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Spectroscopic analysis of compatibilized polymer blends
CHAPTER 13
Spectroscopic analysis of compatibilized polymer blends Ajay Vasudeo Rane, Sabana Ara Begum, Krishnan Kanny Composite Research Group, Department of Mechanical Engineering, Durban University of Technology, Durban, KwaZulu-Natal, South Africa
Abbreviations FTIR IR NMR PA6 PP LDPE PVC EVAL PMMA TPO DMAP SAAS PvPh PvAc MAH PVIm THF PLA
Fourier-transform infrared spectroscopy Infrared Nuclear Magnetic Resonance Polyamide 6 Polypropylene Low-density polyethylene Polyvinyl chloride Poly(ethylene-co-vinyl alcohol) Polymethyl methacrylate Thermoplastic polyolefin 4-dimethylaminopyridine Styrene-acrylic acid Poly(vinyl phenol) Poly(vinyl acetate) Maleic anhydride Poly (N-vinylimidazole) Tetrahydrofuran Polylactic acid
13.1 Introduction The internal structure of a material, simply called the structure, can be studied at various levels of observation. The degree of magnification required to study them by various methods is a measure of the level of observation. The details that are revealed or disclosed at a certain level of magnification are generally different from the details disclosed at some other level of magnification [1]. Depending on the level, the structure of materials can be classified as [1]: a. Macrostructure b. Microstructure Compatibilization of Polymer Blends ISBN 978-0-12-816006-0 https://doi.org/10.1016/B978-0-12-816006-0.00013-X
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Substructure Crystal structure Electronic structure Nuclear structure Macrostructure is the structure of a material as seen by the naked eye or low power magnification. It deals with the size, shape, and atomic arrangements in a crystalline material. The individual crystal in a polycrystalline material such as cast brass door knob is visible when polished and etched by constant contact with human hand and sweat. Similarly, large thin zinc crystal can sometimes be seen on the surface of heavily galvanized objects and they are called macroscopic. A macrostructure looks very similar to a sand grain and has more or less the same dimension [1]. Macrostructures may be studied either directly on the surface of the work (a casting, for example) or on a fracture or more frequently on specimens or samples cut out of large billets (ingots, forging, etc) or articles. And there are standard procedures available for macroexamination to reveal flaws and segregation in a material. Microstructure generally refers to the structure as observed under a microscope at magnification from 75 to 1500. A microstructure looks very similar to a dust particle. Microscopic examination reveals greater detail of the structure of a material but in almost every instance some sort of special specimen preparation and mounting is necessary [1]. Optical microscopes are employed to investigate the structure of materials and they enable only those details of the structure to be observed that are larger than 0.15 to 0.2 microns. Macrostructure and microstructure are two words relating to the same general type of phenomena and differ only in the degree of magnification required to study them. Substructure refers to structure obtained by using a microscope with a much higher magnification than optical microscope. And as such a wealth of new information on crystal imperfections such as dislocation and on very small particles of a few hundred angstroms in size is obtained and studied. At present, the electron microscope is used to study the substructure of the material and an effective magnification of 100,000 may be obtained [1]. Details of the object may be distinguished which are from 30 to 50A⁰ in size. The field ion microscope is a technique which produces images of individual atom. Crystal structure tells us the details of the atomic arrangement within a crystal, and it resembles a molecule. Electronic structure of a solid usually concerns the electrons in outer most shells of individual atoms that form the solid. Spectroscopic studies are very useful in determining the electronic c. d. e. f.
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structure. Nuclear structure is studied by nuclear spectroscopic techniques such as nuclear magnetic resonance and Mössbauer studies [1]. Analytical technique is one of the most powerful tools available for the study of atomic and molecular structure and is used in the analysis of most of the samples. Analytical technique or spectroscopy deals with the study of interaction of electromagnetic radiation with matter. During the interaction, the energy is absorbed or emitted by the matter. The measurements of this radiation frequency (absorbed or emitted) are made using spectroscopy [2]. The study of spectroscopy can be carried out under the following titles: Atomic spectroscopy and molecular spectroscopy. Atomic spectroscopy deals with interaction of electromagnetic radiation with atomsdatoms absorb radiation and get excited from ground state electronic energy level to another- and molecular spectroscopy deals with interaction of electromagnetic radiation with molecules, which results in transition between rotational, vibrational, and electronic energy levels. Likewise there are two spectrumsdabsorption spectrum and emission spectrum; when a molecule absorbs photon of energy and undergoes a transition from lower energy level to the higher energy level, the measurement of this decrease in intensity of radiation is the basis of absorption spectroscopy, the spectrum thus obtained is called absorption spectrum. If the molecule comes down from excited state to the ground state with the emission of photons of energy, the spectrum obtained is called emission spectrum [2]. Various spectroscopic techniques like infrared spectroscopy, nuclear magnetic resonance spectroscopy, electronic spectroscopy, mass spectroscopy, and conjoint spectroscopy have completely altered the face of organic chemistry. Most researchers will use infrared spectroscopy first, and nuclear magnetic resonance spectroscopy will follow; electronic spectroscopy is more limited in scope and mass spectroscopy in general the most expensive [3]. Spectroscopy should provide high-resolution, narrow line width spectra enhancing selectivity and structural information in case of polymers. Polymers and their systems (blends and composites) form multifaceted mixtures of structure and molecules, for which spectroscopic probe should selectively determine different structures at a point in time. It should have the ability to sense and detect very low levels of structure in the complex polymer systems, as minor structural changes effect physical and mechanical properties of polymeric systems. The spectroscopic probe should be specific in providing content information, in line with structure, form, and order of network in complex polymer system. The technique used for measurement must be nondestructive and noninvasive, so that polymer specimens can be
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evaluated by other characterization methods in addition to spectroscopic analysis. Polymer specimens are available in any useful (adhesive, film, coating, fiber, and film) form, and the probe should be able to study them. Majority of the spectroscopic analysis techniques do not satisfy the specifications of the spectroscopic probe for polymers. However, four spectroscopic techniques, Fourier transform infrared (FTIR), Raman, highresolution NMR spectroscopy of the solid state, and mass spectroscopy, fit into the criteria and these techniques are used individually or in combination, providing detailed structural information on polymers for purposes required, i.e., quality control or research and development [4]. Infrared spectroscopy is one of the most often and successfully implemented techniques used as spectroscopic tools for the study of polymers, i.e., structural determination. Infrared spectroscopy is a quick and thin-skinned method with easy sampling techniques, inexpensive instrumentation setup, easy and simple operation, in line with inexpensive service and maintenance. Interpretation of spectra is not complex, with ease in learning, although better discussion and interpretation is done by professionals. Although infrared spectroscopy is specific about the amount of certain structures in complex polymeric systems, quantitative measurements are still a challenge [4]. Raman spectroscopy and IR are complementary owing to differences in the selection rules which generate spectral information not available from IR. Most often, Raman spectroscopy is useful and advantageous when ease of sampling and remote sampling is required and in characterizing aqueous solutions. Apart from the abovementioned, Raman spectroscopy is used more as a research tool than an analytical tool for complex polymer systems due to ubiquitous fluorescence which occurs with polymer samples. Yet, remarkable improvement has been made recently due to which Raman spectroscopy is being used as tool for polymer characterizations [4]. Polymer blends are used for a range of applications with a motive to enhance the specific properties of individual homopolymers in the complex mixture. However, this complex mixture should be stable at molecular levels and become compatible. The stability of complex mixtures is dependent on individual properties of homopolymers in the polymer blend, degree of mixing, and physical and chemical interactions. Nearly all pairs of polymers are not miscible on a molecular level, resulting in phase separation, leading to decrement in mechanical properties. Determining glass transition temperature (Tg) confirms the presence of one polymer in the other polymer, i.e., coexisting phases, where shift of Tg takes place toward one of the polymer in complex polymeric systems. Single Tg is
