A large stabilizing effect was obtained via adding titanium dioxide (TiO2) into poly (vinyl chloride)/α-methylstyrene-acrylonitrile copolymer/impact modifier blends. A comparison between photodegradation of blends (without TiO2) and composites (with TiO2) was conducted. Results of color difference, surface morphology, and thermogravimetric analysis tests indicated the higher UV resistance of composites than blends. Composites exhibited a almost unchangeable tensile strength and a certain retention rate of elongation at break; while drastic loss in these two properties were observed for blends. Fourier transform infrared and rheological tests also revealed the stabilizing effect exerted by TiO2, and it was found that different systems exhibited different stabilizing mechanisms. POLYM. COMPOS., 35:2365–2375, 2014. © 2014 Society of Plastics Engineers
Room temperature vulcanizing fluorosilicone rubbers (FSRs) were prepared from polydimethylsiloxane (PDMS), vinyl fluorosilicone-oil (VFS-oil), and precipitated silica (PDMS/VFS/SiO2). Rheological tests showed appropriate processing condition could be obtained when shear rate > 10 s−1. Mechanical tests indicated that tensile strength and elongation at break were not much affected by VFS-oil and no decline was observed after being aged in 70 °C ASTM 1# oil. The CF3 group could not only increase oil-resistance, but also decrease surface energy, which were proved by ATR-FTIR and contact angle tests. The PDMS oil immersion tests showed that the higher the content of VFS-oil, the better oil resistance can be obtained. The solvent-resistance tests indicated that the VFS-oil improved resistance to nonpolar/low-polar solvent. TGA results showed that the increasing content of VFS-oil could slightly decrease FSRs' thermal stability but increase FSRs' residual mass ratio at 790°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39708.
In this study, poly (vinyl chloride) (PVC)/α-methylstyrene-acrylonitrile-butadiene-styrene copolymer (AMS-ABS) (70/30)/chlorinated polyethylene (CPE) ternary blends was prepared. With the addition of CPE, it did not exert a negative influence in both the glass transition temperature and heat distortion temperature. Thermogravimetric analysis showed that addition of CPE did not play a negative role in the thermal stability. With regard to mechanical properties, high toughness was observed combined with the decrease in tensile strength and flexural strength. With the addition of 15 phr CPE, the impact strength increased by about 21.0 times and 8.5 times in comparison with pure PVC and PVC/AMS-ABS (70/30) blends, respectively. The morphology correlated well with the impact strength. It was also suggested from the morphology that shear yielding was the major toughening mechanisms for the ternary blends. And there existed a change in the fibril structures that are observed in scanning electron microphotographs. Our present study shows that combination of AMS-ABS and CPE improves the toughness without sacrificing the heat resistance, and the value of notched impact strength can be enhanced to the same level of super-tough nylon. POLYM. ENG. SCI., 54:378–385, 2014. © 2013 Society of Plastics Engineers
Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by solution casting. The crystallization behavior and hydrophilicity of ternary blends were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and contact angle test. According to morphological analysis, the surface was full of typical spherulitic structure of PVDF and the average diameter was in the order of 3 μm. The samples presented predominantly β phase of PVDF by solution casting. It indicated that the size of surface spherulites and crystalline phase had little change with the PMMA or PVP addition. Moreover, FTIR demonstrated special interactions among the ternary polymers, which led to the shift of the carbonyl stretching absorption band of PVP. On the other hand, the melting, crystallization temperature, and crystallinity of the blends had a little change compared with the neat PVDF in the first heating process. Except for the content of PVP containing 30 wt %, the crystallinity of PVDF decreased remarkably from 64% to 33% and the value of t1/2 was not obtained. Besides, the hydrophilicity of PVDF was remarkably improved by blending with PMMA/PVP, especially when the content of PVP reached 30 wt %, the water contact angle displayed the lowest value which decreased from 98.8° to 51.0°. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
This is a comparison study of the effects of various colloids on polydimethylsiloxane (PDMS) nanocomposites. Mica of layered structure and silica of nanospherical shape were both used with different content. Silane coupling agent was used for surface modification of mica to improve its dispersion. Wide X-ray diffraction patterns showed no intercalation during the incorporation of mica into PDMS matrix. Rheological characterization of the PDMS composites before curing showed that viscosities of PDMS-mica composites were much lower than that of PDMS composites with silica, particularly at low shear rates. Scanning electron microscope (SEM) suggested the existence of mica lamellar structure with high aspect ratio within the PDMS matrix. After vulcanization at room temperature, PDMS-mica composites could obtain mechanical properties close to that of PDMS composites with silica at same filler content. The cooperative effects of mica with silica showed that same mechanical properties of PDMS composites could be obtained at much lower viscosity, cost, and processing insecurity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
