Iranian Polymer Journal
Year:2007 | Volume:16 | Issue:4 (82)|Papers Count:7

The overall mechanical properties of composite materials are dependent on the mechanical response of individual constituents and their interactions while they may be relatively easy to determine. This paper represents a simulation process by which the cyclic stresses and fatigue loadings on its constituents could be predicted for an under fatigue loading lamina. Hence, the unidirectional composites fatigue would be studied through its constituents. The proposed model introduces a new coupled stiffness/strength technique by relating lamina stiffness to the stress field in its constituents. Therefore, the stress field and strength considerations in its constituents could be studied when the lamina stiffness is determined by a non-destructive process. For representing a complete description of the constituents’ properties and their interactions, the effect of fibre/matrix interface debonding was introduced into the model. A number of experiments are conducted to verify the simulated relations. The comparison of theoretical and experimental predictions shows that the results are satisfactorily in good agreement.

Unsaturated polyester resin, synthesized from glycolyzed product of poly (ethylene terephthalate) (PET) waste was combined with rice husks to form rice husk (RH)/polyester composites. PET from post-consumer soft drink bottles was recycled through glycolysis, followed by polyesterified with maleic anhydride and then cross-linked with styrene to produce a formulation for the resin. Characterizations of the synthesized resin were performed by hydroxyl and acid values determinations and Fourier transform infra red (FTIR) technique. The FTIR result for the prepared resin showed that cross-linking between polyester chain and styrene as cross-linkable monomer occurred at their unsaturated active sites. The effects of filler loading and surface modification of rice husks on the mechanical properties and water absorption of the composites were also investigated. It has been observed that the increasing filler loading resulted in reduction of tensile strength, elongation-atbreak and impact energy but increased tensile modulus, hardness and water absorption. At similar filler loading, alkalized filler composite has higher mechanical properties. This observation was well supported by the SEM investigations of the fracture surfaces.

Asymmetric blend hollow fibre membranes were made from a new castng dope containing poly(vinylidene fluoride) (PVDF)/thermoplastic polyurethane (TPU)/ N,N-dimethylacetamide (DMAc )/polyvinylpyrrolidone (PVP). The  separation property, microstructure, crystalline phase of membranes, and membrane strength were characterized by bovine serum albumin (BSA) retention experiments, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy- attenuated total reflection (FTIR-ATR), differential scanning calorimetry (DSC) and tensile testing, respectively. PVP at low concentration (≤3 wt%) was a significant demixing enhancer which thermodynamically controlled the phase inversion process, improved flux, reduced α-form crystal structure, and decreased crystallinity of PVDF in membranes. At high concentration of PVP (>3 wt %) due to viscosity buildup, kinetic hindrance overwhelmed the thermodynamic factor which suppressed the formation of macrovoids, reduction of flux, and increase in crystallinity of PVDF in membranes.

Weathered coal (WTC) modified asphalts with improved storage stability are prepared by incorporating styrene-butadiene rubber (SBR). The effects of WTC and SBR/WTC are studied on the storage and physical properties, and morphologies of the modified asphalts. It is found that the WTC has marked effect on the increasing of softening point at the content of 3 wt% while SBR has significant effect on the low temperature (5ºC) properties and improvement of aging resistance at SBR content of 4 wt% in the WTC and SBR/WTC modified asphalts. The morphology of SEM and TEM photographs show that WTC was dispersed relatively uniform in asphalt which indicates compatibility and storage stability are improved by producing a homogeneous phase in modified asphalts. The FTIR analysis show new weak peak areas in modified asphalts indicating physical alteration is the main changes in modified asphalts.

Schiff base oligomer of 2-[(phenylimino) methyl] phenol (2-PIMP) was synthesized via oxidative polycondensation reaction in an alkaline  medium by using air (O2) as oxidant. Oligomer-metal complex compounds were synthesized from the reactions of oligo-2-[(phenylimino) methyl] phenol (O-2-PIMP) with Co+2, Ni+2, Cu+2, Cr+3, Pb+2, and Zn+2 ions. While synthesized Schiff base oligomer was soluble in most common organic solvents, its metal complexes were only soluble in dimethylsulphoxide. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrochemical energy gaps (E´g) of monomer, oligomer, and oligomer-metal complexes were calculated from oxidation and reduction onset values. Also, optical band gaps (Eg) of monomer, oligomer, and oligomer-metal complexes were calculated from their absorption edges. Conductivity measurements of doped and undoped Schiff base oligomer and oligomer-metal complexes were carried out by electrometer at the room temperature and atmospheric pressure and were calculated by four-point probe technique. When iodine was used as doping agent, conductivity of oligomer and oligomer-metal complexes were observed to be increased. The weight losses of 2-PIMP, O-2-PIMP, O-2-PIMP-Co, O- 2-PIMP-Ni, O-2-PIMP-Cu, O-2-PIMP-Cr, O-2-PIMP-Pb, and O-2-PIMP-Zn were found to be 100.00%, 79.09%, 68.28%, 65.97%, 51.33%, 70.14%, 54.13% and 66.77%, respectively, at 1000°C by using TG analyses.

The prediction of the elastic modulus of short natural fibre hybrid composites has been investigated by using the properties of the pure composites through the rule of hybrid mixtures (RoHM) equation. In this equation, a hybrid natural fibre composite assumed as a system consisting of two separate single systems, namely particle/polymer and short-fibre/polymer systems. However, there is no interaction between particles and short fibres. Polypropylene was used as the polymer matrix and 40-80 mesh kenaf fibre and 60-100 mesh wood flour were used as the fibre and the particulate reinforcements, respectively. Hybrid composites were produced by kenaf fibre/wood flour ratios of 40:0, 30:10, 20:20, 10:30, and 0:40. Maleic anhydride and DCP have been also used as the coupling agent and initiator, respectively. Mixing process carried out in an internal mixer at 180°C and 60 rpm. The rule of hybrid mixtures (RoHM) equation has been employed using the weight and volume fractions of the reinforcements. The relationship between experimental and predicted values was evaluated and the accuracy of the estimation of the model was controlled. The results indicated that RoHM equation is able to predict the elastic modulus of the composites. The comparison between experimental and predicted values showed that they are in good agreement.

The influence of poly (vinylpyrrolidone) (PVP) concentration on the peel strength of an acrylic pressure-sensitive adhesive (PSA) has been studied as a function of the adhesive thickness. Different amounts of PVP (2-30% w/w) were mixed thoroughly with an acrylic PSA. Films with different thicknesses (10, 40, and 70 μm) were prepared by casting the formulation on a poly(ethylene terephtalate) film. Peel tests were carried out by adhesive-coated tapes of 25 mm width on the stainless steel substrate at least for three samples. The samples were investigated by Fourier transmittance infrared (FTIR) spectroscopy technique and surface tension and viscoelastic properties measurements. The peel strength values are directly dependent on the thickness of adhesive. Also, results showed that due to the polar part of blend in 2 %w/w PVP, the peel strength has the maximum value. At higher concentrations of PVP, due to its surface migration, reduction in peel strength was more pronounced. The parallel investigations on the viscoelastic properties of blends showed that the storage modulus shifts to higher values at higher concentrations of PVP. Therefore, the bonding step becomes difficult and the peel strength decreases significantly.