Polymer (v.48, #10)
Copolymerisation of 1,9-decadiene and propylene with binary and isolated metallocene systems
by Antti Tynys; Jan L. Eilertsen; Jukka V. Seppälä; Erling Rytter (pp. 2793-2805).
1,9-Decadiene/propylene copolymers were obtained with isolated metallocenes and with a binary metallocene catalyst system activated by methylaluminoxane. The metallocenes under investigation were syndiospecific diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and isospecific rac-dimethylsilylbis(4- tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). A copolymer structure, in which 1,9-decadiene linked isotactic and syndiotactic polymer chains, was obtained when copolymerisation was started with catalyst2 at 80°C followed by injection of catalyst1 and instantaneous lowering of polymerisation temperature to 40°C after 15min of polymerisation. The copolymer was also shown to work as a compatibiliser in a blend of syndiotactic and isotactic polypropylene. We propose that catalyst2 incorporates 1,9-decadiene into the isotactic main chain without any significant crosslinking within the first 15min of polymerisation at 80°C and the produced isotactic macromonomers are further incorporated at 40°C into the syndiotactic main chain in polymerisation with catalyst1.
Keywords: Copolymer; Metallocene catalyst; Polypropylene
Functionalized polystyrene latex particles as substrates for ATRP: Surface and colloidal characterization
by V. Mittal; N.B. Matsko; A. Butté; M. Morbidelli (pp. 2806-2817).
In this work, the process for producing polystyrene particles surface functionalized with a thin shell of ATRP initiator polymerized alone or along with styrene and a crosslinker, is presented. Copolymerization of styrene and acrylic end-capped ATRP initiator to generate a thin shell on the fully polymerized core particles suffered from secondary nucleation owing to their possible incompatibility with the core particles and their own colloidal stability. One step functionalization processes, where the shell forming monomers are added directly to the 70% polymerized core particles, lead to significant changes in the resulting particle morphologies. The shot addition of these monomers led to a very uniform surface morphology without any secondary nucleation owing to quick coalescence of the secondary particles on the soft surface of the seed particles. Addition of crosslinker to the system helped in effectively eliminating the smaller particles generated due to secondary nucleation along with the chemical networking.
Keywords: Polystyrene; Emulsion polymerization; Electron microscopy
Surface segregation of branched polyethyleneimines in a thermoplastic polyurethane
by Joshua A. Orlicki; Wendy E. Kosik; J. Derek Demaree; Matthew S. Bratcher; Robert E. Jensen; Steven H. McKnight (pp. 2818-2826).
Hyperbranched polyethyleneimines were modified with methacrylated fluorosurfactants and aliphatic epoxides to provide a library of macromolecules with controlled chain ends and residual amine functionality. These materials were co-dissolved with a thermoplastic polyurethane-ether and the blends were subsequently deposited as films cast from solution. The surface chemistry of the cast films was determined using angle resolved X-ray photoelectron spectroscopy (AR-XPS) and Rutherford backscattering spectroscopy (RBS). Experimental results indicate that the modified hyperbranched polymers (HBPs) concentrate at the air–polymer interface. Furthermore, HBPs that were complexed to polyoxometalates (POMs) using electrostatic interactions also exhibited surface segregation in cast polymer films, resulting in ca. 10-fold increase of metal at the film surface relative to the known bulk concentration. Results from XPS and RBS examination of the films are consistent with surface segregation of the HBP–POM hybrids, exhibiting increased metal, fluorine, and nitrogen content near the surface of the film, as well as significant changes in wetting behavior. This study indicates that modified HBPs may be used to selectively transport inorganic species such as polyoxometalates to polymer film surfaces.
Keywords: Hyperbranched polymer; Surface segregation; Polyoxometalate
In situ micro/nano-hydrogel synthesis from acrylamide derivates with lecithin organogel system
by Nurettin Sahiner; Mohit Singh (pp. 2827-2834).