The photodegradation behavior of ethylene–octene copolymer (EOC) and EOC stabilized with UV stabilizers (Tinuvin 326, Chimassorb 81, Tinuvin 770 and Chimassorb 944) were investigated by the digital photography, color difference, gel content, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and mechanical tests. The results revealed that EOC exhibited a very poor photostability, whose performances were sharply reduced with increasing the irradiation time. The photodegradation products consisted of the carbonyl, hydroxyl and vinyl groups. The additives all showed an excellent photostabilizing effect, which effectively inhibited the gel formation and the chain photooxidation. The photostabilizing efficiency of these UV stabilizers could be ranked as Tinuvin 326 < Chimassorb 81 < Tinuvin 770 and Chimassorb 944. The secondary crystallization behavior was strongly affected by the annealing and chain scission. The chain scission, rather than the annealing, played a greater role in the secondary crystallization of the chain segments. And the serious chain scission could improve the mobility of the chain segments, which sharply promoted their crystallizability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
The photostability of hindered amine light stabilizer (HALS) and ultraviolet absorber (UVA) on the blends of plasticized poly (vinyl chloride) (PVC) and powder nitrile rubber (NBR) has been studied with a Xenon Test Chamber. The digital photos, color differences, attenuated total refection-Fourier transform infrared (ATR-FTIR) spectra and mechanical properties of the blends have been determined. HALS combined with UVA effectively protects PVC/NBR blends from yellowing and restrains the decrease of elongation at break of the blends. The synergistic phenomenon is ascribed to the different photostable mechanisms of HALS and UVA at different photo aging stages. The color of PVC/NBR control sample quickly changes into yellow at the first 400 h of irradiation, due to the polyenes structures that induced by the double bonds of butadiene in NBR. From 400 to 800 h, crosslinking dominates and the amount of polyenes decreases, resulting into the decrease of color change. At the early stage of irradiation, chain-scission of polymer takes the predominant place, and the tensile strength decreases. But during the latter stage, crosslinking takes the predominant place and the tensile strength increases slightly. HALS and UVA have a little effect on the maintaining of elongation at break of PVC/NBR blends. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers
Two kinds of piperidine derivatives including a low-molecular weight (Wt. 481, T770) and a high-molecular weight (Wt. 2000–3100, C944) hindered amine light stabilizers (HALS) are added singly or with ultraviolet absorbers (UVA) in combination to plasticized poly(vinyl chloride) (PVC) samples. Digital photos, color changes, attenuated total refection-Fourier transform infrared spectra (ATR-FTIR), and mechanical properties are obtained to investigate the photostable effect of the light stabilizers on the plasticized PVC after artificial aging. PVC samples with HALS perform well at the first 400 h of irradiation in color change, FTIR, and mechanical properties, but at the last 400 h the photostability decreases. Besides, C944 performs better than T770, because C944 is a high-molecular weight UV stabilizer and has good extraction resistance. Plasticized PVC samples with UVA resist discoloring and photooxidation from the photo-irradiation. Excellent synergism is observed between the combination of HALS and UVA. PVC with HALS/UVA performs better than PVC with HALS and PVC with UVA in color differences, FTIR, and mechanical properties. The synergism is due to the different stages of functions between HALS and UVA. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
In this study, tough and high heat-resistant poly (vinyl chloride) (PVC)/poly (α-methylstyrene–acrylonitrile) (α-MSAN) blends (70/30) containing acrylic resin (ACR) as a toughening modifier was prepared. With the addition of ACR, heat distortion temperature increased slightly, which corresponded with the increase in glass transition temperature measured by differential scanning calorimetry and dynamic mechanical thermal analysis. Thermogravimetric analysis showed that addition of ACR improved the thermal stability. With regard to mechanical properties, tough behavior was observed combined with the decrease in tensile strength and flexural strength. A brittle-ductile transition (BDT) in impact strength was found when ACR content increased from 8 to 10 phr. The impact strength was increased by 34.8 times with the addition of 15 phr ACR. The morphology correlated well with BDT in impact strength. It was also suggested from the morphology that microvoids and shear yielding were the major toughening mechanisms for the ternary blends. Our present study offers insight on the modification of PVC, since combination of α-MSAN and ACR improves the toughness and heat resistance of pure PVC simultaneously. Copyright © 2011 John Wiley & Sons, Ltd.
