Study on crystal process and isothermal crystallization kinetics of UHMWPE/CA‐MMT composites

Changes in the crystal morphology, crystallinity, and the melting process of thermoplastics resulted in significant changes in the processability and mechanical behavior of composites. In our former study, we prepared a novel antibacterial UHMWPE/CA‐MMT composite. In this study, the crystal process and crystallization kinetics of pure UHMWPE, UHMWPE/MMT, UHMWPE/CA, and UHMWPE/CA‐MMT were characterized by differential scanning calorimeter (DSC). The results showed that the chlorhexidine acetate (CA) and montmorillonite (MMT) could cause strong heterogeneous nucleation. The results of crystallization kinetics indicated that the addition of CA could decrease the crystallization rate constant K value and widen the range of the crystal growth temperature. The reological behaviors of four samples were carried out by a physical MCR301 rheometer. The results showed that the CA could bring down the complex viscosity of composites, thus affecting the crystal process or crystallization kinetics. POLYM. COMPOS., 33:1987–1992, 2012. © 2012 Society of Plastics Engineers     

Freeze‐drying method prepared UHMWPE/CNTs composites with optimized micromorphologies and improved tribological performance

Uniformly dispersed carbon nanotubes (CNTs) reinforced ultrahigh molecular weight polyethylene (UHMWPE) composites were successfully prepared by freeze‐drying method. Specifically, polymer powders were mixed with CNT aqueous paste, and then freeze‐dried. As a consequence, CNTs covered at the surface of UHMWPE powders evenly when CNT content was not very high, which improved the quantity of crystals and crystallinity of UHMWPE/CNTs composites by providing more nucleation sites during the upcoming compression‐molded process. Furthermore, optimized dispersion state of CNTs and concomitant higher crystallinity made freeze‐drying technique prepared composites display much lower wear rate when compared with pure UHMWPE and UHMWPE/CNTs composites fabricated by common heat‐drying method. In a word, our proposed method of freeze‐drying is simple and effective for mass production of UHMWPE/CNTs composites, and it is promising to be applied to fabricate many kinds of nanofillers modified polymer composites, for example, polymer/graphene material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41885.     

Influence of shape and surface modification of nanoparticle on the rheological and dynamic‐mechanical properties of polyamide 6 nanocomposites

Nanocomposites of polyamide 6 (PA6) with different concentrations of silane‐treated, organic‐treated, and nontreated nanoparticles of halloysite (HNT) and montmorillonite (MMT) had their microstructure and melt and solid state rheological behavior analyzed. The microstructure analysis was done using transmission electron microscopy (TEM) and wide angle X‐ray diffraction (WAXD); the effectiveness of the silanization was studied by thermogravimetric analysis (TGA) and Fourier transform infrared. It was found that exfoliation occurred in the organic‐treated MMT, but not in the silane‐treated MMT and that silanization was small in the HNT nanoparticles (due to its low amount of surface hydroxyls groups). Steady state shear, small amplitude oscillatory, and transient tests also indicated that: (i) only the nanocomposites with organic‐treated MMT, at concentrations above the theoretical percolation threshold developed a percolated network; (ii) the silane treatment increased the shear elastic modulus (G) of the PA6/HNT nanocomposites in the solid state, but not of the PA6/MMT; (iii) the organic‐treated MMT formed composites with the highest G, as expected. Thus, it was concluded that the HNT nanoparticles had a high potential as nanofiller for PA6, but further research on more efficient compatibilizers for HNT is still needed. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Synthesis and characterization of polyurethane cationomer/MMT hybrid composite

