The dynamic mechanical properties such as storage modulus, loss modulus and damping properties of blends of nylon copolymer (PA6,66) with ethylene propylene diene (EPDM) rubber was investigated with special reference to the effect of blend ratio and compatibilisation over a temperature range –100°C to 150°C at different frequencies. The effect of change in the composition of the polymer blends on tanδ was studied to understand the extent of polymer miscibility and damping characteristics. The loss tangent curve of the blends exhibited two transition peaks, corresponding to the glass transition temperature (Tg) of individual components indicating incompatibility of the blend systems. The morphology of the blends has been examined by using scanning electron microscopy. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends. Finally, attempts have been made to compare the experimental data with theoretical models.
The adhesion properties, i. e. viscosity, tack and peel strength of styrene-butadiene rubber (SBR)/Standard Malaysian Rubber (SMR L)-based pressure-sensitive adhesive was studied using phenol formaldehyde resin as the tackifying resin. Toluene was used as the solvent throughout the experiment. SBR composition in SBR/SMR L blend used was 0, 20, 40, 60, 80, 100%. Three different resin loadings, i. e. 40, 80 and 120 parts per hundred parts of rubber (phr) were used in the adhesive formulation. The viscosity of adhesive was determined by a HAAKE Rotary Viscometer whereas loop tack and peel strength of paper/polyethylene terephthalate (PET) film were measured using a Lloyd Adhesion Tester operating at 30 cm/min. Results indicate that the viscosity of adhesive decreases with increasing % SBR whereas loop tack passes through a maximum value at 20% SBR for all resin loadings. Except for the control sample (without resin), the peel strength shows a maximum value at 60% SBR for the three modes of peel tests. For a fixed % SBR, adhesive sample containing 40 phr phenol formaldehyde resin always exhibits the highest loop tack and peel strength, an observation which is associated to the optimum wettability of adhesive on the substrate.
The technique of gently harvesting cells and cell sheets using stimuli-responsive cell culture carriers was applied to human umbilical vein cord endothelial cells (HUVEC). To meet the particular requirements of this demanding cell type, a copolymer consisting of N-isopropylacrylamide and diethyleneglycol methacrylate (poly(NiPAAm-co-DEGMA)) was combined with a fine-tuned protein pre-coating. Using this approach the detachment of HUVEC sheets was studied. Furthermore, the behavior of the extracellular matrix upon cell detachment was followed by protein staining. The results demonstrate the feasibility of harvesting HUVEC sheets from stimuli-responsive polymer layers and provide valuable options for the advanced engineering of vascular structures.
To investigate the influence of carbon fiber (CF) surface treatment on the flexural strength and tribological properties of the short-cut CF/polyimide (PI) composites, pitch-based short-cut CF were treated by rare earth. The CF before and after treatment was examined by X-ray photoelectron spectroscopy (XPS) and by scanning electron microscopy (SEM). The flexural strength of the specimens was determined in a three-point test machine. The friction and wear behaviors of PI composites sliding against GCr15 steel rings were evaluated on an M-2000 model ring-on-block test rig. The results show that the surface of the treated CF became rougher and there formed lots of active groups after rare earth treatment. The flexural strength of PI composites with rare earth treated CF was improved. The friction coefficient and wear rate of PI composites with rare earth treated CF were lower than that with untreated CF.
Thanks to the differential photocalorimetry technique DPC, characteristics of negative photoresists (Riston® PM 215 and Riston® MM 140, 1 mil or 25.4 µm thickness) to be developed in nonorganic aqueous medium) used in microlithography are highlighted. The photoreactivity (being evaluated by DPC) of the matrix polymer involved in these Riston® is critical for ensuring good lithographic performance. The influence of temperature and irradiation intensity on kinetic parameters such as the enthalpy of reaction ΔH, the time of induction (It), the conversion rate to the maximum peak (RPM), the coefficient rate of the reaction (k), the conversion rate α, and the polymerization rate Rp were studied. All the results highlights not only the strong differences between the two Riston® studied, but also the great reactivity of Riston® PM 215 compared to Riston® MM 140.
Alkali-treated sisal fibres were used as novel reinforcement to obtain composites with self-synthesized ureaformaldehyde resin as matrix phase. The composites were prepared by means of compression molding, and then the effects of sisal loading on mechanical properties such as impact strength, flexural strength, and wear resistance were investigated. In addition, water uptake was studied and structural features were revealed by the scanning electron microscopy (SEM). The composite with 30 wt% sisal fibres gives excellent flexural strength, water absorption, and especially the wear resistance showing that it has the most superior bonding and adhesion of all the composites. In particular, the highest value 9.42 kJ/m2 of charpy impact strength is observed in the composite with 50 wt% sisal fibre. SEM micrographs of impact fractured and worn surfaces clearly demonstrate the interfacial adhesion between fibre and matrix. This work shows the potential of sisal fibre (SF) to improve the composite wear resistance and to be used in fibreboard.
The effect of temperature on weldline properties of injection moulded acrylonitrile butadiene styrene (ABS) reinforced with short glass fibres was investigated in tension between 25 and 100°C. Tensile modulus of both weld and unweld specimens increased linearly with increasing fibre concentration and decreased linearly with increasing temperature. It was found that the presence of weldline had no significant effect upon tensile modulus and this was reflected by weldline integrity factors in the range 0.98 to 0.95. Tensile strength of both weld and unweld tensile specimens increased nonlinearly with increasing fibre concentration and in the case of weldline specimens showed a maximum at fibre concentration of approximately 10% v/v. A linear dependence with respect to volume fraction of fibres was found for specimens without weldline for fibre concentrations in the range 0–10% v/v. The weldline integrity factor for tensile strength decreased significantly with increasing fibre concentration and increased with increasing temperature. The effect of temperature on tensile modulus and strength was satisfactorily modelled using the Kitagawa power law relationship..
Poly (St-MAn-APTES)/silica hybrid materials were successfully prepared from styrene (St), maleic anhydride (MAn) and tetraethoxysilane (TEOS) in the presence of a coupling agent 3-aminopropyltriethoxysilane (APTES), by freeradical solution polymerization and in situ sol-gel process. The TEOS content varied from 0 to 25 wt%. Fourier transform infrared spectroscopy and 29Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids (condensed siloxane bonds designated as Q1, Q2, Q3, Q4, with 3-aminopropyltriethoxysilane having mono-, di-, tri, tetra-substituted siloxane bonds designated as T1, T2 and T3). The results revealed that Q3, Q4 and T3 were the major microstructure elements in forming a network structure. The hybrid materials were also characterized by the methods of solvent extraction, Transmission Electron Microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for determining the gel contents, particle size and thermal performance. The results showed that gel contents in the hybrid materials were much higher, the SiO2 phase were well dispersed in the polymer matrix, silicon dioxide existed at nanoscale in the composites, which had excellent thermal stability.
Based on monitoring the γ process (the lowest temperature-relaxation) in polyacrylonitrile (PAN) by dynamic dielectric spectroscopy, new evidence for the formation of a charge transfer complex between bromine dopants and nitrile groups is presented. The experimental work is carried out on PAN and nitrile polymerized PAN with and without bromine doping and the effects of these factors on the γ process are measured. Nitrile polymerization results in diminishing of the γ process and in a 15% increase in its activation energy, whereas bromine doping produces splitting of the original γ process in PAN – coupled with a significant activation energy increase – and its complete disappearance in nitrile polymerized PAN. Both the splitting of the γ process and the higher activation energy reflect bromine-nitrile adduct formation..