Ethylene–propylene–diene rubber (EPDM)/samarium borate (SmBO3)/ethylene-vinyl acetate (EVA) copolymer and EPDM/antimony-doped tin oxide (ATO)/EVA composites are aged at 150°C for different intervals. Surface modification is used to improve filler to matrix interphase. The main aim is to investigate the effect of filler type and vinyl acetate (VA) content in EVA on stability of EPDM composites. It is found that acidic ATO particles can lower pH level of EPDM composites and then promote the degradation of acetic acid during aging. Moreover, when VA content exceeds 14 wt %, the instable VA content causes more acetic acids escape during aging. With the increasing of aging time, EPDM/SmBO3 control and EPDM/SmBO3/EVA composites tend to become darker while EPDM/ATO and EPDM/ATO/EVA composites would become yellow. And the color change is correlated well with the variation of carbonyl index. The chemical crosslink points prevent crystals in EVA from melting at aging temperature (150°C), and the variation of crosslink density influences the crystallinity during aging. The tendency of tensile strength is well consistent with that of swelling ratios, and electric properties are correlated with increased polar groups and crystallinity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Photodegradation of plasticized poly(vinyl chloride) (PVC) stabilized by different thermal stabilizers including organic calcium complex and mercaptide organotin was investigated. Plasticized PVC sheets prepared by an open twin-roller mill and plate vulcanizing machine were exposed to xenon-arc light with the irradiance of 0.51 W/(m2·nm) at 65°C. A much better color stability displayed by mercaptide organotin than organic calcium complex has been confirmed by digital photos and color difference. This can be explained that the more effective mercaptide organotin minimizes the amount of thermal damage from processing thus favours subsequent UV weathering. Carbonyl index and decomposition activation energy (Ea1) obtained from attenuated total refection-Fourier transform infrared spectra (ATR-FTIR) and thermogravimetric (TG) analysis, respectively, further indicate that plasticized PVC sheets containing mercaptide organotin have more excellent UV resistance. Mechanical tests reveal that photodegradation of PVC is accompanied by the predominant process of chain scission on the surface of samples. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.
This study investigates the interaction of vinyl acetic (VA) content of ethylene-vinyl acetate (EVA), pH level of Samarium borate (SmBO3), and Sb-doped SnO2 (ATO) on reinforcement of peroxide-cured ethylene-propylene-diene rubber (EPDM)/SmBO3 and EPDM/ATO composites. It was found that EVA could both reinforce mechanical properties of EPDM, and enhance fluidity of gum during processing. During vulcanization, the interaction of VA groups and pH value of filler particles can influence the crosslink density of EPDM composites. In alkaline EPDM/SmBO3/EVA, VA groups could hydrolyze to produce polyvinyl alcohol and reduce pH level of medium by consuming OH−. When dispersed in acidic EPDM/ATO/EVA, VA groups could generate polyunsaturated bonds and acetic acid during vulcanization. The double bonds could react with dicumyl peroxide (DCP) and then boost crosslink efficiency of EPDM composites. Moreover, acetic acid and reduction of pH value could make DCP decompose into ions, and lower crosslink density of EPDM composites. In addition to the contribution of crosslink density, EVA could crystallize in EPDM composites to reinforce EPDM composites. Electric properties of EPDM were also affected. Surface and volume resistivity of EPDM composites decreased with the rise of VA content. As for EPDM/SmBO3/EVA composites, the growth of VA groups could boost dielectric constant and loss, decrease dielectric strength, due to the enhancement of polarity and reduction of crosslink density. In terms of EPDM/ATO/EVA composites, the EPDM/ATO/EVA14 possesses the highest dielectric constant and loss, and the lowest dielectric strength, because of the competing effect of VA content and crosslink density. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
Poly(vinylidene fluoride) (PVDF) chains with the same expanded state were obtained by dissolving PVDF resin in good solvent. Then, the crystallization of PVDF chains from mixed solvents composed of its good solvent and nonsolvent was investigated. N,N-dimethylformamide (DMF) and ethanol were used as good solvent and nonsolvent of PVDF, respectively. The crystalline phases of PVDF were characterized by Fourier transform infrared (FTIR) spectroscopy and wide angle X-ray diffraction (WAXD). For the crystallization of PVDF chains from mixed solvents, low ethanol content favored the formation of β phase, while high ethanol content resulted predominantly in the α phase. Different crystallization morphology was observed from the scanning electron microscopy (SEM) images. The obvious spherulite morphology disappeared with the increase in ethanol content in mixed solvent. According to thermal analyses, the crystallized PVDF from mixed solvents with high ethanol content had lower onset melting temperatures than that from low ethanol content. Smaller lamellar thickness calculated from WAXD data reasoned the low onset melting temperatures. The above results indicated that the crystallization of PVDF chains from mixed solvent was a “controlled” process by ethanol content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 575–581, 2010