BACKGROUND: The development of polymeric nanocomposites incorporating intercalated or exfoliated layered silicate clays into the organic matrix has been substantially motivated by the significant improvements induced by the presence of the inorganic component. Moreover, understanding and controlling the dispersion of inorganic layers into segmented polyurethane matrices by means of ionic interactions, and exploiting these interactions to enhance physicomechanical behaviour, could be of great interest in the field of polymer nanocomposites. RESULTS: New cationic polyurethane elastomers were prepared starting from poly(butylene adipate)diol (M_n = 1000 g mol^?1), 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol and N‐methyldiethanolamine or N,N′‐β‐hydroxyethylpiperazine, used as potential quaternizable moieties. The characterization of the polymers was achieved using specific analyses employed for the macromolecular samples (Fourier transform infrared and ¹H NMR spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography). An extension of our research on polymers reinforced with organically modified montmorillonite (OM‐MMT) in order to prepare hybrid composites with improved properties was performed and the resulting materials were characterized using TGA, X‐ray diffraction, atomic force microscopy and scanning electron microscopy. Also, the mechanical properties of the cationic polyurethane/OM‐MMT composites were investigated in comparison with the pristine ionic/non‐ionic polymers and their composites containing non‐ionic polymer blended with OM‐MMT or ionic polymer and unmodified MMT. CONCLUSION: The insertion of the organically modified clay into the polymeric matrix gave an improvement of the mechanical properties of the polyurethane composites, especially the tensile strength and stiffness of the hybrid materials. Copyright © 2009 Society of Chemical Industry     

Rheology of poly(propylene)/clay nanocomposites

The linear and nonlinear shear rheological behaviors of poly(propylene) (PP)/clay (organophilic‐montmorillonite) nanocomposites (PP/org‐MMT) were investigated by an ARES rheometer. The materials were prepared by melt intercalation with maleic anhydride functionalized PP as a compatibilizer. The storage moduli (G′), loss moduli (G″), and dynamic viscosities of polymer/clay nanocomposites (PPCNs) increase monotonically with org‐MMT content. The presence of org‐MMT leads to pseudo‐solid‐like behaviors and slower relaxation behaviors of PPCN melts. For all samples, the dependence of G′ and G″ on ω shows nonterminal behaviors. At lower frequency, the steady shear viscosities of PPCNs increase with org‐MMT content. However, the PPCN melts show a greater shear thinning tendency than pure PP melt because of the preferential orientation of the MMT layers. Therefore, PPCNs have higher moduli but better processibility compared with pure PP.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2427–2434,2004     

The effects of hybrid fillers on thermal,mechanical, physical,and antimicrobial properties of ultrahigh‐molecular‐weight polyethylene‐reinforced composites

The effects of hybrid filler of zinc oxide and chitosan (chitosan–ZnO) on thermal, flexural, antimicrobial, chemical resistance, and hardness properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) composites with varying concentration of zinc oxide (ZnO) and further hybridized by chitosan (CS) were successfully studied. The composites were prepared using mechanical ball milling and followed by hot compression molding. The addition of ZnO to the UHMWPE matrix had lowered the melting temperature (T _m) of the composite but delayed its degradation temperature. Further investigation of dual filler incorporation was done by the addition of chitosan to the UHMWPE/ZnO composite and resulted in the reduction of UHMWPE crystallization. The flexural strength and modulus had a notably high improvement through ZnO addition up to 25 wt% as compared to neat UHMWPE. However, the addition of chitosan had resulted in lower flexural strength than that of 12 wt% ZnO UHMWPE composite but still higher than that of neat UHMWPE. It was experimentally proven that the incorporation of ZnO and chitosan particles within UHMWPE matrix had further enhanced the antimicrobial properties of neat UHMWPE. Chemical resistance was improved with higher ZnO content with a slight reduction of mass change after the incorporation of chitosan. The hardness value increased with ZnO addition but higher incorporation of chitosan had lowered the hardness value. These findings have significant implications for the commercial application of UHMWPE based products. It appears that these hybrid fillers (chitosan–ZnO)‐reinforced UHMWPE composites exhibit superior overall properties than that of conventional neat UHMWPE. POLYM. COMPOS., 38:1689–1697, 2017. © 2015 Society of Plastics Engineers     

Improvement of the tribological behavior of ultra‐high‐molecular‐weight polyethylene by incorporation of poly (phenyl p‐hydroxyzoate)

