Iranian polymer journal
Volume:21 Issue: 1, 2012

In this study, chemical modification of bamboo powder (BP)/hydroxyl-terminated polyurethane (HPU) composites obtained by hot press was investigated using blocked polyisocyanate synthesized from reaction of isophorone diisocyanate with 1,1,1-trimethylolpropane (TMP) followed by addition of methyl ethyl ketoxime (MEKO). The modified surface of MEKO-blocked polyisocyanate (M-bp)-treated BP/HPU composites was identified by Fourier transform infrared spectroscopy from the appearance of CO bands absorbance and the reduction in relative intensity of OH, with respect to bamboo. The effects of M-bp as a cross-linker on the properties of the products were studied. Mechanical testing results showed that the tensile and flexural properties of the composites were improved by addition of such a cross-linker. The morphology analysis revealed that the M-bp-modified composites exhibited better compatibility and homogeneous morphologies in comparison with the unmodified composites. Moreover, the thermogravimetric analysis demonstrated that thermal resistance of the composites was enhanced by addition of M-bp. The moisture absorption characteristics of the products were also studied and discussed, because it is a major influencing factor for natural fibre composites. The results showed that better water resistance of modified composites was obtained due to stronger interfacial adhesion. Based on the findings in this work, they all indicated that the chemical modification occurred by the cross-linking effect of M-bp, which induced the strong bonds among the composite components.

Continuous exposure to high-energy ultrasonic waves depolymerizes macromolecules in solutions and produces a permanent reduction in viscosity. Different factors affect the efficiency of this process. In this study, ultrasonic degradation of one commercially important hydrogel based on acrylic acid and acrylamide cross-linked with N,N-methylenebisacrylamide (NMBA) was carried out in aqueous solution at room temperature (25 °C). The purpose of this study was to present new experimental data for this ultrasonic degradation. In this respect, the effect of sonication parameters (power and pulse) on the rate of degradation was investigated. Granule disintegration was determined using a method to measure the swelling power of hydrogel. A method of viscometry was used to study the degradation behavior of the hydrogel and a first-order kinetic equation was employed to calculate the degradation rate constants. The experimental results indicated that the rate of ultrasonic degradation increased with increasing ultrasonic power and pulse. FTIR and UV spectrometry measurements confirmed that the degradation proceeded by mechanical forces. A detailed degradation mechanism has been proposed including chain scission. The present study has enabled us to understand the role of the ultrasonic parameters in deciding the extent of viscosity reduction in hydrogel systems.

Poly(p-methylstyrene) (Pp-MS) was synthesized at three different temperatures of 50, 150 and 250 °C via bulk thermal polymerization method. The assignment of all stereosequences at triad and pentad levels for two quaternary aromatic carbons and hexad level for methylene carbon was carried out by 13C liquid nuclear magnetic resonance spectroscopy (NMR) in deuterated chloroform at similar conditions. The probability of meso addition (P m) was calculated from second quaternary aromatic carbon and used to predict the relative intensities of methylene and first quaternary aromatic carbon by Bernoullian and first-order Markov statistical models. The results were compared with experimental data. It is shown that the Bernoullian statistics fit better than first-order Markov model for all three samples. The results indicate that P m increases by increasing polymerization temperature. The corresponding P m values determined for synthesized Pp-MSs at 50, 150 and 250 °C were 0.383, 0.392 and 0.404, respectively. It was observed that higher resolutions and better splitting patterns were achievable by increasing the NMR acquisition temperature from 20 to 50 °C. When temperature increased during NMR acquisition, the resolution improved for the first and second quaternary aromatic carbons and methylene carbon, though there was no splitting pattern observed for methyl carbon atom at the para-position of the aromatic ring.

PFSA-TiO2(or Al2O3)-PVA/PVA/PAN difunctional hollow fiber composite membranes with separation performance and catalytic activity have been prepared by dip-coating method. The good separation performance was brought about by the glutaraldehyde (GA) surface cross-linked PVA/PAN composite membrane, and the good catalytic activity of the membrane was achieved by the perfluorosulphonic acid (PFSA) used. The difunctional hollow fiber membranes were characterized by XRD, TGA, EDX, SEM, and FTIR. The separation performance was measured by dehydration of azeotropic top product of ethanol-acetic acid esterification, and the catalytic activity was obtained by investigating the esterification of ethanol and acetic acid. The FTIR spectra and the morphologies of difunctional hollow fiber composite membranes were similar for samples prior to esterification and post-esterification with ethanol and acetic acid for 24 h. Difunctional hollow fiber composite membranes with 2% PFSA, 8% TiO2 (named as DM-T1), and 2% PFSA, 8% Al2O3 (named as DM-A1) (all by weights) showed the best catalytic activity. They displayed fluxes of 165 and 173 g/m2 h, separation factors of water to ethanol of 279 and 161, PFSA contents in difunctional hollow fiber composite membrane of 3.2 and 2.4%, the ratios of PFSA to feed solution (acetic acid–ethanol) of 0.031 and 0.023%, and the equilibrium conversion of ethanol at 53.5 and 57.6%, in the given order for TiO2 and Al2O3 containing samples.