Acrylamide based hydrogel particles with variable charge were synthesized in different sizes using a biocompatible surfactant. We use microemulsion polymerization to synthesize the hydrogel particles in lecithin organogel systems. The phospholipid, lecithin, is a soybean extract that exhibits a rich phase behavior depending on various factors such as amount of water, co-solvent, additives and their concentrations. By UV irradiation of water-in-oil microemulsions of lecithin, containing different monomers, phospholipid coated hydrogels were synthesized in situ. The hydrogel particle size varies from a few hundred nanometers to tens of micrometer. The response time of these micron sized hydrogel particles, as measured by swelling experiments, is very fast (∼100s) in comparison with their corresponding bulk hydrogels (∼101h). The positively charged cationic hydrogel microparticles were embedded/dispersed into another hydrogel matrix to render responsive behavior to a non-responsive matrix. Besides TEM and SEM studies, fluorescein dye absorption studies were also performed in order to visualize the hydrogel microparticles. Additionally, anionic hydrogel micro/nano-particles were also synthesized in the lecithin system.
Keywords: Micro/nano-hydrogels; Phospholipid coated hydrogels; Biomaterials
Controllable synthesis of poly( N-vinylpyrrolidone) and its block copolymers by atom transfer radical polymerization
by Xiaoju Lu; Shuling Gong; Lingzhi Meng; Cheng Li; Shu Yang; Lifen Zhang (pp. 2835-2842).
At room temperature atom transfer radical polymerization (ATRP) of N-vinylpyrrolidone (NVP) was carried out using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclo-tetradecane (Me6Cyclam) as ligand in 1,4-dioxane/isopropanol mixture. Methyl 2-chloropropionate (MCP) and copper(I) chloride were used as initiator and catalyst, respectively. The polymerization of NVP via ATRP could be mediated by the addition of CuCl2. The resultant poly( N-vinylpyrrolidone) (PNVP) has high conversion of up to 65% in 3h, a controlled molecular weight close to the theoretical values and narrow molecular weight distribution between 1.2 and 1.3. The living nature of the ATRP for NVP was confirmed by the experiments of PNVP chain extension. With PNVP–Cl as macroinitiator and N-methacryloyl- N′-(α-naphthyl)thiourea (MANTU) as a hydrophobic monomer, novel fluorescent amphiphilic copolymers poly( N-vinylpyrrolidone)- b-poly( N-methacryloyl- N′-(α-naphthyl)thiourea) (PNVP- b-PMANTU) were synthesized by ATRP. PNVP- b-PMANTU copolymers were characterized by1H NMR, GPC-MALLS and fluorescence measurements. The results revealed that PNVP- b-PMANTU presented a blocky architecture.
Keywords: Poly(; N; -vinylpyrrolidone); ATRP; Cyclic ligand
Electrochemical polymerization of water-soluble and insoluble monomers in supercritical carbon dioxide-in-water emulsion
by Mitsutoshi Jikei; Hajimu Yasuda; Hideaki Itoh (pp. 2843-2852).
Dense carbon dioxide is an environmentally benign solvent, but its non-polarity limits the use of carbon dioxide as a reaction medium for electrochemical reactions. We have previously reported that the electrochemical polymerization in a carbon dioxide-in-water (C/W) emulsion proceeds to form conductive polypyrrole films [Jikei M, Saitoh S, Yasuda H, Itoh H, Sone M, Kakimoto M, et al. Polymer 2006;47:1547–54]. In this study, the effect of reaction conditions of the electrochemical polymerization on the resulting polypyrrole films was systematically investigated in order to reveal the features, flexibility and limitations of the C/W emulsion as a medium for electrochemical reactions. Other monomers, such as aniline and 3,4-ethylenedioxythiophene, were also examined for the electrochemical polymerization in the C/W emulsion. We have found that water-soluble monomers, such as pyrrole and aniline, are suitable for the electrochemical polymerization in the C/W emulsion that form films with a fine uneven texture.
Keywords: Conductive polymers; Supercritical carbon dioxide; Electrochemical polymerization
Synthesis and characterization of ZnS/hyperbranched polyester nanocomposite and its optical properties
by Yongbin Zhao; Feng Wang; Qi Fu; Wenfang Shi (pp. 2853-2859).