Ultra‐high‐molecular‐weight polyethylene/poly (phenyl p‐hydroxyzoate) composites (coded as UHMWPE/PPHZ) were prepared by compression molding. The effects of the poly (phenyl p‐hydroxyzoate) on the tribological properties of the UHMWPE/PPHZ composites were investigated, based on the evaluations of the tribological properties of the composites with various compositions and the examinations of the worn steel surfaces and composites structures by means of scanning electron microscopy and transmission electron microscopy. It was found that the incorporation of the PPHZ led to a significant decrease in the wear rate of the composites. The composites with the volume fraction of the PPHZ particulates within 45% ～ 75% showed the best wear resistance. The friction coefficient of the UHMWPE/PPHZ composites decreased with increasing load and sliding velocity, while the wear rates increased with increasing load. This was attributed to the enhanced softening and plastic deformation of the composites at elevated load or sliding velocity. The UHMWPE/PPHZ composites of different compositions had differences in the microstructures and the transfer film characteristics on the counterpart steel surface as well. This accounted for their different friction and wear behaviors. The transfer film of the UHMWPE/PPHZ composites appeared to be thinner and more coherent, which was largely responsible for their better wear resistance of t composite than the UHMWPE matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2336–2343, 2005     

Grafting of hydrophilic monomers onto aminopropyl‐functionalized sodium montmorillonite via surface‐initiated redox polymerization

Hydrophilic polymer/sodium montmorillonite (Na‐MMT) hybrid nanomaterials were prepared via surface‐initiated redox polymerization of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (PAMPS‐g‐MMT), acrylamide (PAAm‐g‐MMT) and styrenesulfonic acid sodium salt (PSSA‐g‐MMT) from surface of aminopropyl‐functionalized sodium montmorillonite (AMMT) dispersed in an aqueous medium. Cerium(IV) ammonium nitrate/nitric acid and aminopropyl groups on the surface of AMMT were used as oxidant and reducing groups, respectively. AMMT was prepared by covalently attaching 3‐aminopropyltriethoxysilane onto the surface of Na‐MMT. Hydrophilic monomers (AMPS, AAm and SSA) were then grafted onto AMMT dispersed in water via redox initiation at 40 °C. Structure, morphology and thermal properties of the AMMT, PAMPS‐g‐MMT, PAAm‐g‐MMT and PSSA‐g‐MMT hybrid materials were characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD) and thermogravimetric (TGA) analyses, respectively. FTIR results indicated that hydrophilic monomers were successfully grafted onto the surface of MMT. Grafting amounts of the hydrophilic polymers were estimated from TGA thermograms to be 28.8, 118.8 and 14.4% for PAMPS, PAAm and PSSA, respectively. XRD patterns showed an exfoliated morphology for PAMPS‐ and PAAm‐grafted MMT hybrid nanomaterials and an intercalated/exfoliated morphology for the PSSA‐grafted MMT one. The effect of the nature of hydrophilic monomer on the grafting efficiency is discussed in detail. © 2013 Society of Chemical Industry     

Synthesis,Characterization and Properties of Nitropolybutadiene as Energetic Plasticizer for NHTPB Binder

The nitration of low molecular weight polybutadiene (PB) by a convenient and inexpensive procedure was investigated. To retain the unique physico‐chemical properties of the plasticizer, it was nitrated to an extent of 10 % double bonds. The product nitropolybutadiene (NPB) was characterized by FT‐IR and ¹H NMR spectroscopy as well as GPC, DSC, and TGA methods. The kinetic parameters for the decomposition of NPB from room temperature to 400 °C were obtained from non‐isothermal DSC. The changes in glass transition temperature (T _g) and inert uncured binder systems were used for determination of its efficiency as plasticizer. NPB was used in cured and unfilled nitro‐hydroxyl terminated polybutadiene (NHTPB) binder. Isothermal thermogravimetric analysis (Iso‐TGA) was employed to determine the migration rate in cured and unfilled HTPB binder systems compared to the dioctyladiphate (DOA) plasticizer. It was found that the exudation of the NPB plasticizer is slower than that of the DOA plasticizer. Thus, the NHTPB/NPB binder system (binder/plasticizer) presents more convenient mechanical properties than HTPB/DOA and is a promising new energetic binder system for polymer bonded explosives.     

