| 摘要 |
A heat- and impact-resistant plastic composition comprises cellulose crystallite aggregates bonded together by mechanical interlocking and intermolecular bonding forces and a minor amount of a high-melting, moisture resistant resin to give a product of density 1.2-1.56. Specified resins include polytetrafluoroethylene, polyethylene, polypropylene, unvulcanized polyisobutylene, furan polymers, silicones, poly-formaldehyde, polyamides, polyurethanes, phenol formaldehyde resins, alkyds, casein and zein, and epoxy resins. Cellulose crystallite aggregates are obtained from the acid-insoluble portion of the product made by controlled acid hydrolysis of cellulose, preferably with dilute hydrochloric acid, and comprise at least 95%, generally 97-99%, cellulose. Suitable raw cellulosic materials which may be so hydrolyzed include ramie, cotton, and bleached sulphite and bleached sulphate wood pulp. The cellulose crystallite aggregates may be first mechanically disintegrated, and then formed into the plastic materials by pressure. In preferred methods:-(1) the aggregates are attrited in the presence of a liquid medium to form particles of from less than 1 to 300 microns in size, and the wet product is pressed at room temperature under at least 5,000 p.s.i. while removing at least a part of the liquid therefrom, and the pressed material dried. (2) The attrition step is omitted, the aggregates being merely pressed while wet at room temperature under at least 5,000 p.s.i. while removing at least a part of the liquid therefrom, and then dried. (3) The pressing step is omitted, the aggregates being merely attrited in the presence of a liquid medium to form particles of from less than 1 to 300 microns in size, and the attrited aggregates dried. The product of (1) and (2) is in the form of a hard mass, that of (3) in the form of a gel which on further drying becomes a hard mass. Porous products may be made by forming a gel of the crystallite aggregates, introducing air thereto, and then pressing and drying. Suitable liquid media include water, aqueous mixtures comprising di-tri-and polyhydric alcohols e.g, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and glycerol. Other suitable components of the aqueous mixture include glycol ethers e.g. 2-methoxyethanol, 2-ethoxy-ethanol, and 2-butoxyethanol, and the monomethyl, monoethyl and monobutyl ethers of diethylene glycol, polyoxyethylene glycols of molecular weight 200-4,000 e.g. methoxy polyoxyethylene glycols; esters of polyoxyethylene glycols of molecular weight 200-6,000 and diesters of the latter glycols of molecular weight 1,540-6,000; alkyl and alkaryl ethers of poly-oxyethylene glycols, polyoxy propylene glycols of molecular weight 150-425, water soluble polyoxyalkylene glycols containing recurring oxyethylene and oxypropylene groups, water-miscible alcohols, organic acids, esters, aldehydes ketones, ethers and oxides. These compounds may be employed per se as liquid media, particularly where they are both water soluble and liquid at room temperature. The plastic material so made may have a density in the range 1.2-1.57, be non-melting, have a horn-like appearance and smooth gloss surfaces, and be translucent. Specifications 231,431, 874,945 and 970,111 are referred to.ALSO:A heat- and impact-resistant plastic material comprises cellulose crystallite aggregates bonded together by mechanical interlocking and intermolecular bonding forces. Cellulose crystallite aggregates are obtained from the acid-insoluble portion of the product made by controlled acid hydrolysis of cellulose, preferably with dilute hydrochloric acid, and comprise at least 95%, generally 97-99%, cellulose. Suitable raw cellulosic materials which may be so hydrolysed include ramie, cotton, and bleached sulphite and bleached sulphate wood pulp. The cellulose crystallite aggregates may be first mechanically disintegrated, and then formed into the plastic materials by pressure. In preferred methods:-(1), the aggregates are attrited in the presence of a liquid medium to form particles of from less than 1 to 300 microns in size, and the wet product is pressed at room temperature under at least 5000 psi while removing at least a part of the liquid therefrom, and the pressed material dried. (2) The attrition step is omitted, the aggregates being merely pressed while wet at room temperature under at least 5000 psi while removing at least a part of the liquid therefrom, and then dried. (3) The pressing step is omitted, the aggregates being merely attrited in the presence of a liquid medium to form particles of from less than 1 to 300 microns in size, and the attrited aggregates dried. The product of (1) and (2) is in the form of a hard mass, that of (3) in the form of a gel which on further drying becomes a hard mass. Porous products may be made by forming a gel of the crystallite aggregates, introducing air thereto, and then pressing and drying. Suitable liquid media include water, aqueous mixtures comprising ditri- and polyhydric alcohols e.g. ethylene glycol, triethylene glycol, propylene glycol and glycerol. Other suitable components of the aqueous mixture include glycol ethers e.g. 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol, and the monomethyl, monoethyl and monobutyl ethers of diethylene glycol, polyoxyethylene glycols of molecular weight 200-4000 methoxy polyoxyethylene glycols; esters of polyoxyethylene glycols of molecular weight 200-6000 and diesters of the latter glycols of molecular weight 1,540-6,000; alkyl and alkaryl ethers of polyoxyethylene glycols, polyoxy propylene glycols of molecular weight 150-425, water soluble polyoxyalkylene glycols containing recurring oxyethylene and oxypropylene groups, water-miscible alcohols, organic acids, ester, aldehydes, ketones, ethers and oxides. These compounds may be employed per se as liquid media, particularly where they are both water soluble and liquid at room temperature. The plastic material so made may have a density in the range 1.2-1.57, be non melting, have a horn-like appearance and smooth glossy surfaces, and be translucent. A minor amount of a high-melting, moisture resistant resin may be incorporated in the material to give a product of density 1.2-1.56. Specified resins include polytetrafluoroethylene, polyethylene, polypropylene, unvulcanized polyisobutylene, furan polymers, silicones, polyformaldehyde, polyamides, polyurethanes, phenol formaldehyde resins, alkyds, casein and zein, and epoxy resins. Specifications 231,431, 874,945 and 970,111 are referred to. |