The ZnS/hyperbranched polyester nanocomposite with higher refractive index was prepared by incorporating the acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped ZnS nanoparticles into the acrylated Boltorn™ H20 (H20). The acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped colloidal ZnS nanoparticles were synthesized by the reaction of zinc acetate with thioacetamide in N, N-dimethylformamide. The acrylated hyperbranched polyester was obtained by reacting acryloyl chloride with hydroxyl group of H20. The acrylated H20 plays an important role in stabilizing and dispersing ZnS nanoparticles with a diameter of 1–4nm. The refractive indices of ZnS/hyperbranched polyester nanocomposites, depending on ZnS content, were determined to be in the ranges of 1.48–1.65.
Keywords: Hyperbranched polyester; Zinc sulfide; Nanocomposite
Cyclic acetal as coinitiator for bimolecular photoinitiating systems
by Suqing Shi; Hong Gao; Gangqiang Wu; Jun Nie (pp. 2860-2865).
Cyclic acetals were used to replace the conventional amines in bimolecular photoinitiating systems. The mixtures of benzophenone derivatives and cyclic acetals were used to initiate the UV photopolymerization of 1,6-hexanedioldiacrylate (HDDA). Camphorquinone (CQ)/1,3-benzodioxole (BDO) combinations were used to initiate the visible light photopolymerization of 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) (70/30wt%) for dental application. The kinetics was recorded by real-time infrared spectroscopy (RTIR). Ethyl 4- N, N-dimethylaminobenzoate (EDMAB) was used as control in the same photocuring condition. The results showed that the addition of cyclic acetals greatly increased the rate of polymerization ( Rp) and final double bond (DC) of HDDA. Combination of p-chlorobenzophenone (CBP)/BDO had the highest initiating reactivity. BDO also showed an effective coinitiator for camphorquinone-based initiator system. Comparing with EDMAB, CBP/BDO and CQ/BDO indicated comparable initiating reactivity. Moreover, the natural component characteristics of BDO made it a promising alternative to commercial amine in biomolecular photoinitiating system.
Keywords: Bimolecular photoinitiating system; Coinitiator; Photopolymerization
Grafting polymers onto carbon black surface by trapping polymer radicals
by Qiang Yang; Li Wang; Weidong Xiang; Junfeng Zhou; Jianhua Li (pp. 2866-2873).
Polystyrene, poly(styrene- co-maleic anhydride), poly[styrene- co-(4-vinylpyridine)] and poly(4-vinylpyridine) with well-defined molecular weights and polydispersities were synthesized using 4-hydroxyl-2,2,6,6-tetramethylpiperidin-1-oxyl (HTEMPO)-mediated radical polymerization initiated by azobisisobutyronitrile or benzoyl peroxide. The resultant polymers were grafted onto carbon black surface through a radical trapping reaction at 130°C in DMF.1H NMR, TGA, TEM, AFM, DSC and dynamic light scattering were used to characterize the carbon black grafted with polymers. It was found that the carbon black grafted with polystyrene and poly(styrene- co-maleic anhydride) could be dispersed in THF, chloroform, dichloromethane, DMF, etc., and the carbon black grafted with poly(4-vinylpyridine) and poly[styrene- co-(4-vinylpyridine)] could be well dispersed in ethanol.
Keywords: HTEMPO; Radical trapping; Carbon black
Robust polymer gel opals – An easy approach by inter-sphere cross-linking gel nanoparticle assembly in acetone
by Bo Zhou; Jun Gao; Zhibing Hu (pp. 2874-2881).
Narrowly distributed poly( N-isopropylacrylamide- co-acrylic acid) (PNIPAM- co-AA) nanoparticles with different particle sizes were synthesized and used as building blocks to form crystalline polymer gels. It was found that PNIPAM- co-AA nanoparticles can self-assemble into crystalline arrays in organic solvent as indicated by their iridescent colors and by the scattering peak in UV–vis spectra caused by Bragg diffraction. These crystalline structures were stabilized in acetone using epichlorohydrin to cross-link neighboring particles at ∼90°C. The resultant opals had much higher polymer concentration than that of similar hydrogels. Due to their higher polymer contents, these opals had much better mechanical strength and could undergo the solvent exchange from an organic solvent to water without being broken. Kinetics of the solvent exchange was measured and explained in terms of the volume phase transition of the PNIPAM in mixed solvents. Shear modulus of the opal was measured in the linear stress-yield ranges for the same gel crystals in both acetone and water.