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observed for amorphous polymer blends. Nature and reproducibility of interactions leading to compatibility, and changes involved with respect to time and temperature are important information in preparation of compatible blends. Even though thermoanalysis and NMR spectroscopy give information on the compatibility of blends, none of these techniques are favorable for quick examination of the kinetics of the phase separation process. On the other hand, FTIR spectroscopy is able to establish the nature and level of molecular interactions within polymer mixture and the change in these interactions with aging. Compatibility of a blend, in terms of IR, owes to the presence of a detectable ‘interaction’ spectrum that arises in comparison to the spectra of the two homopolymers involved in blending. In case of compatible polymers, an interaction spectrum with frequency shifts and intensity modifications that are fundamental to the system will be observed. For incompatible polymers, the spectrum is spectral sum, within experimental error, of the spectra of the two homopolymers involved in blending [4]. Interaction spectrum can be quantitatively determined by using factor analysis [5]. Observations in spectrum of polymer blends with varied volume fractions of individual polymer determine if interaction spectrum is a contributing factor. Further number of components in the blend spectra is evaluated by factor analysis. Three components are expected in case of compatible blends, and two for incompatible blends. Polymer blends [6] as a function of composition and temperature during solvent evaporation are studied and minimum indicator function values for both blends depict a three-component system, which means both blends are compatible. Double subtraction spectra of two homopolymers were used in determining the interaction parameter. Shift in frequencies and intensities in interaction spectrum indicate interaction between two homopolymers in polymer blend. Interaction spectra for polymer compositions, i.e., PVF2-PVAc heat treated at 75 and at 175 C are shown in Fig. 13.1A and B, respectively. Hydrogen bonds between the two components are the most IR observable molecular interactions [7]. Fig. 13.2 shows the IR spectra at room temperature for THF-casted poly(vinyl phenol) (PVPh)-PVAc blends containing varied quantity of PVAc in the regions from 3800 to 3000 cm1 and from 1800 to 1650 cm1 [8]. Carbonyl and hydrogen bonding IR regions have large spectral differences. Hydrogen bonding between polymeric chains results in frequency shifts and changes in band intensities indicating molecular interactions.
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Figure 13.1 (A) Interaction spectra of poly(vinylidene fluoride)-poly(vinyl acetate) (PVF2-PVAc) blends obtained immediately after heat treatment at 75 C for 1 h. Spectra were collected for blends having weight percent ratios of 10:90 to 90:10 PVF2-PVAc. (B) Interaction spectra of PVF2-PVAc blends heat treated at 175 C.
Figure 13.2 The IR spectra in the regions of 3800 and 1800 1650 cm1 recorded at room temperature of poly(4-vinylphenol)-poly(vinyl acetate) (PVAc) (PVPh-PVAc) blends cast from tetrahydrofuran containing 100 (a), 80 (b), 50 (c), 20 (d), and 0 (e) wt% PVAc.
Adding a small amount of comonomer into polymer mixtures that do not possess hydrogen bonding between each other, leads to compatibility, and acts as chemical links between the two homopolymers is an interesting method [9]. Fig. 13.3 shows the interaction spectrum (after double
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Figure 13.3 The IR spectra of styreneeacrylic acidepoly (methyl methacrylate) (SAASPMMA) (4:1) blend (A), pure SAAS (B), pure PMMA (C), and the interaction spectrum (AeBeC).
subtraction) for styrene (92%)eacrylic acid copolymer, the 89% styrenee acrylic acid (SAAS)epoly (methyl methacrylate) (PMMA) blend (4: 1), where hydrogen bonding has been introduced in the blends to make them compatible. Intermolecular interactions in NMR can be determined using crosspolarization, where carbons that are dipolar-coupled to protons provide 13 C resonances, whereas deuterated carbons will not provide any type of NMR signal except they are in close contact with protons on neighboring molecules. Cross-polarization is used to probe polymer mixtures and to study spatial order for mixtures of protonated and deuterated polymer blends [10]. Degree of mixing for processing aid is studied with deuterium approach [11]. Detailed information on protonated and deuterated carbons can be read in cited references [4]. Solid-state NMR is widely used to determine the miscibility in multicomponent polymer blends [12,13]. Conventionally, miscibility of polymers is characterized by locating glass transition temperature in a differential scanning calorimetry, wherein a single glass transition means miscible blend [14,15]. In NMR, identification via determining perturbation of the isotropic chemical shiftsetype of interactions, and if the specific interactions are due to hydrogen bonding, molecular complexes or chargeetransfer interactions can be identified. Triple 1H/13C/14N resonance experiment was used to evidence the presence of template complex formation in blends of poly-(methacrylic acid) (PMAA) and poly (N-vinylimidazole) (PVIm) [16]. Loss in spin echo
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intensity indicates a specific interaction between the carbonyl group of PMAA and the imidazole ring of PVIm, confirming formation of the polymer template complex in the polymer blend. NMR determines homogeneity in blends from molecular level to a few hundred A, wherein phase information is obtained on three different scalesdchanges in chemical shifts are monitored to get information on a molecular level. Blend possessing two different HT1s and two different HT1r indicates a single domain and sizes larger than about 500 A, one HT1r but H two T1s represent domain sizes ranging between 50 and 500 A. Only one H H T1r and one T1s indicate domain sizes smaller than about 50 A [16]. If proton relaxation times of the pure components show no significant differences, NMR method is limited to determine miscibility in polymer blends. Spin diffusion is also able to describe the heterogeneity in polymer blends [17]. Spin diffusion experiment classically consists of evolution stage generating initial polarization gradient between the components of the polymer blend; following a mixing stage, wherein time spin diffusion occurs and, finally, a detection stage for observing the follow-up 1H magnetization. Spin gradient can be generated based on mobility differences or on 1H chemical shift differences for polymer blends. Spin diffusion is governed by the dipolaredipolar interaction and for a dense rigid proton system. Spin diffusion rate is dependent on the space between nuclei as spin diffusion is restricted to molecules in vicinity. For occurrence of spin diffusion between two species they must be mixed closely on the molecular level. Useful semiquantitative information about domain size can be obtained [4] from the equation: ðr2 Þ ¼ 6Ds s where (r 2) is the mean square diffusive path length Ds is the spin-diffusion constant and is of order 4e7 1016 m2/s in the laboratory frame and half this magnitude in the rotating frame s is the time for a fundamental step in the random walk As HT1 is usually of the order of 7 101 s and HT1r of 102 s, the maximum diffusive path lengths range from 50 nm to about 2 nm, respectively. Single relaxation time will be observed if the two polymers in the blend are from two independent domains where the domain size is smaller than (r2), and two relaxation times when the domains are larger than (r2). Fig. 13.4B represents the carbonyl area spectrum of polymer blend along with the spectrum of maleic anhydride grafted polypropylene
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Figure 13.4 (A) Melt torque of low-density polyethylene/polypropylene 50/50 w/w blends: (a) without compatibilizer; (b) with 10 wt% compatibilizer (B) Fourier-transform infrared spectroscopy spectra of: (a) polypropylene-graft-maleic anhydride (PP-g-MA); (b) the product of reaction between PP-g-MA and poly(ethylene-co-vinyl alcohol).