The influence of relatively nontoxic thermal stabilizers including different types of organic calcium complex (Ca/Zn system of liquid stabilizers) and organotin on photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurement, viscosity-average molecular weight determination, UV–vis spectroscopy, Fourier transform infrared (FTIR), and thermogravimetric (TG) analysis. PVC films containing relatively nontoxic thermal stabilizers were prepared by solution casting and then exposed to xenon-arc light source with the irradiance of 0.51 W/(m2·nm) at 65°C. Two major chain processes, photodehydrochlorination and photo-oxidation, occur simultaneously during photodegradation of PVC. It has been confirmed by both color difference and UV–vis spectra that during the former 300 h of irradiation, organic calcium complex stabilizers retard photodehydrochlorination as well as initial color development of PVC films while organotin stabilizers remarkably accelerate photodehydrochlorination after 100 h. Relative carbonyl index (RCI) is first introduced to the analysis of FTIR results, which implies that organotin has a better ability to inhibit photo-oxidation than organic calcium complex and ensures longer stabilization time. The antioxidation of mercaptan organotin has been observed because it is an effective decomposer of peroxides and hydroperoxides. TG analysis reveals that some unstable structures generated due to the irradiation of ultraviolet can easily split away off from PVC macromolecular backbones under relatively low temperature. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers
Multiple melting behaviors and partial miscibility of ethylene-vinyl acetate (EVA) copolymer/low density polyethylene (LDPE) binary blend via isothermal crystallization are investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Crystallization temperature T (°C) is designed as 30, 50, 70, 80°C with different crystallization times t (min) of 10, 30, 60, 300, 600 min. The increase of crystallization temperature and time can facilitate the growth in lateral crystal size, and also the shift of melting peak, which means the completion of defective secondary crystallization. For blends of various fractions, sequence distribution of ethylene segments results in complex multiple melting behaviors during isothermal crystallization process. Overlapping endothermic peaks and drops of equilibrium melting points of LDPE component extrapolated from Hoffman–Weeks plots clarify the existence of partial miscibility in crystalline region between EVA and LDPE. WAXD results show that variables have no perceptible influence on the predominant existence of orthorhombic crystalline phase structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
The role of the single diluents and mixed diluents on the poly (vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend membranes via thermally induced phase separation (TIPS) process was investigated. The crystallization behaviors of PVDF in the diluted samples were examined by differential scanning calorimetry. The melting and crystallization temperatures of those diluted PVDF blend were decreased with the enhanced interactions between polymer chains and diluent molecules. The crystallinity of PVDF in the diluent was always higher than that obtained in PVDF blend sample. This can be explained by the dilution effects, which increased the average spatial separation distances between crystallizable chains. Thus, the PVDF crystallization was favored. Additionally, solid-liquid (S-L) phase separation occurred in the quenched samples. Illustrated by scanning electron microscopy, inter- and intraspherulitic voids were formed in the ultimate membranes, which related to the polymer/diluent interactions, the kinetics of crystallization and diluent rejection from the growing crystal. The porosity of the PVDF blend membranes obtained from the mixed diluents was higher than those obtained from the single diluent samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