Keywords: Polymer gels; Opal; Nanoparticles
EPR/rheometric studies on radical kinetics in melt polyolefin elastomer initiated by dicumyl peroxides
by Jianye Liu; Wei Yu; Chengxue Zhao; Chixing Zhou (pp. 2882-2891).
Peroxide-initiated reaction of poly(ethylene- co-α-butene) (EB), a kind of polyolefin elastomer (POE), was studied at elevated temperatures using an on-line electron paramagnetic resonance (EPR) spectrometer and was also evaluated by monitoring the viscosity of the reaction system on a rotational rheometer. It is clear that the reaction process experiences the free radical mechanisms. According to the EPR spectra, notable changes in signal hyperfine structure, the intensity and lifetime of the radical were recognized. Different from the case of PE and PP modified by peroxide, there is a new type of EPR signal, which is assisted to the tertiary alkyl radicals. And it is verified that the primary alkyl radicals are first produced at elevated temperatures. A rheokinetic analysis was made by EPR and rheology. The kinetic coefficients of coupling and disproportionating reactions were not fixed, but the functions of the reacting time or the system viscosity. Accordingly, the kinetics is substantially controlled by diffusion of the polymer chains and a formula reflecting this kind of effect of the viscosity on termination rate coefficients is founded.
Keywords: POE; EPR; Rheokinetics
Synergic flame retardancy mechanism of montmorillonite in the nano-sized hydroxyl aluminum oxalate/LDPE/EPDM system
by Zhi-Hong Chang; Fen Guo; Jian-Feng Chen; Lei Zuo; Jiang-Hua Yu; Guo-Quan Wang (pp. 2892-2900).
Nano-sized hydroxyl aluminum oxalate (nano-HAO) and montmorillonite (MMT) were mixed into low density polyethylene (LDPE)/ethylene propylene diene rubber (EPDM) system via melt compounding method. By means of LOI and UL94 horizontal burning tests, MMT and nano-HAO together exhibited better performance on flame-retarding LDPE/EPDM composites than how they performed individually, which proved that there existed a synergistic effect between MMT and nano-HAO on flame retardancy. Furthermore, through the analysis of Fourier transform IR spectra (FTIR), scanning electron microscope (SEM), and the thermogravimetric and differential thermal analysis (TG–DTA), the mechanism of the synergistic flame retardance was proposed as when MMT was added into nano-HAO/LDPE/EPDM composites, a laminated structure formed in the char layer and thus the transmission speeds of heat, oxygen, flammable mass and vapor were adjusted. So the process of combustion was retarded owing to lack of oxygen and heat.
Keywords: Hydroxyl aluminum oxalate (HAO); Montmorillonite (MMT); Flame retardancy
Miscibility study of Torlon® polyamide-imide with Matrimid® 5218 polyimide and polybenzimidazole
by Yan Wang; Suat Hong Goh; Tai-Shung Chung (pp. 2901-2909).
We have discovered two new miscible polymer blend systems, namely, Torlon® 4000T with Matrimid® 5218 and Torlon 4000T with polybenzimidazole (PBI). Both Matrimid 5218 and PBI are miscible at a molecular level with Torlon 4000T over the whole composition range as confirmed by microscopy, DSC, FTIR and DMA. DSC and DMA studies show the existence of a single glass transition in each blend. The Tg-composition curve of Torlon/Matrimid blend system forms a sigmoid curve as a function of composition, while the Tg-composition curve of the Torlon/PBI blend system is double parabola-like. FTIR spectra show the existence of hydrogen-bonding interactions in these two polymer blend systems.
Keywords: Torlon; Miscible polymer blend; T; g; -composition curve
Surface immobilization of polymer brushes onto porous poly(vinylidene fluoride) membrane by electron beam to improve the hydrophilicity and fouling resistance
by Fu Liu; Chun-Hui Du; Bao-Ku Zhu; You-Yi Xu (pp. 2910-2918).