copolymer. Characteristic peaks at 1863 and 1787 cm1 are ascribed to the five members saturated anhydride ring in grafted copolymer. While in spectra of polymer blends, they are attenuated and an occurrence of broad peak between 1750 and 1680 cm1 is noted. Maximum peak at 1727 cm1 is attributed to ester groups formed by the reaction shoulder at 1713 cm1 due to presence of carboxylic groups. Reaction between PP-g-MAH and EVAL (also took place in all PP/LDPE blends containing compatibilizer, as indicated in FTIR spectra). These results confirm that a reaction between maleic anhydride and hydroxyl groups definitely took place during blending, which increased while blending polymers as indicated in Fig. 13.4A. Adding compatibilizer improves mechanical properties of polymer blends. Tensile strength showed maximum value by adding 20 wt% compatibilizer, while impact strength enhancement was obtained by adding 10 wt% compatibilizer (see Fig. 13.5). Increased interfacial adhesion between the two polymers in their blends leads to better dispersion of the minor component into the matrix and increases the mechanical properties of polymer blends [18]. Raman spectra of PP and LDPE before blending were recorded as in Fig. 13.6A and B. Vibrations at 1105 and 810e860 cm1 are characteristic peaks of polypropylene and peaks at 1128 and 1062 cm1 are important peaks for polyethylene as illustrated in Fig. 13.6B. It was established that the spherical parts are PP and the continuous phase is LDPE, in view of the fact that their spectra are alike to those of the pure polymers (Fig. 13.6C). PP characteristic peaks were recorded at 1105 cm1 and at 810e860 cm1
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Figure 13.5 Low-density polyethylene/polypropylene blends for several compatibilizer contents: (a) 0 wt%, (b) 2.5 wt%, (c) 5 wt%, (d) 10 wt%, and (e) 20 wt%d(A) tensile strength, (B) elongation at break, and (C) impact strength.
(double peak, Fig. 13.6C-b) when probed at spherical domain. Additionally, peak at 2810e2950 cm1 when compared with the analogous peak of pure PP, it was confirmed that the spherical domains are polypropylene. Characteristic peaks of polyethylene at 1128 cm1 and at 1062 cm1 were present in flattened area surrounding spherical domains (Fig. 13.6C-a). Moreover, the double peak at 2820e2940 cm1 is similar as the analogous one in pure LDPE, which confirms the presence of polyethylene surrounding spherical domains of polypropylene and supports the intuitive rule from emulsions that in polymer blends the minor component forms the dispersed phase [18]. Characteristic peaks of both polymers exist in all areas in compatibilized blend (see Fig. 13.6D), as PP peaks dominate in continuous phase, whereas LDPE peaks are prominent in the small spherical domains (see Fig. 13.7). Characteristic peaks of LDPE at 1128 and 1062 cm1 appear with a very small intensity in spectra of spherical domains in uncompatibilized blend (Fig. 13.6E-c). As these peaks do not exist in the spectrum of pure PP, a conclusion that the two polymers show signs of a limited mutual solubility can be made. Intensity of two peaks increases, after
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Figure 13.6 Raman Spectra (A) pure polypropylene (PP) (B) pure low-density polyethylene (LDPE) (C) PP/LDPE 25/75 w/w blend focusing on: (a) spherical parts; (b) continuous phase (D) PP/LDPE 75/25 w/w blend focusing on: (a) continuous phase; (b) spherical domains (E) in the region 1200e950 cm1 of PP/LDPE blends: (a) pure PP; (b) pure LDPE; (c) spherical domains in PP/LDPE 25/75 w/w blend without compatibilizer; (d) spherical domains in PP/LDPE 25/75 w/w blend with 10 wt% compatibilizer (F) in the region 1200e750 cm1 of PP/LDPE blends: (a) pure PP; (b) pure LDPE; (c) flattened area in PP/LDPE 25/75 w/w blend with 10 wt% compatibilizer.
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Figure 13.7 Scanning electron image of fracture surface obtained from impact specimens (A) (a) 25/75 w/w, (b) 50/50 w/w, and (c) 75/25 w/w (B) polypropyleneelowdensity polyethylene (PPeLDPE) blends compatibilized with 10 wt% compatibilizer: (a) PP/LDPE, 25/75 w/w; (b) PP/LDPE, 50/50 w/w; (c) PP/LDPE, 75/25 w/w.
compatibilization (Fig. 13.6E-d) due to EVAL copolymer which is located at interface with maleic anhydride grafted polypropylene. Compatibilizer increases mutual solubility of the two polymers in polymer blend. Comparable annotations were made for the continuous phase. Characteristic absorption of polypropylene at 810e860 cm1 (weak, double peak) was made when flattened area around the PP domain was focused, as seen in Fig. 13.6F-c, which confirms the presence of polypropylene even in the flattened area surrounding the spherical domain [18].
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Micro-Raman spectroscopy seems to be an important tool for studying polymer blend morphology, as this has verified that PP and LDPE are immiscible with minor mutual solubility, allowing a clear detection of the dispersed phase in polymer blends [18]. Fig. 13.8 shows infrared spectra of: (a) PP (70)/PA6 (30) uncompatibilized blend showing a characteristic peak at 1640 cm1, for amide carbonyl group, and (b) represents compatibilized blend of the PP (60)/PA6 (30)/PP-g-MA (10) displaying three large peaks owing to the presence of imide linkages [19]. Imide group absorbances at 1779, 1726, and 1710 cm1 are recognized to in-phase, free, and hydrogen-bonded out-ofphase carbonyl vibrations, respectively; carbonyl stretch vibrations at 1774 and 1703 cm1 [15], and ring absorptions at 1775 and 1730 cm1 [20] are also noted by other group. In Gaussian deconvolution of the three large peaks in compatibilized blend (see inset in Fig. 13.8), the peak at 1764 cm1 represents carbonyl vibration of the imide group and 1710 cm1 to carbonyl vibration of the carboxylic acid from maleic anhydride grafted polypropylene unreacted. Predicted reaction is shown in Fig. 13.9. To make this predicted reaction clear, the PA6 domains were removed with formic acid. IR spectra of uncompatibilized blend without PA6 and compatibilized blend after PA6 extraction are shown in Fig. 13.10A and B, respectively. Fig. 13.10A shows only peaks assigned to
Figure 13.8 Infrared spectra of blends: (A) polypropylene (PP)/polyamide 6 (PA6) at 70/30 wt%; (B) PP/PA6/polypropylene-graft-maleic anhydride at 60/30/10 wt%. The insert shows a Gaussian deconvolution for the spectrum of the compatibilized blend in the range 1850 to 1600 cm1.
