All issues / Volume 2 (2008) / Issue 2 (February)
Nanocomposites with polypropylene/clay/wood flour were prepared by melt compounding. Thermal, mechanical and morphological properties were characterized. The addition of clay, compatibilizer and wood flour considerably improved the thermal stability (i.e., decomposition and melting temperatures) of the hybrids. The tensile modulus and strength of most hybrids were highly increased with the increased loading of clay, MAPP and wood flour, compared to the hybrids without wood flour. The wide angle X-ray diffraction (WAXD) patterns showed the increased d-spacing of clay layers, indicating enhanced compatibility between PP and clay with the addition of maleated polypropylene (MAPP). The transmission electron microscopy (TEM) photomicrographs illustrated the intercalated and partially exfoliated structures of the hybrids with clay, MAPP and wood flour.
The aim of this study was to investigate the influence of incorporating Bis-EMA4 monomer into experimental Bis-GMA/TEGDMA-based resin luting agents on the bond strength to dentin. Seven mixtures were prepared with the following ratios (wt%) of Bis-GMA/TEGDMA/Bis-EMA4: 50/50/0, 50/30/20, 50/10/40, 50/0/50, 30/10/60, 10/10/80 and 0/0/100. Camphorquinone (0.4 wt%), N,N-dimethyl-p-toluidine (0.8 wt%) and hydroquinone (0.2 wt%) were dissolved in each mixture, which was loaded with silanated strontium glass fillers to a constant content of 60 wt%. Bond strength was evaluated by microshear testing (n = 10) on bovine dentin. Data were submitted to Analysis of Variance (p < 0.05). Modes of failure were classified under magnification (200×). Bond strength means (MPa), respective to each agent, were: 19.4, 19.8, 20.0, 19.1, 16.8, 18.7 and 17.8. No significant differences were detected among groups. Mixed failures were generally predominant for all materials. In conclusion, the addition of Bis-EMA4 presented no significant influence on the bond strength of the experimental resin luting agents to dentin.
In the present paper, grafting of methyl methacrylate (MMA) onto flax fiber was carried-out under different reaction condition such as in air (IA), under pressure (UP) and under the influence of micro-wave radiations (MWR). Maximum percentage grafting (41.7%) has been observed in case of graft copolymerization carried-out in air at 55°C followed by grafting under pressure (36.4%) at 0.8 MPa and under the influence of microwave radiations (24.6%) at 210 W microwave power. Graft copolymers were characterized with FTIR spectroscopy, scanning electron microscopy (SEM), thermal analysis (TGA/DTA) and X-ray diffraction (XRD). Thermal stability of flax decreases on grafting under different reaction conditions. In case of XRD studies, cellulose crystals are better oriented in flax fiber followed by Flax-g-poly(MMA)-MWR, Flax-g-poly(MMA)-UP and Flax-g-poly(MMA)-IA.
Interaction between anionic (and cationic) colloidal particles of silica having the particles diameters 12 and 22 nm with synthetic cationic (and anionic) polyelectrolytes of various nature and structure was studied by potentiometric, conductimetric spectroturbidimetric and viscometric methods in aqueous solution. It was shown that the complexation of silica nanoparticles with linear polyelectrolytes leads to formation of mostly stoichiometric interpolyelectrolyte complexes (IPEC) which precipitate from aqueous solution. Casting of water-soluble IPEC followed by thermal treatment gives thin composite films insoluble in water while ‘layer by layer’ (LbL) deposition of polyelectrolyte components onto silica sols leads to formation of multilayered nano- and microcomposites. The possible mechanism of formation of LbL multilayers consisting of silica sol (SiO2) ‘cores’ and polyethyeleneimine-polyacrylic acid (PEI-PAA) ‘shells’ was suggested. It was found that in diluted aqueous solution the radius of gyration, Rg and hydrodynamic radius, Rhmean of LbL particles are independent on LbL concentration and smaller than 100 nm. The zeta potential values of LbL particles are arranged between –10 and –30 mV. The average size of LbL particles estimated by scanning electron microscopy (SEM) is in the range of 200–500 nm. Thermal treatment of LbL multilayers followed by etching of (SiO2) ‘core’ by HF leads to formation of a series of spherical nanocavities and blob-like microcavities.
In this work, the effect of mold temperature variation on the short-term mechanical properties obtained from the tensile and Charpy impact tests, and the long-term mechanical properties obtained from dynamic mechanical loading and flexural creep of injection molded polybutylene terepthalate (PBT) are reported. It has been observed that the effect of changing the processing condition viz. mold temperature on the viscoelastic properties are more pronounced when their long-term behavior is tested. The tensile and impact properties showed only a negligible effect to the change in mold temperature. Further, analysis of the creep curves by applying a four-element Burger model presented a comprehensive understanding of their long-term viscoelastic behavior with respect to the change in mold temperature.
The impact and flexural strengths of epoxy-dicyclopentadiene bisphenol cyanate ester (EP-DCPDCE) hybrid thermoset as well as the interlaminar shear strength (ILSS) and flexural strength of the composites consisting of the hybrid thermoset and glass fabric were studied. It is found that the addition of epoxy resin (EP-51) can improve the mechanical properties, particularly, the impact strength of DCPDCE matrix and the ILSS of glass fabric reinforced composites. The improvements of the mechanical properties were obvious when the content of EP-51 is from 15 to 30 wt%. The investigations of the interphase of composites by scanning electron microscope (SEM) and dynamic mechanical analysis (DMA) confirm the improvement of mechanical properties of the composites. However the addition of EP-51 has negative effects on the thermal and dielectric property of the composites.
Flame retarded thermoplastic polymer compounds were prepared containing recycled rubber tyres, low density polyethylene, ethylene vinyl acetate copolymer and an intumescent additive system consisting of waste polyurethane foam and ammonium polyphosphate. The effect of the additives on the combustion properties was characterised by Limiting Oxygen Index, UL 94 and mass loss calorimetric measurements. The environmental impact was estimated by determining the gas components of CO2 and CO evolving from the compounds during the burning process using a gas analyser system constructed by coupling an FTIR unit to a mass loss calorimeter. The new material forms a thermoplastic rubber of excellent processability making it suitable for application in construction industry.
The thermal stability and kinetics of non-isothermal degradation of polypropene and polypropene composites filled with 20 mass% vigorously grounded and mixed raw rice husks (RRH), black rice husks ash (BRHA), white rice husks ash (WRHA) and Aerosil Degussa (AR) were studied. The calculation procedures of Coats – Redfern, Madhysudanan et al., Tang et al., Wanjun et al. and 27 model kinetic equations were used. The kinetics of thermal degradation were found to be best described by kinetic equations of n-th order (Fn mechanism). The kinetic parameters E, A, ΔS≠, ΔH≠and ΔG≠for all the samples studied were calculated. The highest values of n, E and A were obtained for the composites filled with WRHA and AR. A linear dependence between lnA and E was observed, known also as kinetic compensation effect. The results obtained were considered enough to conclude that the cheap RRH and the products of its thermal degradation BRHA and WRHA, after vigorously grounding and mixing, could successfully be used as fillers for polypropene instead of the much more expensive synthetic material Aerosil to prepare various polypropene composites.