Preparation of chitosan‐g‐poly(acrylamide)/montmorillonite superabsorbent polymer composites: Studies on swelling,thermal, and antibacterial properties

Superabsorbent composites based on chitosan‐g‐poly(acrylamide) and montorillonite (CTS‐g‐PAAm/MMT) were synthesized through in situ radical polymerization by grafting of crosslinked acrylamide onto chitosan backbone in presence of MMT at different contents. The formation of the grafted network was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). The obtained porous structure was observed by scanning electron microscope (SEM). The presence of clay and its interaction with chitosan‐g‐poly(acrylamide) (CTS‐g‐PAAm) matrix was evidenced by ATR‐FTIR analysis. The morphology was investigated by both X‐ray diffraction (XRD) and SEM analyses. It was suggested the formation of mostly exfoliated structures with more porous structures. Besides, the thermal stability of these composites, observed by TGA analysis, was slightly affected by the clay loading as compared to the matrix. These hydrogel composites were also hydrolyzed to achieve anionic hydrogels with ampholytic properties. Swelling behaviors were examined in doubly distilled water, 0.9 wt % NaCl solution and buffer solutions. The water absorbency of all superabsorbent composites was enhanced by adding clay, where the maximum was reached at 5 wt % of MMT. Their hydrolysis has not only greatly optimized their absorption capacity but also improved their swelling rate and salt‐resistant ability. The hydrolyzed superabsorbent showed better pH‐sensitivity than the unhydrolyzed counterparts. The results of the antibacterial activity of these superabsorbents composites against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), assayed by the inhibitory zone tests, have showed moderate inhibition of the bacteria growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39747.     

Influence of organic montmorillonite nanoparticles on the microstructures and thermal and tribological properties of polyethersulfone and polytetrafluoroethylene composites

Because of high wear rate and low thermal deformation temperature, the generalization and application of polytetrafluoroethylene (PTFE) in the field of tribology is restrained to a certain extent. In order to improve the wear resistance and thermal stability of this self‐lubricating polymer, organic montmorillonite (OMMT) nanoparticle reinforced polyethersulfone (PES) and PTFE ternary composites were prepared by the cold molding and vacuum sintering technology. The effects of sodium montmorillonite (Na‐MMT) and OMMT on the microstructures, thermal stabilities and tribological properties of PTFE composites were comparatively studied. The results show that the thermal stability of the PES/PTFE composites is clearly improved by the incorporation of OMMT nanoparticles. Not only the friction coefficients but also the wear rates of OMMT/PES/PTFE composites are less than those of Na‐MMT/PES/PTFE composites under identical tribological tests. Of all these PTFE composites, the PES/PTFE composite containing 10.0 wt% OMMT nanoparticles exhibits the best friction and wear properties (μ = 0.14, k = 5.78 × 10^?15 m³ N^–1 m^?1). This can be attributed to the existence of a polymer multicomponent layer consisting of PTFE, PES and OMMT on the composite surface as well as the formation of uniform PTFE transfer film on the worn surfaces of metal counterparts.     

Effect of polyethylene‐graft‐maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh‐molecular‐weight polyethylene/copper composites

Ultrahigh‐molecular‐weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X‐ray photoelectron spectroscopy. The incorporation of PE‐g‐MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE‐g‐MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh‐molecular‐weight‐polyethylene‐matrix composites with the PE‐g‐MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic‐particulate‐filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004     

Preparation and properties of bio‐based epoxy montomorillonite nanocomposites derived from polyglycerol polyglycidyl ether and ε‐polylysine

Glycerol polyglycidyl ether (GPE) and polyglycerol polyglycidyl ether (PGPE) were cured with ε‐poly(L ‐lysine) (PL) using epoxy/amine ratios of 1 : 1 and 2 : 1 to create bio‐based epoxy cross‐linked resins. When PGPE was used as an epoxy resin and the epoxy/amine ratio was 1 : 1, the cured neat resin showed the greatest glass transition temperature (T_g), as measured by differential scanning calorimetry. Next, the mixture of PGPE, PL, and montomorillonite (MMT) at an epoxy/amine ratio of 1 : 1 in water was dried and cured finally at 110°C to create PGPE‐PL/MMT composites. The X‐ray diffraction and transmission electron microscopy measurements revealed that the composites with MMT content 7–15 wt % were exfoliated nanocomposites and the composite with MMT content 20 wt % was an intercalated nanocomposite. The T_g and storage modulus at 50–100°C for the PGPE‐PL/MMT composites measured by DMA increased with increasing MMT content until 15 wt % and decreased at 20 wt %. The tensile strength and modulus of the PGPE‐PL/MMT composites (MMT content 15 wt %: 42 and 5300 MPa) were much greater than those of the cured PGPE‐PL resin (4 and 6 MPa). Aerobic biodegradability of the PGPE‐PL in an aqueous medium was ～ 4% after 90 days, and the PGPE‐PL/MMT nanocomposites with MMT content 7–15 wt % showed lower biodegradability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Intercalated montmorillonite by cyclotriphosphazene imidazole derivative and its thermal properties used in polyester

