Thermoplasticized wood

Ogawa, T. and Ohkoshi, M. (1997). Properties of medium density fibreboards produced from thermoplasticized wood fibers by aUylation without adhesives. Mokuzai Gakkaishi, 43(1), 61-67. Ogiso, K. and Saka, S. (1993). Wood-inorganic composites prepared by sol-gel process II. Effects of ultrasonic treatments on preparation of wood-inorganic composites. Mokuzai Gakkasihi, 39(3), 301-307. 

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. 

Figure 9 Relationships between dimensional changes in the radical direction (p/ ) and water absorption (< )) of surface-benzylated wood. pR, Dimensional changes of radical direction 6, water absorption , untreated wood A, partially thermoplasticized wood O, thermoplasticized wood. (From Ref. 27.)...

Benzylated thermoplasticized wood surfaces showed good water resistance, but because of the aromatic construction of the benzyl group (Fig. 13), they showed high absorption of ultraviolet (UV) light. As a result of this, benzylated wood surfaces did not show good UV and weather resistance. Benzylated... 

Table 1 Some Properties of Etherified Surface Thermoplasticized Wood... 

The TMP process is similar to the RMP process except that after chip washing, a steaming vessel is inserted to achieve the thermoplasticization of the lignin in the wood. The production of thermomechanical pulps increased dramatically after the introduction of this method in the early 1970s. Because these pulps can be substituted for conventional groundwood pulps in newsprint blends to give a stronger paper, lower quantities of the more expensive, lower yield chemical pulps are required. 

Bonding of a reagent to the wood surface in order to thermoplasticize the surface for self-bonding. 

Ohkoshi, M. (1991). Bonding of wood by thermoplasticizing the surfaces II. Possible crossUnking of wood by the graft-copolymerizing of styrene onto allylated surfaces. Mokuzai Gakkaishi, 37(10), 917-923. 

Thermoplasticization of Cellulose and Wood by Graft Copolymerization and Acylation... 

Thermoplasticization of Wood by Heterogeneous Graft Copolymerization (Redox Initiation). A redox grafting method using ferrous sulfate-hydrogene peroxide as the initiator was conducted to copolymerize MMA to wood meal. The results of grafting are shown in Table III. 

Thermoplasticization of Wood by Graft Copolymerization in De-crystallized State. We have reported that wood can effectively be decrystallized without a weight-loss by treating with a non-aqueous cellulose solvent, the SO2-DEA-DMSO solution (11). Thus, use of the non-aqueous cellulose solvent as a reaction medium for the graft-copolymerization of monomers to wood was expected to result in products with branch polymers more uniformly distributed. The results obtained by the homogeneous grafting of cellulose (10) were expected to support this idea. 

It is clearly seen that the grafting is effective for preparing a thermally meltable material from the acetylated wood. Although irradiation to a total dose of 2 Mrad was applied for the grafting in this case, the low degree of irradiation as low as 1 Mrad or less has almost the same effect for the thermoplasticization of acetylated wood. 

This chapter deals with the chemical modification of wood by such methods as etherification, esterification, and thermoplasticization of wood, with emphasis on recent and new research in these fields. 

More recently, Kiguchi reported benzylation of wood particles with the solvent dilution and vapor phase methods for reducing the amount of benzyl chloride in the etherification agent [12]. In the vapor phase benzylation below the boiling point of benzyl chloride, greatly thermoplasticized particles could be produced after 2-4 h at 140°C. However, in the solvent dilution method, higher reaction temperatures and longer reaction times than those in the ordinary liquid phase method were found to be necessary to obtain the thermoplasticized particles. 

More recently, Ohkoshi et al. [103] studied the mechanism of thermoplasticization of wood by allylation. They considered that decrystallization of cellulose within wood during allylation permits the wood to soften thermally and the allylated lignin within wood increases the softening through acting as a plasticizer. 

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]. 

This chapter describes the surface activation and surface thermoplasticization of wood. The production of hot-melted and self-bonded boards through surface thermoplasticization of wood particles is also described. 

III. THERMOPLASTICIZATION OF WOOD SURFACES A. Thermoplasticizatlon of Wood Surfaces... 

The thermoplasticization of wood was subsequently reviewed in detail by Shiraishi [17]. 

Surface thermoplasticization of solid wood or particles is one of the more useful chemical modification techniques because most of the inherent properties of wood are retained. External plasticizers can only be applied to wood... 

The thermoplasticization of wood can be subdivided into two categories (Fig. 8) (1) the total thermoplasticization of wood meals to produce products that can be used as wood based adhesives or as moulded substitutes for synthetic plastics [21-23] and (2) partial thermoplasticization of wood. The development of hot-melted and self-bonded wood materials and methods of improving the surface properties of natural wood by partial thermoplasticization of wood are reviewed below. 

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