Iranian polymer journal
Volume:19 Issue: 1, 2010

Polymer biocomposites based on resorcinol-formaldehyde resin matrix, reinforcedwith pine needles were fabricated by compression moulding technique andfurther developed in our laboratory. Mechanical properties such as flexuralstrength, tensile strength, compressive strength and wear resistance of pine needlesreinforcedphenolic resin matrix based composites were evaluated to assess theprospect of using the lignocellulosic fibres as a new environmental friendly material inengineering applications. The addition of pine needles into the polymeric matrixpromotes a significant improvement in the composite properties. Effect of fibredimension on mechanical properties was evaluated. It has been observed that polymercomposites obtained by particle reinforcement exhibit better mechanical properties ascompared to short and long fibre reinforcement. Morphological and thermal propertiesof the polymer matrix and fibre reinforced green composites have also been studied. Incase of morphological features, the results clearly show that when polymer resin matrixis reinforced with fibres of different dimensions, morphological changes take placedepending on the fibres'' dimension. In case of thermal behaviour, the results obtainedclearly indicate that the presence of lignocellulosic pine needles affects the thermalstability of polymer matrix. The values of initial decomposition temperature and finaldecomposition temperature for polymer composite have been found to be in betweenthose of matrix and the fibre which indicate that the composite is slightly less stablethermally as compared to resin matrix. These composites were further subjected toidentical characterization tests such as swelling under different solvents, moistureabsorption and chemical resistance analysis, etc. It has been observed that particlereinforced composites exhibit higher resistance to swelling, moisture absorption andchemical resistance behaviour.

The effective chemical binding of polymeric chain with inorganic materials has acrucial impact on improving the integrative property of the composite. In thisstudy, potassium diperiodatocuprate (Cu3+) was used as an initiator to preparepoly(methyl acrylate)/TiO2 composites (PMA/TiO2) by in situ graft copolymerization inan alkaline medium. TiO2 particles were at first modified by aminopropyltriethoxysilane(KH550) before polymerization process in order to obtain the covalent bonds of PMAchain with TiO2 particles. The three synthetic parameters including the monomerconversion, grafting percentage and grafting efficiency were systematically evaluatedas functions of temperature, initiator concentration, pH and reaction time. The graftparameters were increased first and then decreased with increases in temperature,Cu3+ concentration and pH value of polymerization. It was also found from the experimental results that Cu3+ was a highly efficient grafting initiator for the copolymerization.The grafting efficiency was as high as 95% and the graft percentage was readilycontrolled within 460%. In addition, the highest graft parameters were observed at pH13.08 when the temperature was controlled at 30-40ºC. The structure of PMA/TiO2composite was characterized using the thermal gravimetric analysis (TGA), X-raydiffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The IRmeasurements clearly suggested that the PMA chains were effectively grafted ontoTiO2 surface. A single-electron-transfer mechanism was proposed to illustrate thegeneration of radicals by the redox reaction and the formation of PMA/TiO2 composite.

Fire behaviour of different types of expanded polystyrene (EPS) was studied withthe use of ISO 5660 cone calorimeter test method. The roles played by specimendensity and thickness on fire performance of the foam were examined. Therelationship between the fire properties of specimens, such as total-heat-release andheat-release-rate, with their densities and thicknesses was determined. The thicknessof specimens played two contradictory roles on fire behaviour of specimens. On theone hand, due to rapid melting the specimen received less heat energy relative to thecalibrated level and hence the ignition was delayed. On the other hand, theavailable mass for combustion reactions increased, which resulted in higher heat andsmoke release (both total and rates). This should be carefully considered in interpretationof fire test results of EPS foam in predicting its fire risk. It was revealed that bothaverage and the peak-of-heat-release-rates were directly dependent on density of thefoam and increased with it. A good repeatability for heat-release-rate was obtained inthis method, but this was not held for ignitability of specimens. The results showed thattime-to-ignition cannot be a characteristic value to make distinction between thestandard and fire retarded types of EPS in cone calorimeter test, but peak-heatrelease-rate values can be well utilized for this purpose.

The effect of organo-montmorillonite (OMMT) on the properties of acrylonitrilebutadiene rubber/polyvinyl chloride/OMMT (NBR/PVC/OMMT) nanocompositesis studied. Four different types of organo-modified OMMT were examined inNBR/PVC blend systems and an optimum type of OMMT (FMR11) was found bycharacterizing the mechanical properties of NBR/PVC/OMMT hybrids. Then,NBR/PVC/OMMT nanocomposites with various amounts of FMR11 were prepared bydirect mechanical blending. The dispersion of OMMT layers and morphology of thenanocomposites were determined by X-ray diffraction (XRD) and transmission electronmicroscope (TEM). Mechanical properties, solvent resistance and thermal stability ofnanocomposites were also investigated. TEM revealed that OMMT layers disperseuniformly in NBR/PVC matrix in nano-scale. XRD patterns revealed the intercalation ofpolymer chains inside the OMMT layer gallery. The tensile strength and tear strengthof nanocomposites based on 6.0 phr OMMT improved by 50.0% and 36.9%,respectively compared to gum NBR/PVC hybrids. Solvent resistance properties ofnanocomposites showed improvement with higher OMMT contents, which contribute tothe excellent barrier effect of OMMT layers.

