Iranian polymer journal
Volume:20 Issue: 12, 2011

Amodel is introduced to describe the erosion rate of random short carbon fibrecomposites exposed to high speed hot gas flow. A mathematical equation isderived to calculate the erosion rate of the composite using combined solutionof the heat conductivity, filtration and kinetic equations of reactions which occursimultaneously in a pyrolysis process. The fibre orientation distribution density functionhas been employed to determine the mechanical erosion of the composite as well asits chemical erosion and to evaluate the fibres angles with respect to their flowdirection. The model describes composite erosion rate as a function of compositesurface temperature, hot gas pressure head applied on the material and thethermo-physical properties of the fibres and resin. The DSC and TGA techniques havebeen employed to measure the ablation kinetic parameters. The thermal conductivitycoefficients of the composites have been obtained by Cussons thermal conductivityapparatus. To examine the validity of the results obtained by the model, a series ofexperiments were carried out using short carbon fibre/phenolic resin compositesamples in an oxyacetylene torch. The results obtained from the model are totally inaccordance with the experimental data collected from the oxyacetylene flame tests.This model can be effectively used in the design of thermal protection shields, for bothmaterial selection and calculation of the materials thickness.

For the first time, rare earths were utilized to modify silica (SiO2) for improving theink-receiving properties of silica/PVA (polyvinyl alcohol) composite films whichwas coated onto PET (polyethylene terephthalate) substrate. Fourier transforminfrared spectra, XPS, scanning electron microscope, Brunauer-Emmett-Teller (BET)surface area measurement, contact angle and mechanical strength tests were used tocharacterize silica and SiO2/PVA composite films before and after modification by rareearths. The results indicated that the rare earths can effectively modify silica byincreasing the oxygen-containing groups, decreasing the pore size and cumulativevolume of pores, and narrowing the pore size distribution. The possible mechanismduring rare earth-modification of silica may be due to the breakage of Si-O-C bondswhich generates the carbon radicals combined with dissolved oxygen in the solution toform C-O/C-OH bonds. However, the detailed reaction mechanism still needs to beinvestigated and clarified in the future because of the complexity during the reaction.The characterization of SiO2/PVA films illustrates that silica content, compared to rareearth treatment time, has stronger effects on the hydrophilicity enhancement of thefilms. The tensile strength of SiO2/PVA films rapidly increased from 46.8 MPa to72.6 MPa when increasing the rare earth treatment time from 0 to 10 h. The ink-receivingproperties of SiO2/PVA films were thoroughly examined which illustrated thatmodification of SiO2 by rare earth up to 10 h can significantly enhance the ink-receivingproperties of the composite films in terms of image quality, desiccation time of inkand mechanical strength of films with the optimum SiO2/PVA ratio of 0.3 (by weight).Besides, the thermal stability of composite films containing rare earth modified silicawas excellent. Therefore, the SiO2/PVA composite films containing rare earth-modifiedsilica seem to be promising materials for high-performance applications.

Phenolic/glass prepregs are widely used in manufacturing of structuralcomposites. In this work, four types of glass/phenolic prepregs, each with a resincontent of about 40 wt% were prepared by using resole and novolak phenolicresins and satin glass fibre fabric. They were B-staged or pre-cured at 100°C, 110°Cand 120°C in a laboratory-scale prepreg production machine at different processingconditions. The manufactured prepregs were characterized in terms of their volatilecontent, resin content, conversion or the degree of pre-cure, tack and flow behaviourto provide qualitative and quantitative assessments of prepreg processing, structureand properties. The optimum processing conditions were determined and the resultsshow that the level of pre-cure or conversion was in the range of 2 to 55% havingsignificant effect on tack and flow properties of the prepregs. The resole prepregcontaining 15% novolak resin (Re15N) showed the maximum tack of 19.8 kPa whichwas found to be at 6.5% of pre-cure. Nonetheless, the volatile content of prepreg wasvery critical and had a dual effect on tack and processing condition. We studied therheological properties of these prepregs by using a parallel plate rheometer. Thenovolak prepreg displayed a distinct rheological behaviour and by using a mixture ofboth resole and novolak resins a suitable processing condition was achieved.

Fabrication of polyvinylidene fluoride (PVDF) membranes from non-solventinduced phase separation process (NIPS) was studied. Particular focus wasgiven to the effects of triglycol and Tween80 as non-solvent additive (NSA) on thepolymer solution viscosity and membrane performance. The results showed that theviscosity of polymer solution increased after NSA addition, while it decreased withfurther incremental content of NSA. When VNSA/VS ratio approached its cloud pointvalue, the viscosity did increase again. Under the same concentration level, unlikeTween80, triglycol could lead to higher incremental value in viscosity. All themembranes obtained in this research work had dense outer surface and the pores insubsurface were formed by the gaps between spherulites. Similarly, the cross-sectionimages showed that, asymmetric structure consisted of a dense top layer and a poroussub-layer. The addition of triglycol promoted the formation of sponge-like structure andsuppressed the formation of finger-like structure. While, Tween80 promoted theformation of macrovoid structure and induced the disappearance of the finger-likepores. In addition, Tween80 improved the membrane surface hydrophilicity due to theexposure of the residual hydrophilic groups on the membrane surface. The addition ofNSA improved the water flux, especially for additive such as Tween80 (from 3.73L. (m2. h. 0.1 MPa)-1 to 440.25 L. (m2. h. 0.1 MPa)-1. After adding NSA into thepolymer solution, the breaking tenacity of the obtained membrane decreased, while theelongation-at-break increased.

PVC paste resin is an important poly(vinyl chloride) product which is applied inartificial leather fabrication, film applicator coatings and medical cathetersproduction. To make products flexible or just avoid adopting the debatedphthalates as plasticizers, four kinds of room temperature ionic liquids (ILs), [omim]PF6(1-octyl-3-methylimidazolium hexafluorophosphate), [bupy]PF6 (1-butyl-pyridinehexafluorophosphate), [C14mim]Br (1-tetradecyl -3-methylimidazolium bromide) and[C16mim]Br (1-hexadecyl -3-methylimidazolium bromide) were used as plasticizers forPVC paste resin, respectively. The mechanical properties, thermal and photo stabilitiesof plasticized PVC film samples were investigated by universal testing machine andTG/DTA methods. The results showed that the glass transition temperature (Tg) of20 wt% of a plasticized sample is lower than that of an unplasticized sample. Byincreasing plasticizer dosages from 10 wt% to 40 wt%, the tensile strength and elasticmodulus of the polymer decreased gradually though its elongation-at-break increaseddistinctly. The high temperature stability experiments showed that the decompositiontemperature and mass loss depend intensively on the composition and structure of theionic liquids. However, they were slightly affected by the plasticizer content. Moreover,the elongation-at-break measured data proved that ionic liquid-plasticized PVC filmsdisplay reasonable UV-stability