Thermoplasticity esterified wood

The stress relaxation properties of SA-modified wood in media of different pH have also been studied (Nakano etal., 1990a,b, 1991 Nakano, 1993a,b). It was found that an increase in pH led to an increase in stress relaxation properties due to side chain ionization, with maximum swelling of the wood occurring between pH 5-8. In addition, cross-linking within the wood was achieved by treatment with bivalent or trivalent metal ions. The rheological properties of maleic acid esterified wood also show that thermoplasticity is imparted to the wood by such modification (Norimoto etal, 1992). 

The above results shown in Figs. 12 and 13 can be discussed in connection with the application of the thermoplasticized wood. The thermoplasticized wood can be used as material for molding, and as one way of utilization, can be used as blend composites with synthetic polymers. If this blending is made by grafting as shown above, two benefits can at least be pointed out (a) the thermoplasticity of wood materials is enhanced. (Better results can be obtained with esterified wood.) (b) the compatibility of the plasticized wood with synthetic polymers increases by the grafting. These factors are considered to be advantageous for preparing molded composites with excellent final properties. 

While untreated wood meal shows a thermal softening point of 260°C, esterified wood meals prepared in the N204-DMF-pyridine solution have a softening point of around 100 C or less and a thermal flow temperature of 220-250°C [98]. The flow temperature shows a tendency to decrease with increase in the C number of acyl group. This was first found by Shiraishi et al. [98] that wood meal is converted as a whole to thermoplastic material. In this case, a very high degree of acylation is not always required to provide wood with the thermally meltable property. The products become thermoplasticized materials when almost one-third of the hydroxyl groups in wood are acylated [99]. 

Matsuda and Ueda [27] also extensively investigated the esterification of wood in order to make a totally thermoplastic material. They esterified wood with a solvent by simply heating wood meal with succinic anhydride for 3 h at temperatures greater than 60°C. The wood meal was readily molded at 180°C under a pressure of 570 kg/cm for 10 min. The moldability of various esterified woods decreased in the following anhydride order succinic anhydride > maleic anhydride > phthalic anhydride. 

U.S. Pat. No. 6,903,149 [58] discloses a plastic-wood composite comprising 100 parts by weight of a thermoplastic resin such as PVC, polyolefin, polystyrene, a polyester resin, and a polyamide resin, 5-400 parts by weight of wood flour, and 0.05-20 parts by weight of a dibasic polyol ester having at least one hydroxyl group esterified with fatty acid. 

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