| 摘要 |
<p>Novel methods for manufacturing polyurea-cellulose composites are disclosed. The methods comprise impregnating a substantially delignified cellulosic fibrous material with a polyisocyanate resin. The resin can be applied to the cellulosic material either undiluted or diluted with up to about 20 % of an organic solvent miscible therewith, such as propylene carbonate. The resulting polyisocyanate-impregnated cellulose is pressurized at about 300 psig to about 1200 psig, such as by using either a preheated or a non-preheated press, until the core temperature of the impregnated cellulose reaches about 275 °F to about 350 °F. This combination of temperature and pressure cures the polyisocyanate, thus forming the polyurea-impregnated composite. Afterward, the composite is cooled while maintaining the pressure until the core temperature drops to about 100 °F to less than 212 °F. Then, the pressure is decreased to atmospheric. The method can also include, during the curing process, a temporary drop in pressure to atmospheric for about 4 seconds to about 10 seconds to release any gases entrapped in the polyisocyanate-impregnated cellulose during curing. Multiple-ply composites can be similarly made.</p> |