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Figure 13.9 Scheme of interface grafting by reaction between a carboxyl group of maleic anhydride and a polyamide amino end group.
Figure 13.10 Infrared spectra for the blend with polyamide 6 extraction: (A) uncompatibilized; (B) compatibilized.
PP molecules and confirms the nonexistence of interfacial interactions, while Fig. 13.10B exhibits absorbances at 1640 and 1730 cm1 due to carbonyl group and carbonyl imide linkage, in PA6 respectively. This discussion concludes the presence of the imide linkage at the interface of two polymeric components [21]. Table 13.1 gives the detail of peaks in PVC and PMMA in their pure form, as well as shifts in their peaks after blending. Fig. 13.11D is spectra of pure PVC, pure PMMA, and PVCePMMA blends. Peak at 1333 cm1 of pure PVC represents CH2 deformation, where relative intensity decreases PVC content decreases. Peak at 1254 cm1 is assigned to CH-rocking vibration. PVC when blended with PMMA forms small shoulder at the longer wavenumber. A doublet with increasing PMMA at 1271 and 1242 cm1 is observed. Relative intensity of the shoulder increases with increasing PMMA content. At 70% PMMA, the shoulder intensity is higher compared to that of the original band, confirming the complexation of PVCePMMA blends [22]. IR spectra of neat TPO and TPOeMAH are shown in Fig. 13.12A. Maleic anhydrideegrafted TPO shows new absorption peaks at 1864 cm1
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Table 13.1 Characteristics peaks in polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) and shifts in PVC/PMMA blends [22]. In PVC Shifts
2911 cm1 1333 cm1 1254 cm1 959 cm1 834 cm1 616 cm1
C H stretching CH2 deformation CH-rocking CH wagging CeCl stretching cis CH wagging
In PMMA 1
2951 cm 1721 cm1 1449 cm1 1159 cm1
1244 cm1 966 cm1 841 cm1 Shifts
CH stretching C O stretching CH3 stretching O CH3 stretching
1732 cm1 1435 cm1 1150 cm1
Figure 13.11 (A) Pure polyvinyl chloride (PVC) (B) pure polymethyl methacrylate (PMMA) (C) PVC: PMMA (30:70) blend (D) (a) pure PVC, (b) pure PMMA, (c) PVC: PMMA (70:30), (d) PVC: PMMA (50:50), and (e) PVC: PMMA (30:70) complexes.
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Figure 13.12 Fourier-transform infrared spectroscopy spectrum of (A) polylactic acid (PLA) and thermoplastic polyolefin (TPO)-derived copolymers (a) neat TPO; (b) maleic anhydrideemodified TPO; (c) TPOePLA copolymer; (d) neat PLA. (B) TPOePLA which was synthesized under various conditions (a) reaction temperature as variable; [TPO] 1 /4 10 wt%, [PLA] 1/4 20 wt%, [4’-Dimethylamino] 1/4 0.8 M. (b) 4-dimethylaminopyridine concentration as variable; [TPO] 1/4 10 wt%, [PLA] 1/4 20 wt%, reaction temp 1/4 140 C. (C) 1H nuclear magnetic resonance spectrum of TPOePLA copolymer. (D) Stressestrain curve of neat PLA and PLA/TPO blend.
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and 1786 cm1 related with the asymmetric and symmetric stretching of CO in the succinic anhydride units. Peak at 1786 cm1 corresponds to the maleic anhydride oligomeric segments in the functionalized polyolefin. Fig. 13.12A-c represents absorption peaks of PLAeTPO copolymer, with PLA carbonyl stretching at 1758 cm1; a set of characteristic absorptions in the fingerprint region of 1500e1000 cm1 were also present, like those of neat PLA displayed in Fig. 13.12A-d [23]. Infrared spectroscopy was used to determine the grafting ratio on PLA with respect to concentration of maleic anhydride and temperature of reaction. Peaks at 1786 cm1 and 1758 cm1 were observed and represented concentration of anhydride groups and PLA carbonyl stretching absorption in the TPOePLA copolymer, respectively. Decrease in absorption strength at 1786 cm1, broadening of carbonyl peak, and the appearance of absorption shoulder near 1758 cm1 as the reaction temperature increased were observed as shown in Fig. 13.12B-a, intensity of absorption at 1786 cm1 decreased as the DMAP concentration increased, but the PLA carbonyl absorption at 1758 cm1 intensified, indicating high reactivity of graft reaction at high temperature and DMAP concentration because more anhydride groups were consumed and more PLA chains were grafted. Esterification reaction of TPOeMAH with PLA, catalyzed by DMAP, was in line with a transesterification reaction, depolymerizing PLA. Mechanical properties of blends were higher than neat PLA [23].
13.2 Conclusion Infrared spectroscopy, qualitatively analyses starting materials, finished products, and the components in polymer blends. FTIR spectroscopy is reliable, fast, and cost-effective. In this chapter, analysis of IR spectra of typical polymer and polymer blends samples focused on identification of hydrogen bonding and miscibility in polymer blends. Solid-state NMR gives information on miscibility among polymers, with a precise ability to measure the length scales of mixing nearby by other experimental tools (i.e., traditional calorimetric methods), and to detect the inter- and intramolecular interactions responsible for miscibility in polymers. Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength than mid-IR spectroscopy which makes it possible to focus visible laser light to much smaller spot sizes (400 nm in air and 240 nm with an oil immersion objective) than may be characterized by mid-IR radiation.
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References [1] Hajra Choudhury SK, Hajra Choudhury AK. Materials science and process. Published by Indian Book Distributing Co.; 2009. ISBN 13: 9780906216002. [2] Ravikrishnan A. Engineering chemistry e I. Sri Krishna Publications; 2008. [3] Kemp W. Organic spectroscopy. 3rd ed. PALGRAVE Publishers; 2012. ISBN 978 1 4039 0684 7. [4] Koenig JL. Spectroscopy of polymers. New York: Elsevier; 1999. ISBN 0444100318. [5] Koenig JL, Tovar MJM. Appl Spectrosc 1981;35:543. [6] Sargent M, Koenig JL. Vib Spectrosc 1991;2:21. [7] Coleman MM, Painter EC. Appl Spectrosc Rev 1984;20:255. [8] Allara DL. Appl Spectrosc 1979;33:358. [9] Jo WH, Cruz CA, Paul DR. J Polym Sci B Polym Phys 1989;27:1057. [10] Schaefer J, Sefcik MD, Stejskal EO, McKay RA. Macromolecules 1981;14:188. [11] Hewitt JM, Henrichs EM, Scozzafava M, Scaringe RE, Linder M, Sorriero LJ. Macromolecules 1984;17:2566. [12] Belfiore LA, Lutz TJ, Cheng C. Solid state NMR detection of molecular level mixing phenomena in strongly interacting polymer blends and phase separated copolymers. New York, NY: Plenum; 1991. [13] Guo M. Trends Polym Sci 1996;4:238. [14] Colemen MM, Painter EC. Prog Polym Sci 1995;20:1. [15] Olabisi O, Robeson LM, Shaw MT. Polymer-polymer miscibility. New York, NY: Academic Press; 1979. [16] Ruhnau EC, Veeman WS. Macromolecules 1996;29:2916. [17] Campbell GC, VanderHart D. J Magn Reson 1992;96:69. [18] Tselios C, Bikiaris D, Maslis V, Panayiotou C. In situ compatibilization of polypropyleneepolyethylene blends: a thermomechanical and spectroscopic study. Polymer 1998;39(26):6807e17. [19] Vermeesch IM, Groeninckx G, Coleman MM. Macromolecules 1993;26:6643. [20] Porto MF, Rowe RVA, Santos O, Garcia CM, Taylor LT, Muniz EC, Rubira AF. Polyimides other high. Temp Polym 2001;1:1. [21] Roeder J, Oliveira RVB, Gonçalves MC, Soldi V, Pires ATN. Polypropylene/polyamide-6 blends: influence of compatibilizing agent on interface domains. Polym Test 2002;21(7):815e21. [22] Ramesh S, Leen KH, Kumutha K, Arof AK. FTIR studies of PVC/PMMA blend based polymer electrolytes. Spectrochim Acta Mol Biomol Spectrosc 2007;66(4e5):1237e42. [23] Ho CH, Wang CH, Lin CI, Lee YD. Synthesis and characterization of TPOePLA copolymer and its behavior as compatibilizer for PLA/TPO blends. Polymer 2008;49(18):3902e10.
