1 shows the relationship between solution viscosity, melt viscosity, number average molecular weight and the glass transition temperature (Tg) presented in 191. As shown, the desired high Tg leads inevitably to high melt viscosity. Unfortunately, the high melt viscosity of thermoplastics renders processing difficult as high processing temperatures are required to achieve a low melt viscosity for good consolidation and fibre impregnation: and the viscosity may still be too high for complete impregnation of continuous fibre bundles. Processing becomes difficult at melt viscosities above 5500 poise [9]. Melt viscosities of 102 to 104 poise are desirable for the fabrication of composites [ 11. It is then a question of compromise between processability of thermoplastic composites and their high temperature performance as reflected by Tg. L.O.I. numbers found in Table 3 give an indication of the material’s resistance to burning, which may be very important in certain applications. For example, aircraft interiors such as sidewall panels, storage bins, partitions. galley doors and ceiling panels have to meet certain combustibility requirements to comply to the more and more stringent U.S. Federal Aviation Administration (FAA) cabin safety regulations [57]. “L.O.I. is the minimum