Study on the evaluation of mechanical and thermal properties of natural sisal fiber/general polymer composites reinforced with nanoclay

Composite materials, made by replacing traditional materials, are used because of their capability to produce tailor-made, desirable properties such as high tensile strength, low thermal expansion, and high strength to weight ratio. The need for the development of new materials is essential and growing day by day. The natural sisal/general polymer (GP) reinforced with nanoclay composites has become more attractive due to its high specific strength, light weight, and biodegradability. In this study, sisal–nanoclay composite is developed and its mechanical properties such as tensile strength, flexural strength, and impact strength are evaluated. The interfacial properties, internal cracks, and internal structure of the fractured surface are evaluated using scanning electron microscope. The thermal disintegration of composites are evaluated by thermogravimetric analysis. The results indicate that the incorporation of nanoclay in sisal fiber/GP can improve its properties and can be used as a substitute material for glass fiber-reinforced polymer composites.     

聚苯乙烯/聚丙烯酸丁酯乳胶互穿聚合物网络的动态力学性能研究

<正> 互穿聚合物网络(IPN)是一种新型聚合物共混物.自Sperling在1969年合成聚丙烯酸乙酯/聚苯乙烯异步IPN(Sequential IPN)后,该领域进展很快.乳胶IPN(latex IPN)是用改进的乳液聚合法合成的一种微观互穿IPN.在前文中,我们报道了聚苯乙烯/聚丙烯酸丁酯(PS/PBA)乳胶IPN的合成,本文研究一些因素对PS/PBA乳胶IPN动态力学性能的影响.     

Influence of the type of epoxy hardener on the structure and properties of interpenetrated vinyl ester/epoxy resins

The morphology–toughness relationship of vinyl ester/cycloaliphatic epoxy hybrid resins of interpenetrating network (IPN) structures was studied as a function of the epoxy hardening. The epoxy was crosslinked via polyaddition reactions (with aliphatic and cycloaliphatic diamines), cationic homopolymerization (via a boron trifluoride complex), and maleic anhydride. Maleic anhydride worked as a dual‐phase crosslinking agent by favoring the formation of a grafted IPN structure between the vinyl ester and epoxy. The type of epoxy hardener strongly affected the IPN morphology and toughness. The toughness was assessed by linear elastic fracture mechanics, which determined the fracture toughness and energy. The more compact the IPN structure was, the lower the fracture energy was of the interpenetrated vinyl ester/epoxy formulations. This resulted in the following toughness ranking: aliphatic diamine > cycloaliphatic diamine ≥ boron trifluoride complex > maleic anhydride. For IPN characterization, the width of the entangling bands and the surface roughness parameters were considered. Their values were deduced from atomic force microscopy scans taken on ion‐etched surfaces. More compact, less rough IPN‐structured resins possessed lower toughness parameters than less compact, rougher structured ones. The latter were less compatible according to dynamic mechanical thermal and thermogravimetric analyses. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5471–5481, 2004     

Synthesis and characterization of interpenetrating polymer networks with nonlinear optical properties

We report the synthesis and characterization of interpenetrating polymer networks (IPNs) exhibiting nonlinear optical (NLO) properties. The network consists of aliphatic polycarbonate urethane (PCU) and poly(methyl methacrylate-co-N,N-disubstituted urea), with a nonlinear optical (NLO) chromophore incorporated into N,N-disubstituted urea. The full IPNs have only one T_g, as determined by differential scanning calorimetry (DSC), together with scanning electron microscopy (SEM) observations, suggest a single phase morphology. The thin films of IPNs are transparent and the unpoled samples produced second harmonic generation (SHG) signals at room temperature. This result indicates that the NLO chromophore is oriented noncentrosymmetrically during the IPN formation process and is tightly held between the permanent entanglements of the two component networks of the IPN. © 1996 John Wiley & Sons, Inc.     

环氧树脂增韧改性的研究进展

概述了近年来互穿聚合物网络（IPN）、刚性粒子增韧环氧树脂的研究现状,并展望了环氧树脂增韧改性研究的前景。     

MMTCA recognition by molecular imprinting in interpenetrating polymer network hydrogels based on poly(acrylic acid) and poly(vinyl alcohol)

A novel IPN hydrogel designed to recognize MMTCA is prepared by applying the molecular-imprinting method. The IPN is characterized by FT-IR, DSC, and SEM. Langmuir analysis shows that an equal class of adsorption is formed in the hydrogel. The adsorption equilibrium constant and the maximum adsorption capacity are evaluated, and the effect of the pH on MMTCA adsorption is discussed. The selectivity of the imprinted polymer for MMTCA is studied in aqueous solutions of MMTCA/aspirin/riboflavin. The results suggest that the MMTCA-imprinted polymer shows superior selectivity for MMTCA as compared to riboflavin and aspirin. The reproducibility of the imprinted polymer to MMTCA is also studied.     