The aim of this investigation is to evaluate the effect of damp-heat aging on properties of ethylene-vinyl acetate (EVA) copolymer (14 wt % vinyl acetate units), ethylene-acrylic acid (EAA) copolymer (8 wt % acrylic acid units) and their blends. Attenuated total reflection Fourier transform infrared spectrum (ATR-FTIR), differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD), and mechanical tests are employed to investigate the changes of copolymer blends' structures and properties. ATR-FTIR tests show that increase of carbonyl index is owing to the incorporation of oxygen into the polymeric chain of EVA in the blends and has not much influence on the EAA. By DSC measurements, the low temperature endothermic peak (Tm2) of various EAA/EVA blends at about 43.7°C attributed to the secondary crystallization is increased with the aging time, which means the lamellar thickness of low temperature crystallite is increased. The increase of low temperature peaks probably derives from the interphase or even amorphous parts of both EVA and EAA components. The crystalline size detected by WAXD and degree of crystalline have both been improved by damp-heat aging. By mechanical tests, the sample has more hardness, more modulus at 100% extension ratio, more tensile strength with less elongation at break as the proportion of EAA increase. Aging influence will induce deterioration of mechanical properties, and increase of degree of crystallinity can make the hardness, the modulus at 100% extension ratio and tensile strength increase. The two factors will both have effect on the mechanical properties of EAA/EVA blends. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
The aim of this investigation is to evaluate the effect of hot air aging on properties of ethylene-vinyl acetate copolymer (EVA, 14 wt % vinyl acetate units), ethylene-acrylic acid copolymer (EAA, 8 wt % acrylic acid units), and their blends. Attenuated total reflection-Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), wide angle X-ray diffraction, and mechanical tests are employed to investigate the changes of copolymer blends' structures and properties. Increase of carbonyl index derived from ATR measurements with aging time suggests the incorporation of oxygen into the polymeric chain. By DSC measurements, the enthalpy at low temperature endothermic peak (Tm2) of EAA becomes less and disappears after 8 weeks aging, but enthalpy at Tm2 of EVA is not influenced by the hot air aging and remains stable despite of the aging time. For various proportions of EAA and EVA blends, enthalpy at Tm2 decreases as the EAA proportion increases when aging time is 8 weeks; after several weeks of hot air aging, the various blends appear a same new peak just over the aging temperature 70°C which is due to the completion of crystals which are not of thermodynamic equilibrium state. Mechanical tests show that increase of crystallinity and hot air aging deterioration both have influence on the hardness, tensile strength, and elongation at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
We reported herein the damp-heat aging of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate (VAc) contents simultaneously for weeks. The aging was carried out under temperature of 40°C and relative humidity of 93% in air atmosphere. The changes of copolymers' structures and properties were investigated by means of FTIR, wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) and mechanical tests. CI values derived from ATR-FTIR spectra have a decrease when aging time is 1 week and then increase during damp-heat aging process which suggests the first loss then incorporation of OC group. WAXD infer that the narrowing trend of FWHM and increase of crystal sizes may attribute to the melting and re-crystallization of secondary crystallization, which is also confirmed by DSC results. Mechanical tests including Shore A and Shore D hardness, modulus at 100%, tensile strength and elongation at break, are all depending on the primary crystallization and influenced little by damp-heat aging. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Poly(vinylidene fluoride) (PVDF) blend microporous membranes were prepared by PVDF/poly(methyl methacrylate) blend (with mass ratio = 70/30) via thermally induced phase separation. Benzophenone (BP) and methyl salicylate (MS) were used as diluents. The phase diagram calculations were carried out in terms of a pseudobinary system, considering the PVDF blend to be one component. The crytallization behaviors of PVDF in the dilutions were detected by differential scanning calorimetry measurement. In these two systems, the melting and crystallization temperatures leveled off in the low polymer concentration (<40 wt %), but shifted to a higher temperature when the polymer concentration >40 wt %. The calculated crystallinity of PVDF for samples with low polymer concentrations was greater than those with high polymer concentrations, because of the limited mobility of polymer chains at a high polymer concentration. The membrane structure as determined by scanning electron microscopy depended on the phase separation mechanism. The quenched samples mainly illustrated the occurrence of crystallization on the same time scale as the liquid–liquid phase separated, resulting in the obvious spherulitic structure with small pores in the spherulites. As the polymer concentration increased, the size of the spherulites and pores within the spherulite was decreased. The evaluated porosity for BP diluted system was higher than that for MS diluted system, and decreased with the increased polymer concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 248–260, 2009
The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N,N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.
