دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و سوم شماره 6 (پیاپی 110، بهمن و اسفند 1389)

Cerium oxide (Ceria) nano particle, as photodegradation prevention agentwas studied in water-based polyurethane clear coat systems. Polyurethanecoatings show superior weathering resistance compared with acrylicmelaminesystems. However, any chemical change has detrimental effects on theproperty profile of PU coatings. Coatings containing various amounts of ceriumoxide nanoparticles were prepared and their weathering resistance was evaluatedusing simulated UV cabinet. To this end the extent and mechanism of degradationwas studied utilizing UV-Vis and FTIR-ATR spectroscopy as well as DMTA analysis.The results revealed that Ceria nano particles with concentration of 1.44 % (wt)absorb beyond 92.5% of UV light of UV-B region and showed an efficiency of 2000times as of organic UV absorbers

4-Chloromethyl styrene homopolymer and its copolymers with styrene wereprepared from their corresponding 4-chloromethyl styrene and styrenemonomers at 1:0, 1:1, 1:3 and 1:5 mole ratios. These homo- and copolymerswere synthesized by radical polymerization in presence of AIBN as initiator and drytoluene as solvent. Then, chloromethyl groups were converted into azidomethylgroups on the homo- and copolymers by substitution nucleophilic reaction in thepresence of sodium azide (NaN3) and dry dimethylformamide (DMF) as solvent.Finally, poly(para-amino styrene) homopolymers with different mole ratios of aminogroup on the polymer chain were prepared by reaction of Schmidt rearrangement inthe presence of 3-fluoromethane sulfonic acid from the homopolymer and its corresponding styrene copolymers having all azido methyl groups. Structures of theobtained homopolymers and copolymers were characterized by FTIR, 1H NMR, and13CNMR spectroscopy. Solubility of the homopolymer and copolymer products wastested in some organic solvents.

During the past two decades the use of lignocellouse fibers in reinforcingcomposites has attracted much research activities. In the present work,date palm fiber was used for production of composites compatible withliving environment. The fibers were pre-treated chemically to remove impurities. Inorder to verify and compare the effectiveness of the pretreatment methods, lignin,ash, moisture adsorption, diameter and tensile strength of the raw and treated fiberswere considered in all determinations. Some chemical contents of the treated fiberswere also estimated by FTIR method. The heating characteristics of the fibers wereevaluated using simultaneous thermal analysis (SAT) technique. The treated fiberswere mixed with HDPE by mass proportions of 10, 20 and 30% of the fibers in twotypes of fine and coarse sizes. Composite flower pots were prepared from the formulationsby extrusion process. The mechanical properties of the composites includingtensile strength, modulus of elasticity, strain, and impact strength were measuredby standard ASTM methods. Statistical analysis of the data revealed that the treatedfibers had smaller diameters containing lower levels of lignin and ash though havingsignificantly higher tensile strength, heat resistance and moisture adsorption. Theresults also indicated that by increase in fibre size the tensile strength, modulus ofelasticity and moisture adsorption of the composites are increased and their strainand impact resistance are decreased. The composites prepared using fine fibersshowed higher tensile strength, modulus of elasticity and impact strength but theirmoisture adsorption and elongation were significantly lower.

Nanoclay/triphenyl phosphate hybrid system was employed to examine thefire retardancy and mechanical properties of PC/ABS blends. Each of thepolymers and their blends are widely used in the automotive, electrical andelectronic industries. Because most thermoplastics are easily combustible they needto be flame retarded to reduce the burning rate especially in the initial phase of a fireincident. The effect of nanoclay on the fire resistance of nanocomposites has been thesubject of many research works. Nanosize clay particles improve the fire performanceof composites with no significant effect on the ignition ability and extinguishingtime. The improvement in flame retardancy of composites has been observedonly when nano size species are present with conventional flame retardant additives.Such combinations may result in either a desired level of flame retardancy lower thanthe normal conventional level with matrix property retention. In this study, the sampleswere prepared via a direct melt blending process in a twin-screw extruder, andthe processing temperature was set at 200-250oC. The effects of nanoclay/triphenylphosphate hybrid system on the fire retardancy of PC/ABS blend were assessed bycone calorimetry, LOI (Limited Oxygen Index) and UL94 (UnderwritersLaboratories), and tensile and impact properties of the composites were determined.The synergistic effect of nanoclay on flame retardancy of TPP has been observedfrom the fire test and the mechanical properties were improved

The effects of chitosan/biopolymer (C/P) and nanohydroxyapatite/ biopolymer(nHA/P) weight ratios on particle size and its uniformity, cross-linkingdensity and NH2 content of nano-hydroxyapatite/chitosan/gelatin (nHA/C/G) microspheres were investigated. Microspheres were fabricated using water-in-oil emulsion. Cross-linking of microspheres was performed using water soluble carbodiimide. Particle size and its uniformity were evaluated using an optical microscope. The morphology of microspheres was studied by scanning electron microscopy. The obtained data from particle size measurements revealed that increments in C/P ratio increased the particle size while reducing its uniformity, and increased the NH2 content and cross linking density of the microspheres. It was shown that incremental increase in nHA/P ratio increased the particle size and its uniformit and reduced the NH2 content and cross-linking density of the microspheres.Morphological studies showed that the fabricated microspheres had spherical shapein medium level of C/P ratio and nHA/P ratio. However, increasing inchitosan/biopolymer ratio induced some micro-cracks into the structure of microspheres

In suspension polymerization, particle size distribution of polymer is the outcome of dynamic equilibrium between the break up and coalescence phenomena. The rates of break up and coalescence and consequently polymerization stability depend on several parameters, the most important of which are type and concentration of stabilizer. In this study, the effects of type and concentration of stabilizer, concentration of initiator and temperature on the average particle size and its distribution in suspension polymerizationof styrene were experimentally studied. The results showed that polymeric stabilizers, polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), are more effective than tricalcium phosphate (TCP) as an inorganic stabilizer in reducing coalescence and achieving narrower particle size distribution. By increasing the stabilizer concentration, average particle size was reduced, while by increasing the initiator concentration, the average particle size andits distribution increased. Lowering polymerization temperature led to smaller average particle size with its narrower distribution

Industrial production of thermoset composite components involves the applicationof a vacuum bagging and autoclave pressure to minimize void percentage, usually to less than 5%. Phenolic resin systems generate water as a reaction byproduct via condensation reactions during curing at elevated temperatures. In this paper, vacuum bagging and simple manufactured autoclave curing systems are used for manufacturing of asbestos/phenolic composites and the effects of processing conditions on manufactured composites are investigated. The traditional single-vacuumbag process is unable to manage the volatiles effectively, resulting in inferior laminates having voids. The autoclave process cure cycle (temperature/pressure profiles) for the selected composite system is designed to emit volatiles during curing reactions effectively and produce composites with low void contents and excellent mechanical properties. Laminate consolidation quality is characterized by optical photomicrography for the cross-sections and measurements of void content and mechanical properties. The void content of phenolic composites as opposed to other composites increases as pressure increases up to 3 bar and it is then decreased beyond it. A product of 124% lower void content, 13% higher density, 24% higher flexural strength and 27% higher flexural modulus can be fabricated in composites obtained by autoclave processing.