Bamboo is considered to be an important biopolymer with useful applications in various fields including textiles. It is a renewable natural resource of cellulosic nature and it originates from grass family. It gives maximum biomass per unit area and time. In general, cellulosic fibres do not have acid dyeability as those of polyamide fibres. Hence, it is difficult to dye such fibres, unless modified, with acid dyes which are relatively cheaper than the direct class of dyes. In the current study, the bamboo rayon fabric was grafted with acrylamide using potassium persulphate (KPS) as an initiator. The grafting conditions were optimized in terms of temperature, time, initiator and monomer concentrations. The grafted product was characterized using FTIR, TGA, SEM and analyzed for textile properties like moisture regain and yellowness index. The ungrafted and grafted fabrics were dyed using acid dyes and tested for colour strength and fastness properties. An increase in the dyeability of the order of 150–230% was observed on grafting of bamboo rayon. The distinct improvement in moisture regain of the grafted fabrics was also observed, which is due to increase in the polarity of the fibres. Hence, better comfort can be expected out of such fabrics during summer. The bamboo rayon which is otherwise not dyeable with acid dyes, can be rendered acid dyeable by grafting technique.

ZnO nanoparticle was used for preparing supported catalyst, which was applied in copolymerization of ethylene and 1-octene to obtain LLDPE/ZnO nanocomposite. There were two different impregnation methods (in situ and ex situ) in preparing the nano-ZnO supported catalyst. The investigation to compare both methods was conducted by employing various 1-octene initial concentrations in copolymerization. It was found that a heterogeneous catalytic system comprised a supported catalyst, prepared by in situ impregnation, provided higher catalytic activities and 1-octene incorporations compared to those of ex situ impregnation under similar condition perhaps due to closer similarity to a homogeneous system. For the ex situ impregnation, it was found that when zirconocene was directly impregnated onto the support, the catalytic activity decreased. This was due to zirconocene close vicinity to the supports and even deep into the support structure proved by XPS and TGA measurements. Therefore, it was more inaccessible to monomer attack and reducing the catalytic activity. The separate study on each catalytic system relating to the comonomer effect was also conducted by applying initial comonomer concentrations varied between 0 and 18 mmol. The increase in catalytic activity with increasing comonomer concentration can be considered as a positive comonomer effect, and the opposite was true for a negative comonomer effect. It was found that both positive and negative comonomer effects occurred in in situ impregnation and ex situ impregnation systems with Zn/(Al + Zr) support, whereas only positive comonomer effect was found in an ex situ impregnation system with Zn/Al support. This suggested that the comonomer effect was varied according to the nature of each system. The polymer properties, such as relative crystallinity and thermal properties were also investigated and found to alter with 1-octene concentration.

Thermoplastic elastomers based on the blends of thermoplastic polyurethane (TPU) and natural rubber were prepared by a simple blend technique. The influence of the two different types of natural rubber (i.e., unmodified natural rubber (NR) and epoxidized natural rubber (ENR)) on properties of the blends was investigated. The main aim of this study was to improve heat resistance and damping properties, and also to prepare the TPU material with low hardness by blending with various amounts of natural rubber. It was found that the TPU/ENR blends exhibited superior modulus, hardness, shear viscosity, stress relaxation behavior and heat-resistant properties compared to the blends with TPU and unmodified NR. This was attributed to higher chemical interaction between the polar functional groups of ENR and TPU by improving the interfacial adhesion. It was also found that the ENR/TPU blends exhibited finer grain morphology than the blends with unmodified NR. Furthermore, lower tension set, damping factor (Tan δ) and hardness, but higher degradation temperature, were observed in natural rubber/TPU blends compared to pure TPU. This proves the formation of TPU material with high heat resistance, low hardness and better damping properties. However, the blends with higher proportion of natural rubber exhibited lower tensile strength and elongation at break.