Characterization of heat treated eastern redcedar (Juniperus virginiana L.)

The objective of the study is to investigate the influence of heat treatment on shrinkage, density, surface roughness, water absorption, diffusion coefficient, swelling and shear strength of eastern redcedar (Juniperus virginiana L.) samples. The anatomical structures of samples are also observed by scanning electron microscope (SEM). Specimens are exposed to temperature levels of 120 °C, 160 °C and 190 °C for time spans of 2 and 8 h. Based on the results of this study, dimensional stability in the form of shrinkage of the samples is improved by 2.68%, 1.40% and 1.49% for tangential, longitudinal and radial grain orientations as function of heat treatment, respectively. Heat treatment also enhances surface quality of the samples based on numerical values determined from stylus type of equipment. Water absorption, swelling values and diffusion coefficient of the samples are also reduced with heat treatment. Samples exposed to heat treatment have lower shear strength values, ranging from 25.12% to 52.67%, than those of control samples. It appears that all properties evaluated in this work are affected more pronouncedly as temperature and exposure time is increased.     

Properties of wood flour/expanded polystyrene waste composites modified with diammonium phosphate flame retardant

The objective of the study was to evaluate properties of waste plastic composite samples manufactured from expanded polystyrene waste (EPS) and sawdust containing diammonium phosphate (DAP) as flame retardant. Thermal degradation along with dimension stability and mechanical characteristics of the specimens as a function of DAP content were determined. The wood fiber/EPS composite modified with DAP content up to 20 wt% resulted in the best linear burning rate. The rate of thermal degradation of samples also substantially decreased while limiting oxygen index and char residual increased. Overall dimension stability in the form of water absorption and thickness swelling along with flexural characteristics of the samples were found comparable to those of commercial wood plastic composites. The wood fiber/EPS containing DAP showed high potential for use as wood composite products with adequate fire resistance. POLYM. COMPOS., 36:604–612, 2015. © 2014 Society of Plastics Engineers     

Chemorheology and thermomechanical characteristics of benzoxazine‐urethane copolymers

In this research, processability and some important thermomechanical properties of polybenzoxazine (BA‐a) modified with a highly flexible urethane elastomer (PU) are discussed. This copolymer has been reported to show synergy in its glass transition temperature and some mechanical properties thus provides a fascinating group of high temperature polymers with enhanced flexibility. The results reveal that a processing window of the BA‐a/PU mixtures is widened with the increasing urethane prepolymer fraction, that is, the liquefying temperature is lowered and the gel point shifted to higher temperature with the amount of the PU. Synergism in glass transition temperature (T_g) of this copolymer was clearly confirmed, i.e., T_g's of the BA‐a/PU alloys were significantly greater than those of the parent resins, i.e., BA‐a (T_g = 166°C) and PU (T_g = ? 70°C). In addition, flexural modulus was found to systemically decrease from 5.4 GPa of the neat polybenzoxazine to 2.1 GPa at 40% by weight of the PU. Flexural strength of the alloys also shows a synergistic behavior at the BA‐a/PU ratio of 90/10. Coefficient of thermal expansion of the polymer alloys were also found to show a minimum value at BA‐a/PU = 90/10. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Carbon fiber/epoxy vitrimer composite patch cured with bio-based curing agents for one-step repair metallic sheet and its recyclability

Vitrimers have gained a great deal of attention from researchers, yet research on its application is still lacking. This study, a novel bio-based vitrimer was developed from epoxy (EP) and bio-based curing agents, that is, cashew nut shell liquid (CNSL) and citric acid (CA), and then reinforced by carbon fiber. The vitrimers with different ratios of acid to epoxy (R ratio) at 0.30–0.40 contained ester and ether linkages. All EP/CA/CNSL vitrimers showed the stress relaxation over 70–100°C due to transesterification. The vitrimers were applied as polymer matrices for the carbon fiber composites and then used as repair patches. By using the carbon fiber-reinforced vitrimer with the R ratio of 0.30, patch repair on a damaged alloy sheet revealed that approximately 98% of the tensile strength of the damaged alloy sheet was recovered. The vitrimer can be dissolved from carbon fiber composite to recover carbon fiber. The recovered carbon fiber retained good tensile strength compared to the pristine composite. Based on this study, the EP/CA/CNSL vitrimers showed the comparable thermomechanical properties with the epoxy vitrimer cured by the petroleum-based curing agent. The vitrimer composite patch could therefore be an alternative new repair method to extend the service life of damaged structures.