A study of the combustion and fire-retardance behaviour of unsaturated polyester/phenolic resin blends

The thermal degradation and combustion behaviour of an interpenetrating network (IPN) structure of unsaturated polyester UP resin and a resole type of phenolic resin was studied. Thermal gravimetric analysis (TGA) was used to monitor the degree of thermal decomposition for the UP/phenol IPN structure and the change of the oxygen index (OI) was used to describe the variation of the combustion behaviour. The smoke density was measured via a non-flaming process to detect the amount of smoke generated during the combustion. A homemade cone calorimetric dynamic flammability evaluation system was assembled to analyse the gas evolved and to measure the heat release rate (HRR) during the combustion. Under simulated conditions of a burning field at the temperature of 757°C, the variation of the concentration of carbon monoxide (CO) and the HRR of the UP/phenol IPN structure were studied. The results show that modification of the essentially flammable UP resin by the phenol structure to form an IPN system cannot only remarkably improve the heat resistance but also help to suppress the smoke, toxic gas and heat release during the combustion.     

Reactive compatibilization in phase separated interpenetrating polymer networks

The effects of compatibilizing additives (monomethacrylic ester of ethylene glycol (MEG) and oligo-urethane-dimethacrylate (OUDM)) on the kinetics of interpenetrating polymer network (IPN) formation based on cross-linked polyurethane and linear polystyrene and its influence on the microphase separation, viscoelastic and thermophysical properties have been investigated. It was established, that various amounts (3-10 mass%) of the additive MEG and 20 mass% OUDM introduced into the initial reaction system prevent microphase separation in the IPN. In the course of the reaction the system undergoes no phase separation up to the end of reaction, as follows from the light scattering data. The viscoelastic properties of modified IPN are changed in such a way that instead of two relaxation maxima characteristic of phase-separated system, only one relaxation maximum is observed, what is result of the formation of compatible IPN system. The position of this relaxation transition depends on the system composition and on the reaction conditions.     

高分子阻尼涂料的研究进展

介绍了高分子阻尼涂料的阻尼机理和组成,以及阻尼涂料的高分子改性方法,包括共聚、共混和互穿网络(IPN)等以及国内外发展现状。重点介绍了目前通用的树脂基料和填料,详细介绍了互穿网络改性方法和乳液聚合物互穿网络,以及环境友好水性阻尼涂料的研究现状和发展。     

Optically clear simulataneous interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and epoxy. II. Kinetic study

Simultaneous interpenetrating polymer networks (SINs) based on diglycidyl ether of bis-phenol A (DGEBA) and poly(ethylene glycol) diacrylate (PEGDA) in weight ratios of 100/0, 50/50, and 0/100 were blended and cured simultaneously by using benzoyl peroxide (BPO) and m-xylenediamine (MXDA) as curing agents. A kinetic study during SIN formation was carried out at 45, 55, 63, and 70°C. Concentration changes for both the epoxide and C?C bond were monitored with FTIR. A rate expression for DGEBA cure kinetics was established with a model reaction of phenyl glycidyl ether (PGE) and benzylamine. Experimental results revealed that lower rate constants and higher activation energy for the SIN were found, compared with those for the constituent DGEBA and PEGDA network formation. A model of network interlock was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PEGDA, the interlock (mutual entanglement) between DGEBA and PEGDA networks provided a sterically hindered environment, which subsequently increased the activation energy and reduced cure rates for both DGEBA and PEGDA. © 1993 John Wiley & Sons, Inc.     

Thermal transitions of benzene in copolymers and interpenetrating polymer networks based on hydrophilic and hydrophobic components: Experimental evidence of hydrophobic interaction

Thermal transitions of benzene in a hydrophobic polymer network have been explained by us in terms of the phase diagram of the polymer‐solvent system. In this work, we executed a similar study on copolymers and interpenetrating polymer networks (IPNs) with controllable hydrophilic/hydrophobic ratios. Copolymers and IPNs were swollen with different amounts of benzene and subjected to cooling and heating scans with differential scanning calorimetry (DSC). Synthesis of the IPNs was carried out in such a way that phase separation appeared, and three qualitatively different types of DSC thermograms were identified depending on the benzene content of IPN. Thermal transitions of benzene in the hydrophilic/hydrophobic copolymers can also be explained as a consequence of the phase diagram of the system, but an increase in the glass‐transition temperature of the system can be correlated with the interactions among the hydrophilic groups of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1713–1721, 2003     

Differential scanning calorimetric study on the curing behavior of epoxy resin/diethylenetriamine/organic montmorillonite nanocomposite