Spectroscopic analysis of compatibilized polymer blends Ajay Vasudeo Rane, Sabana Ara Begum, Krishnan Kanny Composite Research Group, Department of Mechanical Engineering, Durban University of Technology, Durban, KwaZulu-Natal, South Africa
Abbreviations FTIR IR NMR PA6 PP LDPE PVC EVAL PMMA TPO DMAP SAAS PvPh PvAc MAH PVIm THF PLA
Fourier-transform infrared spectroscopy Infrared Nuclear Magnetic Resonance Polyamide 6 Polypropylene Low-density polyethylene Polyvinyl chloride Poly(ethylene-co-vinyl alcohol) Polymethyl methacrylate Thermoplastic polyolefin 4-dimethylaminopyridine Styrene-acrylic acid Poly(vinyl phenol) Poly(vinyl acetate) Maleic anhydride Poly (N-vinylimidazole) Tetrahydrofuran Polylactic acid
13.1 Introduction The internal structure of a material, simply called the structure, can be studied at various levels of observation. The degree of magnification required to study them by various methods is a measure of the level of observation. The details that are revealed or disclosed at a certain level of magnification are generally different from the details disclosed at some other level of magnification [1]. Depending on the level, the structure of materials can be classified as [1]: a. Macrostructure b. Microstructure Compatibilization of Polymer Blends ISBN 978-0-12-816006-0 https://doi.org/10.1016/B978-0-12-816006-0.00013-X
Copyright © 2020 Elsevier Inc. All rights reserved.
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Substructure Crystal structure Electronic structure Nuclear structure Macrostructure is the structure of a material as seen by the naked eye or low power magnification. It deals with the size, shape, and atomic arrangements in a crystalline material. The individual crystal in a polycrystalline material such as cast brass door knob is visible when polished and etched by constant contact with human hand and sweat. Similarly, large thin zinc crystal can sometimes be seen on the surface of heavily galvanized objects and they are called macroscopic. A macrostructure looks very similar to a sand grain and has more or less the same dimension [1]. Macrostructures may be studied either directly on the surface of the work (a casting, for example) or on a fracture or more frequently on specimens or samples cut out of large billets (ingots, forging, etc) or articles. And there are standard procedures available for macroexamination to reveal flaws and segregation in a material. Microstructure generally refers to the structure as observed under a microscope at magnification from 75 to 1500. A microstructure looks very similar to a dust particle. Microscopic examination reveals greater detail of the structure of a material but in almost every instance some sort of special specimen preparation and mounting is necessary [1]. Optical microscopes are employed to investigate the structure of materials and they enable only those details of the structure to be observed that are larger than 0.15 to 0.2 microns. Macrostructure and microstructure are two words relating to the same general type of phenomena and differ only in the degree of magnification required to study them. Substructure refers to structure obtained by using a microscope with a much higher magnification than optical microscope. And as such a wealth of new information on crystal imperfections such as dislocation and on very small particles of a few hundred angstroms in size is obtained and studied. At present, the electron microscope is used to study the substructure of the material and an effective magnification of 100,000 may be obtained [1]. Details of the object may be distinguished which are from 30 to 50A⁰ in size. The field ion microscope is a technique which produces images of individual atom. Crystal structure tells us the details of the atomic arrangement within a crystal, and it resembles a molecule. Electronic structure of a solid usually concerns the electrons in outer most shells of individual atoms that form the solid. Spectroscopic studies are very useful in determining the electronic c. d. e. f.
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structure. Nuclear structure is studied by nuclear spectroscopic techniques such as nuclear magnetic resonance and Mössbauer studies [1]. Analytical technique is one of the most powerful tools available for the study of atomic and molecular structure and is used in the analysis of most of the samples. Analytical technique or spectroscopy deals with the study of interaction of electromagnetic radiation with matter. During the interaction, the energy is absorbed or emitted by the matter. The measurements of this radiation frequency (absorbed or emitted) are made using spectroscopy [2]. The study of spectroscopy can be carried out under the following titles: Atomic spectroscopy and molecular spectroscopy. Atomic spectroscopy deals with interaction of electromagnetic radiation with atomsdatoms absorb radiation and get excited from ground state electronic energy level to another- and molecular spectroscopy deals with interaction of electromagnetic radiation with molecules, which results in transition between rotational, vibrational, and electronic energy levels. Likewise there are two spectrumsdabsorption spectrum and emission spectrum; when a molecule absorbs photon of energy and undergoes a transition from lower energy level to the higher energy level, the measurement of this decrease in intensity of radiation is the basis of absorption spectroscopy, the spectrum thus obtained is called absorption spectrum. If the molecule comes down from excited state to the ground state with the emission of photons of energy, the spectrum obtained is called emission spectrum [2]. Various spectroscopic techniques like infrared spectroscopy, nuclear magnetic resonance spectroscopy, electronic spectroscopy, mass spectroscopy, and conjoint spectroscopy have completely altered the face of organic chemistry. Most researchers will use infrared spectroscopy first, and nuclear magnetic resonance spectroscopy will follow; electronic spectroscopy is more limited in scope and mass spectroscopy in general the most expensive [3]. Spectroscopy should provide high-resolution, narrow line width spectra enhancing selectivity and structural information in case of polymers. Polymers and their systems (blends and composites) form multifaceted mixtures of structure and molecules, for which spectroscopic probe should selectively determine different structures at a point in time. It should have the ability to sense and detect very low levels of structure in the complex polymer systems, as minor structural changes effect physical and mechanical properties of polymeric systems. The spectroscopic probe should be specific in providing content information, in line with structure, form, and order of network in complex polymer system. The technique used for measurement must be nondestructive and noninvasive, so that polymer specimens can be