Poly(vinylidene fluoride) (PVDF) membrane was pre-irradiated by electron beam, and then poly(ethylene glycol) methyl ether methacrylate (PEGMA) was grafted onto the membrane surface in the aqueous solution. The degree of grafting was significantly influenced by the pH value of the reaction solution. The surface chemical changes were characterized by the Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Combining with the analysis of the nuclear magnetic resonance proton and carbon spectra (1H NMR and13C NMR), PEGMA was mainly grafted onto the membrane surface. Morphological changes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The porosity and bulk mean pore size changes were determined by a mercury porosimeter. The surface and bulk hydrophilicity were evaluated on the basis of static water contact angle, dynamic water contact angle and the dynamic adsorption process. Furthermore, relative high permeation fluxes of pure water and protein solution were obtained. All these results demonstrate that both hydrophilicity and fouling resistance of the PVDF membrane can be improved by the immobilization of hydrophilic comb-like polymer brushes on the membrane surface.
Keywords: PVDF membrane; Electron beam; Hydrophilicity
Dynamic interplay between phase separation and crystallization in a poly(ɛ-caprolactone)/poly(ethylene glycol) oligomer blend
by Wei-Tsung Chuang; U.-Ser. Jeng; Po-Da Hong; Hwo-Shuenn Sheu; Ying-Huang Lai; Kan-Shan Shih (pp. 2919-2927).
We have investigated the crystallization effect on the phase separation of a poly(ɛ-caprolactone) and poly(ethylene glycol) oligomer (PCL/PEGo) blending system using simultaneous small-angle light scattering and differential scanning calorimetry (SALS/DSC) as well as simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and DSC (SAXS/WAXS/DSC). When the PCL/PEGo system, of a weight ratio of 7/3, is quenched from a melt state (160°C) to temperatures below the spinodal point and the melting temperature of PCL (63°C), the structural evolution observed exhibits characteristics of (I) early stage of spinodal decomposition (SD), (II) transient pinning, (III) crystallization-induced depinning, and (IV) diffusion-limited crystallization. The time-dependent scattering data of SALS, SAXS and WAXS, covering a wide range of length scale, clearly show that the crystallization of PCL intervenes significantly in the ongoing viscoelastic phase separation of the system, only after the early stage of SD. The effect of preordering before crystallization revives the structural evolution pinned by the viscoelastic phase separation. The growth of SAXS intensity during the preordering period conforms to the Cahn–Hilliard theory. In the later stage of the phase separation, the PCL-rich matrix, of spherulite crystalline domains developed due to the faster crystallization kinetics, traps the isolated PEGo-rich domains of a slower viscoelastic separation.
Keywords: Crystallization; Viscoelastic phase separation; Spinodal decomposition
The domain structure and mobility of semi-crystalline poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate- co-3-hydroxyvalerate): A solid-state NMR study
by Limin Zhang; Huiru Tang; Guangjin Hou; Yiding Shen; Feng Deng (pp. 2928-2938).
Solid-state NMR techniques have been employed to investigate the domain structure and mobility of the bacterial biopolymeric metabolites such as poly(3-hydroxybutyrate) (PHB) and its copolymers poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) containing 2.7mol% (PHBV2.7) and 6.5mol% (PHBV6.5) 3-hydroxyvalerate. Both single-pulse excitation with magic-angle spinning (SPEMAS) and cross-polarization magic-angle spinning (CPMAS)13C NMR results showed that these biopolymers were composed of amorphous and crystalline regions having distinct molecular dynamics. Under magic-angle spinning,1H T1 ρ and13C T1 showed two processes for each carbon. Proton relaxation-induced spectral editing (PRISE) techniques allowed the neat separation of the13C resonances in the crystalline regions from those in the amorphous ones. The proton spin–lattice relaxation time in the tilted rotating frame,HT1ρT, measured using the Lee–Goldburg sequence with frequency modulation (LGFM) as the spin–locking scheme, was also double exponential and significantly longer than1H T1 ρ. The difference betweenHT1ρT for the amorphous and crystalline domains was greater than that of1H T1 ρ. Our results showed that theHT1ρT differences could be exploited in LGFM–CPMAS experiments to separate the signals from two distinct regions.1H spin-diffusion results showed that the domain size of the mobile components in PHB, PHBV2.7 and PHBV6.5 were about 13, 24 and 36nm whereas the ordered domain sizes were smaller than 76, 65 and 55nm, respectively. The results indicated that the introduction of 3-hydroxyvalerate into PHB led to marked molecular mobility enhancement in the biopolymers.