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A with diethylenetriamine as the curing agent and different amounts of organic montmorillonite were examined with isothermal and dynamic scanning calorimetry. The modified Avrami equation was used to calculate the activation energy and reaction orders in the isothermal experiment. A single peak was observed in each dynamic scan. The curing mechanism and kinetics of the curing reaction were also analyzed by two kinds of methods—Kissinger and Flynn–Wall–Ozawa. The results obtained from those methods under dynamic measurement agreed with those obtained from the modified Avrami equation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 378–386, 2003     

Heterogeneity of glass transition dynamics in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks

The peculiarities of segmental dynamics over the temperature range of ?140 to 180 °C were studied in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks (PU‐PHEMA semi‐IPNs) with two‐phase, nanoheterogeneous structure. The networks were synthesized by the sequential method when the PU network was obtained from poly(oxypropylene glycol) (PPG) and adduct of trimethylolpropane (TMP) and toluylene diisocyanate (TDI), and then swollen with 2‐hydroxyethyl methacrylate monomer with its subsequent photopolymerization. PHEMA content in the semi‐IPNs varied from 10 to 57 wt %. Laser‐interferometric creep rate spectroscopy (CRS), supplemented with differential scanning calorimetry (DSC), was used for discrete dynamic analysis of these IPNs. The effects of anomalous, large broadening of the PHEMA glass transition to higher temperatures in comparison with that of neat PHEMA, despite much lower T_g of the PU constituent, and the pronounced heterogeneity of glass transition dynamics were found in these networks. Up to 3 or 4 overlapping creep rate peaks, characterizing different segmental dynamics modes, have been registered within both PU and PHEMA glass transitions in these semi‐IPNs. On the whole, the united semi‐IPN glass transition ranged virtually from ?60 to 160 °C. As proved by IR spectra, some hybridization of the semi‐IPN constituents took place, and therefore the effects observed could be properly interpreted in the framework of the notion of “constrained dynamics.” The peculiar segmental dynamics in the semi‐IPNs studied may help in developing advanced biomedical, damping, and membrane materials based thereon. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 963–975, 2007     

Effect of new hyperbranched polyester of varying generations on toughening of epoxy resin through interpenetrating polymer networks using urethane linkages

In this study, a previously unreported methodology is attempted to improve the inherent brittleness in diglycidyl ether of bisphenol-A based epoxy resin using hyperbranched polymers as toughening agents. Four different hyperbranched polyesters (HBPs) with increasing generations (1–4, denoted as HBP-G1 to HBP-G4) were synthesized by reacting calculated amount of dipentaerythritol (used as a core) and dimethylol propionic acid (AB₂ type monomer) through pseudo one-step melt polycondensation method. The newly synthesized HBPs were characterized using spectral, thermal and physical measurements, which confirmed the formation of highly branched structure and decreasing thermal stability with increasing HBP generations. Further, toughening of the epoxy resin is carried out by reacting each generation of the HBP with epoxy using hexamethylene diisocyanate as an intermediate linkage resulting in the formation of HBP-Polyurethane/Epoxy-g-Interpenetrating Polymer Networks (HBP-PU/EP-g-IPNs). A linear polyol-PU/EP-g-IPN is also synthesized for the purpose of comparison. It is found that the HBP modified epoxy samples exhibited higher toughness in comparison to that of neat epoxy and linear polyol based epoxy samples. On the other hand, flexural properties, thermal stability and glass transition temperature of the modified samples is lower than neat epoxy sample due to the existence of flexible urethane linkages and decrease in the cross-linking density of epoxy matrix. The toughening characteristics exhibited by the HBPs are corroborated from the existence of heterogeneous morphology using SEM data.     

纳米孔阵列阳极氧化铝膜的制备和表征

本文通过在0℃、0.5mol·L^-1的草酸溶液中阳极氧化高纯铝片的方法制得了阳极氧化铝(AAO)膜，并用扫描电子显微镜(SEM)和原子力显微镜(AFM)对AAO膜的形貌和结构进行了表征。结果表明，阻挡层AAO膜中大小一致的膜胞在铝/氧化铝界面上排成六方形阵列;有孔层AAO膜中含有高度有序的纳米孔阵列和膜胞阵列，并且孔的直径和膜胞的尺寸都具有较窄的分布。另外，考察了阳极氧化电压对膜胞尺寸、孔径大小、孔密度和膜胞密度的影响，表明在一定的电压范围内，膜胞和孔径都随电压的升高而增大，而孔密度和膜胞密度却随电压的升高而减小。     

Stable second‐order NLO semi‐IPN system based on bipyridine‐containing polyimide and alkoxysilane dye