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evaluated by other characterization methods in addition to spectroscopic analysis. Polymer specimens are available in any useful (adhesive, film, coating, fiber, and film) form, and the probe should be able to study them. Majority of the spectroscopic analysis techniques do not satisfy the specifications of the spectroscopic probe for polymers. However, four spectroscopic techniques, Fourier transform infrared (FTIR), Raman, highresolution NMR spectroscopy of the solid state, and mass spectroscopy, fit into the criteria and these techniques are used individually or in combination, providing detailed structural information on polymers for purposes required, i.e., quality control or research and development [4]. Infrared spectroscopy is one of the most often and successfully implemented techniques used as spectroscopic tools for the study of polymers, i.e., structural determination. Infrared spectroscopy is a quick and thin-skinned method with easy sampling techniques, inexpensive instrumentation setup, easy and simple operation, in line with inexpensive service and maintenance. Interpretation of spectra is not complex, with ease in learning, although better discussion and interpretation is done by professionals. Although infrared spectroscopy is specific about the amount of certain structures in complex polymeric systems, quantitative measurements are still a challenge [4]. Raman spectroscopy and IR are complementary owing to differences in the selection rules which generate spectral information not available from IR. Most often, Raman spectroscopy is useful and advantageous when ease of sampling and remote sampling is required and in characterizing aqueous solutions. Apart from the abovementioned, Raman spectroscopy is used more as a research tool than an analytical tool for complex polymer systems due to ubiquitous fluorescence which occurs with polymer samples. Yet, remarkable improvement has been made recently due to which Raman spectroscopy is being used as tool for polymer characterizations [4]. Polymer blends are used for a range of applications with a motive to enhance the specific properties of individual homopolymers in the complex mixture. However, this complex mixture should be stable at molecular levels and become compatible. The stability of complex mixtures is dependent on individual properties of homopolymers in the polymer blend, degree of mixing, and physical and chemical interactions. Nearly all pairs of polymers are not miscible on a molecular level, resulting in phase separation, leading to decrement in mechanical properties. Determining glass transition temperature (Tg) confirms the presence of one polymer in the other polymer, i.e., coexisting phases, where shift of Tg takes place toward one of the polymer in complex polymeric systems. Single Tg is
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observed for amorphous polymer blends. Nature and reproducibility of interactions leading to compatibility, and changes involved with respect to time and temperature are important information in preparation of compatible blends. Even though thermoanalysis and NMR spectroscopy give information on the compatibility of blends, none of these techniques are favorable for quick examination of the kinetics of the phase separation process. On the other hand, FTIR spectroscopy is able to establish the nature and level of molecular interactions within polymer mixture and the change in these interactions with aging. Compatibility of a blend, in terms of IR, owes to the presence of a detectable ‘interaction’ spectrum that arises in comparison to the spectra of the two homopolymers involved in blending. In case of compatible polymers, an interaction spectrum with frequency shifts and intensity modifications that are fundamental to the system will be observed. For incompatible polymers, the spectrum is spectral sum, within experimental error, of the spectra of the two homopolymers involved in blending [4]. Interaction spectrum can be quantitatively determined by using factor analysis [5]. Observations in spectrum of polymer blends with varied volume fractions of individual polymer determine if interaction spectrum is a contributing factor. Further number of components in the blend spectra is evaluated by factor analysis. Three components are expected in case of compatible blends, and two for incompatible blends. Polymer blends [6] as a function of composition and temperature during solvent evaporation are studied and minimum indicator function values for both blends depict a three-component system, which means both blends are compatible. Double subtraction spectra of two homopolymers were used in determining the interaction parameter. Shift in frequencies and intensities in interaction spectrum indicate interaction between two homopolymers in polymer blend. Interaction spectra for polymer compositions, i.e., PVF2-PVAc heat treated at 75 and at 175 C are shown in Fig. 13.1A and B, respectively. Hydrogen bonds between the two components are the most IR observable molecular interactions [7]. Fig. 13.2 shows the IR spectra at room temperature for THF-casted poly(vinyl phenol) (PVPh)-PVAc blends containing varied quantity of PVAc in the regions from 3800 to 3000 cm1 and from 1800 to 1650 cm1 [8]. Carbonyl and hydrogen bonding IR regions have large spectral differences. Hydrogen bonding between polymeric chains results in frequency shifts and changes in band intensities indicating molecular interactions.
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Figure 13.1 (A) Interaction spectra of poly(vinylidene fluoride)-poly(vinyl acetate) (PVF2-PVAc) blends obtained immediately after heat treatment at 75 C for 1 h. Spectra were collected for blends having weight percent ratios of 10:90 to 90:10 PVF2-PVAc. (B) Interaction spectra of PVF2-PVAc blends heat treated at 175 C.
Figure 13.2 The IR spectra in the regions of 3800 and 1800 1650 cm1 recorded at room temperature of poly(4-vinylphenol)-poly(vinyl acetate) (PVAc) (PVPh-PVAc) blends cast from tetrahydrofuran containing 100 (a), 80 (b), 50 (c), 20 (d), and 0 (e) wt% PVAc.
Adding a small amount of comonomer into polymer mixtures that do not possess hydrogen bonding between each other, leads to compatibility, and acts as chemical links between the two homopolymers is an interesting method [9]. Fig. 13.3 shows the interaction spectrum (after double
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Figure 13.3 The IR spectra of styreneeacrylic acidepoly (methyl methacrylate) (SAASPMMA) (4:1) blend (A), pure SAAS (B), pure PMMA (C), and the interaction spectrum (AeBeC).