Keywords: Solid-state NMR; Poly(3-hydroxybutyrate); Poly(3-hydroxybutyrate-; co; -3-hydroxyvalerate)
Novel PVA–silica nanocomposite membrane for pervaporative dehydration of ethylene glycol aqueous solution
by Ruili Guo; Xiaocong Ma; Changlai Hu; Zhongyi Jiang (pp. 2939-2945).
To effectively suppress the swelling of poly(vinyl alcohol) (PVA) membrane, polymer–inorganic nanocomposite membranes composed of PVA and γ-mercaptopropyltrimethoxysilane (MPTMS) were prepared by in situ sol–gel technique for pervaporative separation of water–ethylene glycol (EG) mixtures. Effects of the types of catalyst for sol–gel process and MPTMS content on the physical and chemical structure of PVA–silica nanocomposite membranes (designated as PVA–MPTMS hereafter) were investigated by29Si NMR, FTIR, SEM, XRD and TGA–DTA. Due to the formation of more compact crosslinked structure, nanocomposite membranes exhibited enhanced thermal stability. It was found that when 50wt% of MPTMS was incorporated into PVA, the nanocomposite membranes possessed optimum pervaporation performance for 80wt% EG aqueous solution at 70°C. Unexpectedly, there was no improvement in the pervaporation performance of PVA–MPTMS nanocomposite membranes after mercapto group was oxidized into sulfonic group.
Keywords: Poly(vinyl alcohol)–silica; Nanocomposite membranes; Pervaporation dehydration
Morphology and thermal properties in the binary blends of poly(propylene- co-ethylene) copolymer and isotactic polypropylene with polyethylene
by Jean-Hong Chen; Jin-Cai Zhong; Yi-Hang Cai; Wen-Bin Su; Yao-Bin Yang (pp. 2946-2957).
The morphology and thermal properties of isothermal crystallized binary blends of poly(propylene- co-ethylene) copolymer (PP- co-PE) and isotactic polypropylene (iPP) with low molecular weight polyethylene (PE) were studied with differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). In PP- co-PE/PE binary blends, however, the connected PE acted as a phase separating agent to promote phase separation for PP- co-PE/PE binary blends during crystallization. Therefore, the thermal properties of PP- co-PE/PE presented double melting peaks of PE and a single melting temperature of PP during melting trace; on the other hand, at cooling trace, the connected PE promoted crystallization rate because of enhanced segmental mobility of PP- co-PE during crystallization. At isothermal crystallization temperature between the melting points of iPP and PE, the binary blend was a crystalline/amorphous system resulting in persistent remarkable molten PE separated domains in the broken iPP spherulite. And then, when temperature was quenched to room temperature, the melted PE separated domains were crystallized that presented a crystalline/crystalline system and formed the intra-spherulite segregation morphology: these PE separated domains/droplet crystals contained mixed diluent PE with connected PE components. On the other hand, in the iPP/PE binary blends, the thermal properties showed only single melting peaks for both PE and iPP. Moreover, the glass transition temperature of iPP shifted to lower temperature with increasing PE content, implying that the diluent PE molecules were miscible with iPP to form two interfibrillar segregation morphologies: iPP-rich and PE-rich spherulites. In this work, therefore, we considered that the connected PE in PP- co-PE functioned as an effective phase separating agent for PP and diluent PE may be due to the miscibility between connected PE and diluent PE larger than that between PP and dispersed PE.