The dependence of surface structure of the poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) films by solution casting on properties of seven substrates was investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). It was revealed that the polyblend films obtained by casting onto each substrate contained exclusively β phase PVDF. Higher crystallinity of the film was obtained by casting onto ceramic, polytetrafluoroethylene (PTFE), copper (Cu), stainless steel and glass substrates than that by casting onto aluminium (Al) and polypropylene (PP) substrates, depending on the degree of close lattice matching. The surface crystalline structure of PVDF was strongly affected by the wettability of substrate. The largest size of PVDF spherulitic crystal structure with about 6 μm presented in the casting film grown at the air/solution interface on glass substrate, while the smallest spherulite size with about 3 μm was generated by casting onto PTFE, stainless steel and PP substrates. It implied that the higher surface tension the substrate had, the larger PVDF spherulite grew at the air/solution interface.
The effect of diluents on polymer crystallization and membrane morphology via thermally induced phase separation(TIPS) were studied by changing the composition of the mixed-diluents systematically, in the system of poly(4-methyl-1-pentene) (TPX)/dibutyl-phthalate (DBP)/di-n-octyl-phthalate (D-n-OP) with TPX concentration of 30 wt %. The TPX crystallization was observed with differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The membranes were characterized with scanning electron microscopy (SEM), porosity, and pore size measurement. As the content of D-n-OP increased in mixed-diluents, the solubility with TPX increased, inducing the phase separation changing from liquid–liquid phase separation into solid–liquid phase separation, which changed the membrane morphology and structure. When the ratios of DBP to D-n-OP were 10 : 0, 7 : 3; 5 : 5, and 3 : 7, membranes were formed with cellular structure and well connected pores, while the ratio was 0 : 10, discernable spherulities were found with not well-formed pore structure. The effect of composition of the mixed-diluents on membrane morphology was more remarkable in TPX/dioctyl-sebacate (DOS)/dimethyl-phthalate (DMP) system, since good cellular structure was formed when the ratios of DOS to DMP were 10 : 0, 7 : 3, while spherulites were observed when 5 : 5. Dual endotherm peaks behavior on DSC melting curves emerged for all the samples in this study, which was attributed to the special polymer crystallization behavior, primary crystallization, and secondary crystallization occurred when quenching the samples. As the content of D-n-OP increased, the secondary crystallization enhanced which induced the first endotherm peak on DSC melting curves moving to a lower temperature and the broadening of the overall melting peak, as well as the increasing of the overall crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The influence of ultraviolet (UV)-irradiation on the photodegradation mechanism of different average degrees of polymerization (DP) of poly(vinyl) chloride (PVC) with UV-irradiation time was investigated by viscosity-average molecular weight determination, UV-vis spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and scanning electron microscopy (SEM). PVC films with different DP (800, 1000, 1300, 3000) were prepared by solution casting. It was carried out exposing specimens to a xenon-arc light source with a spectral irradiance of 0.68 W/(m2 ·nm) at 63°C. It was found that the photodegradation mechanism of the lower DP of PVC (DP = 1000) was different from the higher DP of PVC (DP = 3000). This was because the lower DP of PVC was a homopolymer, while the higher DP of PVC was often produced by copolymerizing with a certain quantity of crosslinking agent (e.g., DAP and DAM). UV-vis and FTIR spectroscopy studies provided some results concerning the structure of the irradiated PVC, and the carbonyl index and CCl index were induced to study the process of PVC photodegradation with different DP. TGA showed that the degradation temperatures of different weight loss increased with the irradiation time. The surface morphology of the irradiated polymer films with different DP was observed by contact angle measurement and SEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Films of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend were derived from a special procedure of casting semi-dilute solutions. Hydrophilic character and crystallization of PVDF were optimized by variation of PMMA concentration in PVDF/PMMA blends. It was found that a PVDF/PMMA blend containing 70 wt% PMMA has a good performance for the potential application of hydrophilic membranes via thermally induced phase separation. The films presented β crystalline phase regardless of PMMA content existed in the blends. Thermal analysis of the blends showed a promotion of crystallization of PVDF with small addition of PMMA which induced larger lamellar thickness of PVDF, leading to the largest spherulitic crystal of PVDF (10 wt% PMMA) is about 8 μm. SEM micrographs illustrated no phase separation occurred in blends, due to the high compatibility between PVDF and PMMA.