subtraction) for styrene (92%)eacrylic acid copolymer, the 89% styrenee acrylic acid (SAAS)epoly (methyl methacrylate) (PMMA) blend (4: 1), where hydrogen bonding has been introduced in the blends to make them compatible. Intermolecular interactions in NMR can be determined using crosspolarization, where carbons that are dipolar-coupled to protons provide 13 C resonances, whereas deuterated carbons will not provide any type of NMR signal except they are in close contact with protons on neighboring molecules. Cross-polarization is used to probe polymer mixtures and to study spatial order for mixtures of protonated and deuterated polymer blends [10]. Degree of mixing for processing aid is studied with deuterium approach [11]. Detailed information on protonated and deuterated carbons can be read in cited references [4]. Solid-state NMR is widely used to determine the miscibility in multicomponent polymer blends [12,13]. Conventionally, miscibility of polymers is characterized by locating glass transition temperature in a differential scanning calorimetry, wherein a single glass transition means miscible blend [14,15]. In NMR, identification via determining perturbation of the isotropic chemical shiftsetype of interactions, and if the specific interactions are due to hydrogen bonding, molecular complexes or chargeetransfer interactions can be identified. Triple 1H/13C/14N resonance experiment was used to evidence the presence of template complex formation in blends of poly-(methacrylic acid) (PMAA) and poly (N-vinylimidazole) (PVIm) [16]. Loss in spin echo
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intensity indicates a specific interaction between the carbonyl group of PMAA and the imidazole ring of PVIm, confirming formation of the polymer template complex in the polymer blend. NMR determines homogeneity in blends from molecular level to a few hundred A, wherein phase information is obtained on three different scalesdchanges in chemical shifts are monitored to get information on a molecular level. Blend possessing two different HT1s and two different HT1r indicates a single domain and sizes larger than about 500 A, one HT1r but H two T1s represent domain sizes ranging between 50 and 500 A. Only one H H T1r and one T1s indicate domain sizes smaller than about 50 A [16]. If proton relaxation times of the pure components show no significant differences, NMR method is limited to determine miscibility in polymer blends. Spin diffusion is also able to describe the heterogeneity in polymer blends [17]. Spin diffusion experiment classically consists of evolution stage generating initial polarization gradient between the components of the polymer blend; following a mixing stage, wherein time spin diffusion occurs and, finally, a detection stage for observing the follow-up 1H magnetization. Spin gradient can be generated based on mobility differences or on 1H chemical shift differences for polymer blends. Spin diffusion is governed by the dipolaredipolar interaction and for a dense rigid proton system. Spin diffusion rate is dependent on the space between nuclei as spin diffusion is restricted to molecules in vicinity. For occurrence of spin diffusion between two species they must be mixed closely on the molecular level. Useful semiquantitative information about domain size can be obtained [4] from the equation: ðr2 Þ ¼ 6Ds s where (r 2) is the mean square diffusive path length Ds is the spin-diffusion constant and is of order 4e7 1016 m2/s in the laboratory frame and half this magnitude in the rotating frame s is the time for a fundamental step in the random walk As HT1 is usually of the order of 7 101 s and HT1r of 102 s, the maximum diffusive path lengths range from 50 nm to about 2 nm, respectively. Single relaxation time will be observed if the two polymers in the blend are from two independent domains where the domain size is smaller than (r2), and two relaxation times when the domains are larger than (r2). Fig. 13.4B represents the carbonyl area spectrum of polymer blend along with the spectrum of maleic anhydride grafted polypropylene
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Figure 13.4 (A) Melt torque of low-density polyethylene/polypropylene 50/50 w/w blends: (a) without compatibilizer; (b) with 10 wt% compatibilizer (B) Fourier-transform infrared spectroscopy spectra of: (a) polypropylene-graft-maleic anhydride (PP-g-MA); (b) the product of reaction between PP-g-MA and poly(ethylene-co-vinyl alcohol).
copolymer. Characteristic peaks at 1863 and 1787 cm1 are ascribed to the five members saturated anhydride ring in grafted copolymer. While in spectra of polymer blends, they are attenuated and an occurrence of broad peak between 1750 and 1680 cm1 is noted. Maximum peak at 1727 cm1 is attributed to ester groups formed by the reaction shoulder at 1713 cm1 due to presence of carboxylic groups. Reaction between PP-g-MAH and EVAL (also took place in all PP/LDPE blends containing compatibilizer, as indicated in FTIR spectra). These results confirm that a reaction between maleic anhydride and hydroxyl groups definitely took place during blending, which increased while blending polymers as indicated in Fig. 13.4A. Adding compatibilizer improves mechanical properties of polymer blends. Tensile strength showed maximum value by adding 20 wt% compatibilizer, while impact strength enhancement was obtained by adding 10 wt% compatibilizer (see Fig. 13.5). Increased interfacial adhesion between the two polymers in their blends leads to better dispersion of the minor component into the matrix and increases the mechanical properties of polymer blends [18]. Raman spectra of PP and LDPE before blending were recorded as in Fig. 13.6A and B. Vibrations at 1105 and 810e860 cm1 are characteristic peaks of polypropylene and peaks at 1128 and 1062 cm1 are important peaks for polyethylene as illustrated in Fig. 13.6B. It was established that the spherical parts are PP and the continuous phase is LDPE, in view of the fact that their spectra are alike to those of the pure polymers (Fig. 13.6C). PP characteristic peaks were recorded at 1105 cm1 and at 810e860 cm1
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Figure 13.5 Low-density polyethylene/polypropylene blends for several compatibilizer contents: (a) 0 wt%, (b) 2.5 wt%, (c) 5 wt%, (d) 10 wt%, and (e) 20 wt%d(A) tensile strength, (B) elongation at break, and (C) impact strength.
(double peak, Fig. 13.6C-b) when probed at spherical domain. Additionally, peak at 2810e2950 cm1 when compared with the analogous peak of pure PP, it was confirmed that the spherical domains are polypropylene. Characteristic peaks of polyethylene at 1128 cm1 and at 1062 cm1 were present in flattened area surrounding spherical domains (Fig. 13.6C-a). Moreover, the double peak at 2820e2940 cm1 is similar as the analogous one in pure LDPE, which confirms the presence of polyethylene surrounding spherical domains of polypropylene and supports the intuitive rule from emulsions that in polymer blends the minor component forms the dispersed phase [18]. Characteristic peaks of both polymers exist in all areas in compatibilized blend (see Fig. 13.6D), as PP peaks dominate in continuous phase, whereas LDPE peaks are prominent in the small spherical domains (see Fig. 13.7). Characteristic peaks of LDPE at 1128 and 1062 cm1 appear with a very small intensity in spectra of spherical domains in uncompatibilized blend (Fig. 13.6E-c). As these peaks do not exist in the spectrum of pure PP, a conclusion that the two polymers show signs of a limited mutual solubility can be made. Intensity of two peaks increases, after
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Figure 13.6 Raman Spectra (A) pure polypropylene (PP) (B) pure low-density polyethylene (LDPE) (C) PP/LDPE 25/75 w/w blend focusing on: (a) spherical parts; (b) continuous phase (D) PP/LDPE 75/25 w/w blend focusing on: (a) continuous phase; (b) spherical domains (E) in the region 1200e950 cm1 of PP/LDPE blends: (a) pure PP; (b) pure LDPE; (c) spherical domains in PP/LDPE 25/75 w/w blend without compatibilizer; (d) spherical domains in PP/LDPE 25/75 w/w blend with 10 wt% compatibilizer (F) in the region 1200e750 cm1 of PP/LDPE blends: (a) pure PP; (b) pure LDPE; (c) flattened area in PP/LDPE 25/75 w/w blend with 10 wt% compatibilizer.
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Figure 13.7 Scanning electron image of fracture surface obtained from impact specimens (A) (a) 25/75 w/w, (b) 50/50 w/w, and (c) 75/25 w/w (B) polypropyleneelowdensity polyethylene (PPeLDPE) blends compatibilized with 10 wt% compatibilizer: (a) PP/LDPE, 25/75 w/w; (b) PP/LDPE, 50/50 w/w; (c) PP/LDPE, 75/25 w/w.
compatibilization (Fig. 13.6E-d) due to EVAL copolymer which is located at interface with maleic anhydride grafted polypropylene. Compatibilizer increases mutual solubility of the two polymers in polymer blend. Comparable annotations were made for the continuous phase. Characteristic absorption of polypropylene at 810e860 cm1 (weak, double peak) was made when flattened area around the PP domain was focused, as seen in Fig. 13.6F-c, which confirms the presence of polypropylene even in the flattened area surrounding the spherical domain [18].