Montmorillonite (MMT) and hexachlorocyclotriphosphazene (HCCP) are two focal materials to investigate in improving the thermal properties of polymer in recent years. They are used to improve the thermal performance of polymer from different aspects. MMT usually could play an important role in preventing or slowing down the penetration of heat and flame by layers of the mineral. However, making polymer dehydrate and carbonize and generating incombustible ammonia, which can dilute the concentration of combustible gas, are the major ways from HCCP. In this study, a novel intercalated MMT containing high content of phosphorus and nitrogen was synthesized by MMT and HCCP (HCCP‐in‐MMT). It was applied to improve the thermal performance of polyethylene terephthalate (PET) polymer. ¹H NMR and ³¹P NMR technology were used to track the structures of a series of intermediates. The composites were prepared by melt‐blending neat PET with HCCP‐in‐MMT and named as PET/HCCP‐in‐MMT material. Three levels of HCCP‐in‐MMT (1, 3, and 5 wt%) were considered for the blends. The preliminary application in improving the thermal performance of PET was studied by thermo‐gravimetric (TG) analysis and pyrolysis–gas chromatography–mass spectrometry; pyrolysis–gas chromatography–mass spectrometry study showed that the introduction of HCCP‐in‐MMT would inhibit the pyrolysis of PET during heating or burning. The flame retardancy performance of PET composites was characterized by limiting oxygen index tests and UL‐94 test. The result showed that the composites could pass UL‐94 V‐1 and limiting oxygen index value 28.3% just only containing 5 wt% of HCCP‐in‐MMT. TEM showed that the inserted layer structure was formed between PET matrix and synthetic flame retardant HCCP‐in‐MMT. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of clay and predispersion method on the structure and properties of polystyrene (PS)‐clay nanocomposites

To prepare the polystyrene (PS)‐clay nanocomposites via an in situ emulsion polymerization, a clay predispersion method, i.e. dispersing the organic clay in the emulsifier solution by the assistance of ultrasonic, was proposed in this study. The conventional method, predispersing the organic clay into the monomer, was also presented for the comparison. The morphology analysis based on the X‐ray Deflection (XRD) and Transmission Electronic Microscopy (TEM) results suggested that the more uniform clay dispersion in the final nanocomposites could be achieved through the new method. The inorganic clay (Na‐MMT) and two organic clays (C₁₈‐MMT and VC₁₈‐MMT) synthesized by exchanging inorganic cations with the trimethyloctadecyl ammonium chloride (OTAC) and the vinylbenzyldimethyloctadecyl ammoniun chloride (VOAC) were chosen to investigate the influence of the clay surface modification on the properties of nanocomposites. The Dynamic Mechanical Analysis (DMA) results showed the storage modulus G′s of the nanocomposites had different enhancements over that of the pure PS, especially when the temperature approached the glass transition temperature (T_g). The T_gs of the nanocomposites, however, varied with the microstructure and the interactions between the polymer and the clay layers. The Na‐MMT and VC₁₈‐MMT increased the T_g, while the T_gs of PS/C₁₈‐MMT nanocomposites were slightly lower than that of the pure PS. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of organic modifiers and silicate type on filler dispersion,thermal, and mechanical properties of ABS‐clay nanocomposites