Keywords: PP-; co; -PE/PE and iPP/PE binary blends; Miscibility; Thermal properties
Effect of temperature and strain rate on the tensile deformation of polyamide 6
by Gui-Fang Shan; Wei Yang; Ming-bo Yang; Bang-hu Xie; Jian-min Feng; Qiang Fu (pp. 2958-2968).
The effects of the draw temperature and the strain rate on the tensile deformation of polyamide 6 (PA6) were investigated using three PA6 samples with different initial shapes and physical dimensions. It is observed that the special double yielding phenomenon is indeed present in PA6, provided that certain temperature and strain rate are given, as well as the appropriate initial structure. The results also show that the dependence of the first yield stress on temperature is nearly linear while on strain-rate is logarithmic. The temperature and strain-rate sensitivity change at the draw temperature in the vicinity of the glass transition temperature of PA6. The double yielding of PA6 is not only the combination of two thermally activated rate processes depending on temperature and strain rate, but also associated with the initial structure of samples. The yielding manner for PA6 seems to be determined by the synergetic effect of both the deformation of amorphous and crystalline phases. Thus some special structure involving the crystalline and amorphous phases should come into being in PA6 exhibiting double yielding. Especially the important role of inter- and intra-link should be taken into account. The theory of partial melting–recrystallization cannot account fully for the double yielding of PA6.
Keywords: Draw temperature; Strain rate; Double yield
High improvement in the properties of exfoliated PU/clay nanocomposites by the alternative swelling process
by Y.W. Chen-Yang; Y.K. Lee; Y.T. Chen; J.C. Wu (pp. 2969-2979).
In this work, a stable de-aggregated solvent-swollen organic modified clay, ALA–MMT, suspension is prepared by an efficient solvent swelling process using a home-made shaking mixer. It is found that the estimated average size of the as-prepared organoclay particles in the suspension is reduced to about 155nm, which has not been reported before. The X-ray diffraction (XRD) patterns confirm that the d-spacing of the silicate layers of the solvent-swollen ALA–MMT expands from 1.4nm to about 2.1nm. The de-aggregated solvent-swollen ALA–MMT suspension is then used with polyurethane (PU) to prepare a series of highly exfoliated and high-organoclay-loading nanocomposites, PU/ALA–MMT. Both the XRD patterns and the TEM photographs of the as-prepared PU/ALA–MMT nanocomposites indicate that the organoclay is uniformly dispersed in the PU matrix with a highly exfoliated morphology structure of up to 7wt% loading. Meanwhile, the TEM photographs give the first report for PU/clay nanocomposites which are almost completely exfoliated, and ∼1-nm thin silicate nanolayers are homogeneously dispersed in the polymer matrix with a high aspect ratio of 30–100. The thermal, mechanical, and anti-corrosion properties are all tremendously enhanced for the as-prepared nanocomposites. The results obtained for the PU nanocomposite with 7wt% ALA–MMT loading (PUC7) reveal a 19°C increment in Tg, a 48°C increment in T5%, a 248% increase in the tensile strength, and a 123% increase in the elongation. The stainless steel disk (SSD) coated with PUC7 shows the lowest corrosion rate of 2.01×10−6mm/year, which is 469% lower than that of the SSD coated with pure PU. The reinforcements are much greater than the previously reported PU/clay nanocomposites with comparable clay loadings ascribed to the exceptional homogeneity of as-prepared nanocomposites, which are accredited largely to the stable de-aggregated solvent-swollen organoclay suspension generated by the efficient solvent swelling process.
Keywords: Polyurethane; Clay; Nanocomposite
Spherulite morphology and crystallization behavior of poly(trimethylene terephthalate)/poly(ether imide) blends
by Jong Kwan Lee; Mi Ju Choi; Jeong Eun Im; Dong Jun Hwang; Kwang Hee Lee (pp. 2980-2987).
