《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