Acrylonitrile–butadiene–styrene (ABS)–clay composite and intercalated nanocomposites were prepared by melt processing, using Na‐montmorillonite (MMT), several chemically different organically modified MMT (OMMT) and Na‐laponite clays. The polymer–clay hybrids were characterized by WAXD, TEM, DSC, TGA, tensile, and impact tests. Intercalated nanocomposites are formed with organoclays, a composite is obtained with unmodified MMT, and the nanocomposite based on synthetic laponite is almost exfoliated. An unintercalated nanocomposite is formed by one of the organically modified clays, with similar overall stack dispersion as compared to the intercalated nanocomposites. T_g of ABS is unaffected by incorporation of the silicate filler in its matrix upto 4 wt % loading for different aspect ratios and organic modifications. A significant improvement in the onset of thermal decomposition (40–44°C at 4 wt % organoclay) is seen. The Young's modulus shows improvement, the elongation‐at‐break shows reduction, and the tensile strength shows improvement. Notched and unnotched impact strength of the intercalated MMT nanocomposites is lower as compared to that of ABS matrix. However, laponite and overexchanged organomontmorillonite clay lead to improvement in ductility. For the MMT clays, the Young's modulus (E) correlates with the intercalation change in organoclay interlayer separation (Δd₀₀₁) as influenced by the chemistry of the modifier. Although ABS‐laponite composites are exfoliated, the intercalated OMMT‐based nanocomposites show greater improvement in modulus. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymerizable ionic liquids for the preparation of polystyrene/clay composites

Polymerizable ionic liquids (ILs) 1‐methyl‐3‐(4‐vinylbenzyl)imidazolium chloride, 1‐hexyl‐3‐(4‐vinylbenzyl)imidazolium chloride and 1‐dodecyl‐3‐(4‐vinylbenzyl)imidazolium chloride were prepared and used as new surfactants for the modification of montmorillonite (MMT). Functionalized MMTs were prepared by cationic exchange between sodium MMT and each of the ILs. Polystyrene (PS)/MMT composites were subsequently prepared by in situ intercalative free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in the PS matrix was achieved only for MMT functionalized with the 1‐dodecyl‐3‐(4‐vinylbenzyl)imidazolium‐based IL as revealed by X‐ray diffraction and electron microscopy. The exfoliated composites showed good transparency and higher decomposition temperature than virgin polymer matrix, particularly pronounced under air atmosphere (ΔT_max = 66 °C), data comparable to or even greater than those reported in the literature for exfoliated PS nanocomposites. Copyright © 2012 Society of Chemical Industry     

Preparation,characterization, and thermal properties of polystyrene‐block‐quaternized poly(4‐vinylpyridine)/Montmorillonite nanocomposites

Polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) was synthesized by two steps of reversible addition‐fragmentation transfer (RAFT) polymerization of styrene (St) and 4‐vinylpyridine (4VP) successively. After P4VP block was quaternized with CH₃I, PS‐b‐quaternized P4VP/montmorillonite (PS‐b‐QP4VP/MMT) nanocomposites were prepared by cationic exchange reactions of quaternary ammonium ion in the PS‐b‐QP4VP with ions in MMT. The results obtained from X‐ray diffraction (XRD) and transmission electron microscopy (TEM) images demonstrate that the block copolymer/MMT nanocomposites are of intercalated and exfoliated structures, and also a small amount of silicates' layers remained in the original structure; differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results show that the nanocomposites displayed higher glass transition temperature (T_g) and higher thermal stability than that of the corresponding copolymers. The blending of PS‐b‐QP4VP/MMT with commercial PS makes MMT to be further separated, and the MMT was homogeneously dispersed in the polymer matrix. The enhancement of thermal stability of PS/PS‐b‐QP4VP/MMT is about 20°C in comparison with commercial PS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1950–1958, 2006     

Thermal stability and thermal oxidation kinetics of PU/CA-MMT composites

In this work, we prepared three composites polyurethane (PU)/chlorhexidine acetate (CA), PU/montmorillonite (MMT), and PU/CA-MMT, and investigated their kinetics of thermal degradation at different heating rates at atmosphere. These materials had good thermal stability and aging resistance. The thermal stability of PU/CA (T_onset: 237.3°C) was not obviously enhanced by the addition of only CA when compared with that of PU (T_onset: 232.3°C), while the thermal stability of PU/MMT (T_onset: 273.4°C) was considerably enhanced by the addition of MMT due to the high thermal stability of MMT. CA-MMT filler was dispersed and exfoliated in PU more easily than CA or MMT in PU, so the composite PU/CA-MMT possessed the best thermal stability (T_onset: 285.8°C). In addition, PU/CA-MMT also had the best resistance to bacterial adhesion and antibacterial ability. The analysis with Flynn-Wall-Ozawa method showed that the activation energy of thermal oxidation of PU increased when CA-MMT was added and thus its anti-aging ability was enhanced, and the thermal oxidation of these four materials was first-order reaction. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47002.