SYNOPSISThis paper describes the development of a new crosslinked poly(methyl methacrylateacrylic acid) copolymer for potential applications in bone implants. This copolymer, comprising hydrophobic and hydrophilic components, has been designed to provide small amounts of controllable swelling strains at saturation when exposed to an aqueous saline environment. The volume fraction of the hydrophobic methyl methacrylate monomer to the hydrophilic acrylic acid monomer strongly influenced the swelling behavior of the copolymer. Two different cross-linking agents, allyl methacrylate and diethylene glycol dimethacrylate, were evaluated for their effectiveness in cross-linking and limiting the saturated swelling levels. The influences of the amounts of crosslinking agents and other processing parameters on the swelling behavior of the copolymer were studied using differential scanning calorimetry measurements, solubility tests, and swelling measurements in saline solutions. These measurements provided a good understanding of the structure of the copolymer, the effectiveness of the crosslinkers, the swelling mechanisms in this system, and the factors that strongly affect the swelling weight gain levels in this copolymer.
Purpose -To investigate a new approach for the prevention of lignocellulosic composites based on agro-fibres (e.g. sugar-cane bagasse) from the emission of toxic formaldehyde. Design/methodology/approach -Five organic polymer containing nitrogen-urea formaldehyde (UF) adhesive systems were used as bonding agents for bagasse fibres. The environmental performance of the lignocellulosic composites prepared were evaluated in terms of the effect of the organic polymers on the percentage of free formaldehyde in the adhesive system and the adhesion properties (static bending and water resistance properties) of the composite produced, in comparison with that prepared from un-modified UF. The nitrogen content of the polymer and the amount of organic polymers incorporated in the adhesive system were optimised using the 3D response surface methodology and the multi-linear regression technique. Findings -All investigated organic polymers (crude PAM-g-starch, PAM-g-starch, PAM, CE-starch and Cm-starch) were found to enhance the performance of the UF-adhesive for producing environmentally friendly bagasse-composite, whereas the reduction of free-HCHO in UF-adhesive systems ranges from 26 to 100 percent. The performance of the composite produced exceeded the ANSI requirements for Grade H-3 particle-board. Research limitations/implications -Despite the success in improving the performance (mechanical properties and reduction of free-formaldehyde) of the UF-adhesive and agro-composites, the polymers needed to be incorporated at a high percentage (12-20 percent) resulting in reduced water resistance of the product. Further investigation is needed to resolve this problem. Practical implications -The approach developed provided a simple and practical solution to enhancing the performance of waste agro-fibres and commercial amino adhesive in the production of high performance lignocellulosic composite. Originality/value -The organic polymers UF adhesive systems are novel bonding agents for agro-fibres and could be used in timber mills for production of particle-board and medium density fibre-board.
High molecular weight poly(ethylene sulfide) undergoes severe thermal degradation at the high temperatures (220–260°C) required for processing in injection‐molding equipment. Thermal degradation of the polymer is accompanied by gas evolution and a decrease in melt viscosity. Stabilization of poly(ethylene sulfide) can be effectively accomplished by addition of small concentrations of certain 1,2‐polyamines, preferably together with certain zinc salts as coadditives. Use of this stabilizer system inhibits thermal degradation to a remarkable extent, making it possible to mold the polymer at these high temperatures and obtain excellent physical and mechanical properties. Investigation of the thermal degradation process was carried out. The rate at which gases evolved from unstabilized poly(ethylene sulfide) resins of various molecular weights and preparative histories and from model compounds of the same organic backbone structure was measured at temperatures ranging from 220 to 260°C. Rate of gas evolution from the resins, irrespective of chain length or preparation, was found to be constant at 230°C. The evolved gases, analyzed by infrared spectroscopy and gas chromatography, contained ethylene. Nearly identical apparent activation energies were found for the gas evolution reaction from the resin and model compounds. The ΔE* values were in good agreement with ΔE* determined by other techniques, 58 ± 2 kcal/mole. This is about the energy requirement expected for the homolytic cleavage of a carbon–sulfur bond of the type present in a poly(ethylene sulfide) structure. The rate and analytical data indicate that the degradative mechanism at processing (molding) temperatures is primarily due to the organic structure of the polymer. A mechanism of thermal stabilization is proposed in which the polyamine and zinc salt, in presence of molten polymer at processing temperatures, form a two‐centered electron transfer complex, capable of reacting with both radicals of the homolytically cleaved bond, “healing” the scission, so to speak.
A novel formaldehyde-free system based on carboxymethyl cellulose was investigated as an adhesive for the production of composites from agricultural waste products such as bagasse. The system was characterized by spectroscopy, thermal analysis, and antimicrobial action. The mechanical and physical properties of the bagasse composites produced were determined. Factors such as water content during board formation, pretreatment of bagasse by water steam, amount of adhesive used, and pressure and temperature of pressing ORDER REPRINTS stage were studied to arrive at the optimum conditions for improving composite properties. The results obtained show that the novel formaldehyde-free adhesive system has higher antimicrobial action and was found to degrade rapidly with a relatively high amount of residual char in comparison with commercial adhesives. Bagasse composites made with the new adhesive show improvement in mechanical properties, as well as fire retardancy, compared with commercial-adhesive-bagasse composites. Nonisothermal analysis was used to study thermal stability, fire retardancy, and to determine activation energies of degradation.
The dead‐end radical polymerization theory of Tobolsky was applied to the bulk polymerization of isoprene. 2‐Azobisisobutyronitrile and benzoyl peroxide were used as initiators in the temperature range 60–90°C. Isoprene shows a dead‐end conversion under all the conditions we used. No Tromsdorff effect was observed in this system. The rate of decomposition of each initiator (kd)at different temperatures was obtained solely from the conversion‐time curve without further assumptions. The kd values thus obtained agree well with published data based on other methods. Knowing kd it was possible to compute (kp/k italict1/2)f1/2, where kp is the specific rate of propagation, kt the specific rate of termination, and f the efficiency of the initiator. This allowed comparison of the efficiency of benzoyl peroxide with 2‐azobisisobutyronitrile as free‐radical initiators in the bulk polymerization of isoprene. kp/k italict1/2 values for the azo‐initiated polymerization were also obtained and were found to be much lower for isoprene in comparison to reported values for styrene or methyl methacrylate. The high values of kp/k italict1/2 found for isoprene explain the low conversions obtained when isoprene is polymerized in bulk. From reported values of kp it was possible to calculate kt. This is the first time where the specific rate of termination of isoprene is reported. The rate constant kt was found to be 1.34 × 108 liters/mole‐sec. and is independent of temperature in the range 60–90°C. High kt values account for the low molecular weights obtained during the bulk polymerization of isoprene. The theory was also used to predict the course of isoprene polymerization as a function of time using previously determined values of (kp/k italict1/2)f1/2 and kd for the initiator used. The entire course of the conversion curves are well reproduced. The molecular weight distribution is also predicted as a function of conversion.
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