The spherulite morphology and crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). Thermal analysis showed that PTT and PEI were miscible in the melt over the entire composition range. The addition of PEI depressed the overall crystallization rate of PTT and affected the texture of spherulites but did not alter the mechanism of crystal growth. When a 50/50 blend was melt-crystallized at 180°C, the highly birefringent spherulite appeared at the early stage of crystallization ( t<20min). After longer times, the spherulite of a second form was developed, which exhibited lower birefringence. The SALS results suggested that the observed birefringence change along the radial direction of the spherulite was mainly due to an increase in the orientation fluctuation of the growing crystals as the radius of spherulite increased. The lamellar morphological parameters were evaluated by a one-dimensional correlation function analysis. The amorphous layer thickness showed little dependence on the PEI concentration, indicating that the noncrystallizable PEI component resided primarily in the interfibrillar regions of the growing spherulites.
Keywords: Spherulite morphology; Crystallization behavior; PTT
Modeling of vapor sorption in glassy polymers using a new dual mode sorption model based on multilayer sorption theory
by Haidong Feng (pp. 2988-3002).
Conventional dual mode sorption (CDMS) model is one of the most effective models in describing vapor sorption isotherms with a concave towards the activity axis in glassy polymers, while engaged species induced clustering (ENSIC) model has been approved to be highly successful in modeling vapor sorption isotherms in polymers with a convex to the activity axis (BET type III) over a wide range. However, neither of them is effective to describe other types of vapor sorption isotherms, especially sigmoidal isotherms. The Guggenheim–Anderson–de Boer (GAB) model fits extremely well with sigmoidal isotherms such as some vapor especially water vapor sorption data in food and related natural materials. However, one assumption of the GAB model for vapor sorption in glassy polymers is inconsistent with the fact that there are two species of sorption sites as the CDMS model assumes. Based on multilayer sorption theory on which the Guggenheim–Anderson–de Boer (GAB) model is based, a new dual mode sorption (DMS) model for vapor sorption in the glassy polymers is deduced. The mathematical meanings and the physicochemical significances of the parameters in the new model are analyzed. The new model has been verified experimentally by some special cases. Comparisons of the new DMS model with the CDMS and the ENSIC models prove that only the new model fits extremely well with all types of vapor sorption isotherms in the glassy polymers.
Keywords: Glassy polymer; Vapor sorption; GAB model
Cyclic viscoplasticity of solid polymers: The effects of strain rate and amplitude of deformation
by A.D. Drozdov; J.deC. Christiansen (pp. 3003-3012).
Observations are reported on polypropylene random copolymer in uniaxial cyclic tensile tests with various strain rates (ranging from 1.7×10−4 to 8.3×10−3s−1). Each cycle of deformation involves tension up to the maximal strain εmax (from 0.05 to 0.20) and retraction down to the zero stress. The study focuses on deformation programs with 10–50 cycles in each test. A constitutive model is derived for the viscoplastic behavior of a solid polymer at three-dimensional cyclic deformations with small strains. Material constants in the stress–strain relations are found by fitting the experimental data. Good agreement is demonstrated between the observations and the results of numerical simulation.
Keywords: Polypropylene; Viscoplasticity; Cyclic deformation
A steered molecular dynamics study on peptide sequence prediction from force-extension profiles
by Linxi Zhang; Tingting Sun; Jun Cheng; Haizhu Ma (pp. 3013-3020).
A study of the peptide sequence prediction based on the steered molecular dynamics (SMD) method is presented. Here, 2 22-residue peptide sequences are selected. One is the neutral sequence and the other is the LNB sequence. Force-extension profiles are easily obtained from the steered molecular dynamics simulation. For the N22 sequence, it is shown that the force curve is of saw-tooth pattern. There are 22 peaks in the curves, and each peak in the curve denotes one residue in the sequence. For the LNB sequence, 3 force curves corresponding to the desorption from 3 different attractive surfaces are shown. The residues L (hydrophilic), N (neutral), and B (hydrophobic) in the sequence can be read easily from the peaks of the curves. End-to-end distance R2 is also discussed for the 2-peptide sequences. Finally, we calculate adsorbed energy curves during the desorption process, and there are some steps in the curves, which are like the peaks in the force profiles. That is, from those steps in the energy curves, the residue prediction for the peptide sequence can also be done accurately.
Keywords: Steered molecular dynamics (SMD); LNB; sequence; Force-extension profiles