In order to improve thermo-mechanical and flame-retardant properties ofpolyethylene, the polymer was cross-linked with vinyltriethoxysilane by usingbenzoyl peroxide as an initiator; and then various concentrations (0-35%) ofaluminium hydroxide (ATH) were incorporated. The effect of curing was observed withrespect to improvement in mechanical, thermal and burning properties. The three typesof blends (unmodified PE, uncured silane-grafted PE and silane-cross-linked PEloaded with ATH) in the form of heat pressed sheets, were characterized for theirmechanical properties like tensile strength and elongation-at-break. Solvent uptake,thermogravimetric analysis and burning behaviour of the blends were studied todetermine the effect of increased filler concentration, thermal stability and time requiredfor burning, respectively. It was observed that modification of polyethylene (PE) notonly mitigates the reduction in these properties in simple polyethylene but actuallyenhances them by modification. In the case of simple PE, the incorporation of fillercauses a marked deterioration in mechanical properties (elongation-at-break andtensile strength). However, approximately 20% increase in tensile strength and 50%control over the drastic decrease in elongation-at-break were observed for modifiedand filled polyethylene. The previously reported results show degradation of both theseproperties. In the proposed method, modification of polyethylene by silane crosslinkingimproves the burning time approximately 2.5 fold that of the same amount offiller. A clear difference in these properties for the incorporation of ATH to PE, uncuredsilane-grafted PE and silane cross-linked PE has been found. These properties followthe order of superiority as: silane cross-linked PE > silane-grafted uncured PE >physically filled PE. The influence of cross-linking and filler concentration onthermo-mechanical and burning properties due to efficient interaction of filler with PE,and that of silane cross-linked PE is discussed and analyzed.

The refractive index of poly(methyl methacrylate) (PMMA) thin films on glasssubstrates, prepared by spin coating method has been studied using aspectroscopic ellipsometry. Spectroscopic ellipsometry measurements of PMMAthin films were carried out at three angles of incidence, over the wavelength range of400-700 nm. Optical Cauchy model was used to obtain thickness of the prepared filmsalong with some optical constants. Each PMMA thin film shows a characteristicdispersion relation, although they all behave similarly. Refractive indices were found tobe in the range 1.49-1.53 with the maximum wavelength at 400 nm, and found toincrease with increasing molecular weight of PMMA, and consequently causing anincrease in film thickness. It was found that changing the molecular weight of PMMAand as a result the thickness of the films prepared made significant changes in bothreal (ε1) and imaginary (ε2) parts of the dielectric constant as a function ofwavelength. The ε1 and ε2 peaks near 570 and 500 nm, respectively, were shiftedtowards lower energy upon increasing molecular weight. The refractive index variationand the appearance of surface roughness after UV illumination were evident. Theroughness is modelled after fitting the spectroscopic ellipsometry data by usingBruggeman effective medium approximation assuming 50% PMMA and 50% voids. Itwas found that the UV illumination for one hour decreases the refractive index by 2 x10-3. The refractive index changes upon UV illumination might be attributed to differentfactors namely: (i) microstructural defects; (ii) decomposition of PMMA molecules; (iii)carbon-oxygen polarization; and (iv) dipole-dipole intermolecular interactions.

Self-assembly of low molecular weight oligomers through reversible hydrogenbond motifs can result in materials with polymer-like properties in bulk as well asin solution. The self-assembly supramolecular polymerization has become arapid growing area of research due to the temperature sensitive behaviour of thesupramolecular polymers. The synthesis and characterization of pyrimidinone(2-ureido-4[1H]-pyrimidinone, UPy) terminated poly(tetrahydrofuran) (PTHF(UPy)2), asupramolecular poly(tetrahydrofuran) is reported here. A low molecular weightpoly(tetrahydrofuran) diol (PTHF(OH)2) was functionalized with a strongly dimerizingUPy functional groups at both ends and their chemical structure as well as thematerial properties were studied. It is shown that PTHF(OH)2, which is a waxy materialat room temperature, behaves like thermoplastic elastomers upon functionalizationwith UPy end groups. PTHF(UPy)2 resembles a strong material with tensile strengthand tensile modulus of about 15 and 85 MPa, respectively. The rheological studiesrevealed that the supramolecular structure of poly(tetrahydrofuran) is stable uponheating up to about 80ºC. Above this temperature the supramolecular interactions startto dissociate, which are indicated by a sharp decrease in viscosity. Therefore,processing of PTHF(UPy)2 is possible at considerably low temperatures (slightly above80ºC).