An organosoluble polyimide based on bipyridyl moiety and an alkoxysilane dye have been developed for second‐order non‐linear optics (NLOs). This bipyridine‐containing polyimide exhibits a glass transition temperature of 254°C and a degradation temperature of 400°C. An NLO‐active semi‐interpenetrating network (IPN) system was prepared by blending the polyimide with the alkoxysilane dye via in situ sol‐gel process of alkoxysilane. The selection of this bipyridine‐containing polyimide as the polymeric matrices provides improved solubility and thermal stability, and most importantly enhanced intermolecular interactions. No aggregation of the NLO chromophores in the polyimide matrices was observed through morphology and NLO studies. Under the limitation of chromophore degradation at elevated temperatures, the pristine poled/cured alkoxysilane dye exhibits poorer long‐term stability. By introducing the polyimide upon a silica network by the semi‐IPN system, randomization of the oriented chromophores can be effectively suppressed. Using in situ contact poling, the r₃₃ coefficients of 2.2–17.0 pm/V were obtained for the optically clear semi‐IPN NLO materials. Excellent temporal stability (100°C) was also achieved for these semi‐IPN materials. Copyright © 2005 John Wiley & Sons, Ltd.     

The electron microanalyzer (EPMA): a powerful device for the microanalysis of filled polymeric materials

The electron probe microanalyzer is a device often used in the field of geology or in the glass and steel industries. However, it is barely known or used in the polymer field. Thus, in this paper, we investigate the use of electron probe microanalyzer for polymer microanalyses and compared it with a scanning electron microscope equipped with an energy dispersive spectrometer. To show the unique potential of this technique only develop in our lab for polymer application, three different samples were studied: (i) a fire protective epoxy‐based coating submitted to aging in salt water, (ii) the distribution of organometallic catalysts into a thermal isolative silicone polymer, and (iii) the fouling growth of milk protein (biopolymer) on a stainless steel surface. Compared to an energy dispersive spectrometer, with an electron probe microanalyzer it is possible to quickly create X‐ray mappings of low concentration elements at a good resolution, as well as allowing the interpretation of the mechanism of action for the three samples which was impossible using only an energy dispersive spectrometer because of its too low detection resolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Ion-imprinted interpenetrating network gels for solid-phase extraction of heavy metal ions

In the present work, ion-imprinted interpenetrating polymer network (IPN) gels were prepared by free radical/cationic hybrid polymerisation of acrylamide (AAm) and 1,4-butanediol vinyl ether (BVE). These gels were respectively used for separation of Cu²⁺, Ni²⁺ and Zn²⁺ ions in natural water samples. Experimental conditions for effective adsorption of metal ions were optimised with respect to different experimental parameters by column procedures in detail. The optimum pH value for the adsorption of Cu²⁺, Ni²⁺ and Zn²⁺ ions on these sorbents was 6.0. Complete elution of the adsorbed metal ions from the sorbent was carried out using 1.0 mol/L of HCl solution. The optimum sample flow rate and eluent flow rate were, respectively, 1.0 and 0.3 mL/min. Common coexisting ions did not interfere with the separation and determination of the target ions. The accuracy of the proposed method was validated by analysis of the standard reference material (GBW 08301, river sediment). The measured contents of metal ions in the reference material were in good agreement with the certified values. The presented method was successfully applied for the determination of Cu²⁺, Ni²⁺ and Zn²⁺ ions in three different water samples (well water, seawater and waste water).     

Toughness Behaviour of Vinylester/Epoxy Thermosets with Interpenetrating Network Structure

Vinylester/epoxy-based (VE/EP) thermosets of interpenetrating network (IPN) structure were produced by using a VE resin (bismethacryloxy derivative of a bisphenol-A type EP resin) and EP resins of aliphatic (Al-EP) and cycloaliphatic (Cal-EP) nature. Curing of the EP resins occurred either by an aliphatic (Al-Am) or a cycloaliphatic (Cal-Am) diamine compound. Dynamic mechanical thermal analysis (DMTA) and atomic force microscopy (AFM) suggested the presence of an interpenetrating network (IPN) in the resulting thermosets. AFM scans taken on the ion-etched surface of EP showed a featureless homogeneous structure. On the other hand, VE exhibited a two-phase microgel, whereas VE/EP a two-phase interpenetrating network (IPN) structure. Toughness was characterised by parameters of the linear elastic fracture mechanics, viz. fracture toughness (K_c) and fracture energy (G_c). Unexpected high K_c and G_c data were found for the systems containing cyclohexylene units in the EP network. This was attributed to beneficial effects of the conformational changes along the cyclohexylene linkages (chair/boat). The failure mode of the VE/EP thermoset combinations was studied by scanning electron microscopy (SEM) and discussed.