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Micro-Raman spectroscopy seems to be an important tool for studying polymer blend morphology, as this has verified that PP and LDPE are immiscible with minor mutual solubility, allowing a clear detection of the dispersed phase in polymer blends [18]. Fig. 13.8 shows infrared spectra of: (a) PP (70)/PA6 (30) uncompatibilized blend showing a characteristic peak at 1640 cm1, for amide carbonyl group, and (b) represents compatibilized blend of the PP (60)/PA6 (30)/PP-g-MA (10) displaying three large peaks owing to the presence of imide linkages [19]. Imide group absorbances at 1779, 1726, and 1710 cm1 are recognized to in-phase, free, and hydrogen-bonded out-ofphase carbonyl vibrations, respectively; carbonyl stretch vibrations at 1774 and 1703 cm1 [15], and ring absorptions at 1775 and 1730 cm1 [20] are also noted by other group. In Gaussian deconvolution of the three large peaks in compatibilized blend (see inset in Fig. 13.8), the peak at 1764 cm1 represents carbonyl vibration of the imide group and 1710 cm1 to carbonyl vibration of the carboxylic acid from maleic anhydride grafted polypropylene unreacted. Predicted reaction is shown in Fig. 13.9. To make this predicted reaction clear, the PA6 domains were removed with formic acid. IR spectra of uncompatibilized blend without PA6 and compatibilized blend after PA6 extraction are shown in Fig. 13.10A and B, respectively. Fig. 13.10A shows only peaks assigned to
Figure 13.8 Infrared spectra of blends: (A) polypropylene (PP)/polyamide 6 (PA6) at 70/30 wt%; (B) PP/PA6/polypropylene-graft-maleic anhydride at 60/30/10 wt%. The insert shows a Gaussian deconvolution for the spectrum of the compatibilized blend in the range 1850 to 1600 cm1.
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Figure 13.9 Scheme of interface grafting by reaction between a carboxyl group of maleic anhydride and a polyamide amino end group.
Figure 13.10 Infrared spectra for the blend with polyamide 6 extraction: (A) uncompatibilized; (B) compatibilized.
PP molecules and confirms the nonexistence of interfacial interactions, while Fig. 13.10B exhibits absorbances at 1640 and 1730 cm1 due to carbonyl group and carbonyl imide linkage, in PA6 respectively. This discussion concludes the presence of the imide linkage at the interface of two polymeric components [21]. Table 13.1 gives the detail of peaks in PVC and PMMA in their pure form, as well as shifts in their peaks after blending. Fig. 13.11D is spectra of pure PVC, pure PMMA, and PVCePMMA blends. Peak at 1333 cm1 of pure PVC represents CH2 deformation, where relative intensity decreases PVC content decreases. Peak at 1254 cm1 is assigned to CH-rocking vibration. PVC when blended with PMMA forms small shoulder at the longer wavenumber. A doublet with increasing PMMA at 1271 and 1242 cm1 is observed. Relative intensity of the shoulder increases with increasing PMMA content. At 70% PMMA, the shoulder intensity is higher compared to that of the original band, confirming the complexation of PVCePMMA blends [22]. IR spectra of neat TPO and TPOeMAH are shown in Fig. 13.12A. Maleic anhydrideegrafted TPO shows new absorption peaks at 1864 cm1
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Table 13.1 Characteristics peaks in polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) and shifts in PVC/PMMA blends [22]. In PVC Shifts
2911 cm1 1333 cm1 1254 cm1 959 cm1 834 cm1 616 cm1
C H stretching CH2 deformation CH-rocking CH wagging CeCl stretching cis CH wagging
In PMMA 1
2951 cm 1721 cm1 1449 cm1 1159 cm1
1244 cm1 966 cm1 841 cm1 Shifts
CH stretching C O stretching CH3 stretching O CH3 stretching
1732 cm1 1435 cm1 1150 cm1
Figure 13.11 (A) Pure polyvinyl chloride (PVC) (B) pure polymethyl methacrylate (PMMA) (C) PVC: PMMA (30:70) blend (D) (a) pure PVC, (b) pure PMMA, (c) PVC: PMMA (70:30), (d) PVC: PMMA (50:50), and (e) PVC: PMMA (30:70) complexes.
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Figure 13.12 Fourier-transform infrared spectroscopy spectrum of (A) polylactic acid (PLA) and thermoplastic polyolefin (TPO)-derived copolymers (a) neat TPO; (b) maleic anhydrideemodified TPO; (c) TPOePLA copolymer; (d) neat PLA. (B) TPOePLA which was synthesized under various conditions (a) reaction temperature as variable; [TPO] 1 /4 10 wt%, [PLA] 1/4 20 wt%, [4’-Dimethylamino] 1/4 0.8 M. (b) 4-dimethylaminopyridine concentration as variable; [TPO] 1/4 10 wt%, [PLA] 1/4 20 wt%, reaction temp 1/4 140 C. (C) 1H nuclear magnetic resonance spectrum of TPOePLA copolymer. (D) Stressestrain curve of neat PLA and PLA/TPO blend.
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and 1786 cm1 related with the asymmetric and symmetric stretching of CO in the succinic anhydride units. Peak at 1786 cm1 corresponds to the maleic anhydride oligomeric segments in the functionalized polyolefin. Fig. 13.12A-c represents absorption peaks of PLAeTPO copolymer, with PLA carbonyl stretching at 1758 cm1; a set of characteristic absorptions in the fingerprint region of 1500e1000 cm1 were also present, like those of neat PLA displayed in Fig. 13.12A-d [23]. Infrared spectroscopy was used to determine the grafting ratio on PLA with respect to concentration of maleic anhydride and temperature of reaction. Peaks at 1786 cm1 and 1758 cm1 were observed and represented concentration of anhydride groups and PLA carbonyl stretching absorption in the TPOePLA copolymer, respectively. Decrease in absorption strength at 1786 cm1, broadening of carbonyl peak, and the appearance of absorption shoulder near 1758 cm1 as the reaction temperature increased were observed as shown in Fig. 13.12B-a, intensity of absorption at 1786 cm1 decreased as the DMAP concentration increased, but the PLA carbonyl absorption at 1758 cm1 intensified, indicating high reactivity of graft reaction at high temperature and DMAP concentration because more anhydride groups were consumed and more PLA chains were grafted. Esterification reaction of TPOeMAH with PLA, catalyzed by DMAP, was in line with a transesterification reaction, depolymerizing PLA. Mechanical properties of blends were higher than neat PLA [23].
13.2 Conclusion Infrared spectroscopy, qualitatively analyses starting materials, finished products, and the components in polymer blends. FTIR spectroscopy is reliable, fast, and cost-effective. In this chapter, analysis of IR spectra of typical polymer and polymer blends samples focused on identification of hydrogen bonding and miscibility in polymer blends. Solid-state NMR gives information on miscibility among polymers, with a precise ability to measure the length scales of mixing nearby by other experimental tools (i.e., traditional calorimetric methods), and to detect the inter- and intramolecular interactions responsible for miscibility in polymers. Raman microspectroscopy is attractive because the practical diffraction limit is on the order of the excitation wavelength than mid-IR spectroscopy which makes it possible to focus visible laser light to much smaller spot sizes (400 nm in air and 240 nm with an oil immersion objective) than may be characterized by mid-IR radiation.
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