The effects of the polymer concentration and quenching temperature on the phase separation, the membrane morphology and polymer crystallization behavior in a poly(4-methyl-1-pentene) (TPX)-dioctylsebacate (DOS)-dimethylphthalate (DMP) system via thermally induced phase separation were studied with a pseudobinary phase diagram, with the weight ratio of DOS:DMP = 1:1. SEM was used to observe the membrane morphology and structure, whereas the TPX crystallization behavior was studied with DSC and WAXD. Liquid-liquid phase separation occurred, although quenching under the crystallization temperature. As the quenching temperature decreased, the pore size decreased, with better connected pore structure formed. The membranes quenched at 333 and 363 K showed good cellular structures, with an average pore size of about 2.3μm, whereas the pores of the membranes quenched at 393 and 423 K were not well formed, with some lamellar crystals on the inner side. The diluent assisted the mobility of the polymer chain, which improved the polymer crystallization. Dual-melting-peak behavior occurred for all the samples studied here. As the quenching temperature increased, the first peak of the melting trace moved to a higher temperature, whereas the second one stayed almost the same. The flexibility of the TPX main chain was restricted by the side groups, which allowed liquid-liquid phase separation to occur first when quenched below the equilibrium crystallization temperature. This allowed primary and secondary crystallization, which was responsible for the dual-melting-peak behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 153–161, 2007
Ternary blends of polypropylene (PP), a polypropylene-grafted acrylic acid copolymer (PP-g-AA), and an ethylene–acrylic acid copolymer (EAA) were prepared by melt blending. The surfaces of films with different contents of these three components were characterized with contact-angle measurements. Scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis were used to characterize the microstructure, melting and crystalline behavior, and thermal stability of the blends. The contact angles of the PP/PP-g-AA blends decreased monotonically with increasing PP-g-AA content. With the incorporation of EAA, the contact angles of the PP/PP-g-AA/EAA ternary blends decreased with increasing EAA content. When the concentration of EAA was higher than 15 wt %, the contact angles of the ternary blends began to increase. Scanning electron microscopy observations confirmed that PP-g-AA acted as a compatibilizer and improved the compatibility between PP and EAA in the ternary blends. Differential scanning calorimetry analysis suggested that acrylic acid moieties could act as nucleating agents for PP in the polymer blends. Thermogravimetric analysis and differential thermogravimetry confirmed the optimal blend ratio for the PP/PP-g-AA/EAA ternary blends was 70/15/15. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 436–442, 2006
Poly(ethylene-vinyl acetate) (EVA) copolymer was melt grafted with maleic anhydride (MAH) in a twin screw extruder in the presence of peroxide. It is confirmed that MAH has been melt grafted on the backbone of EVA by FTIR using the method of hydrolysis. The NMR analysis suggests that the grafting reaction occurs on the tertiary carbon of main chain of EVA other than the methyl moiety of vinyl acetate (VA) group. The incorporation of VA groups onto the matrix shows a competitive effect on the grafting. The existence of VA groups promotes the extent of MAH graft onto EVA; nevertheless, it also weakens the crystallizability of main chain. When the content of peroxide initiator is 0.1 wt % based on the polymer matrix, the grafting degree increases with increasing the concentration of monomer. When the peroxide content is higher than 0.1 wt %, side reactions such as crosslinking or disproportionation will be introduced into this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 841–846, 2006
The crystallization behavior of PVDF (poly (vinylidene) fluoride) in PVDF-dimethylphthalate(DMP) system was investigated in the liquid–liquid (L–L) phase separation region, solid–liquid (S–L) phase separation region and different quenching conditions via thermally induced phase separation (TIPS). Differential scanning calorimetry (DSC) indicated the crystallinity of PVDF in PVDF-DMP system increased in the early stage of phase separation and polymer-rich phase crystallized completely in the late stage of phase separation. The scanning electron microscopy (SEM) showed the different quenching temperatures had effects on the spherulite size of polymer rich phase and the ultimate membrane structure in the different phase separation regions. The wide angle X-ray diffraction (WAXD) was used to quantify the crystal structure of PVDF in PVDF-DMP system. The α-phase PVDF was obtained when the system quenched to different temperatures above 40°C, and the area of diffraction peaks changed when quenching temperatures changed. While the β-phase PVDF was formed when PVDF-DMP system was quenched form liquid nitrogen and crystallized for 24 h in 25°C water bath. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3714–3719, 2006
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