Two categories of biodegradable materials
Biodegradable materials can be divided into completely biodegradable materials and destructive biodegradable materials according to degradation mechanism and destruction methods.
01
Completely biodegradable material
Completely biodegradable materials refer to biodegradable materials that can be decomposed by bacteria, fungi, actinomycetes and other microorganisms. It can finally be decomposed into CO2 and water under the action of bacteria or its hydrolase to return to nature, so it is called "green material". From the preparation method, it can be divided into three kinds: microbial fermentation method, chemical synthesis and natural polymer blending.
Microbial fermentation
Microbial fermentation refers to the biodegradable materials obtained through microbial fermentation using organic matter as a carbon source, mainly polyhydroxy fatty acid esters. Polyalkyl fatty acid ester (PHA) is an intracellular polyester synthesized by many bacteria. It has many excellent properties such as biodegradability, biocompatibility and edibility. It has played an important role in biomedical materials, tissue engineering materials, sustained-release materials, electrical materials and packaging materials.
The Procter & Gamble Company of the United States has successfully developed the PHA series products and their various applications as suture threads, non-woven fabrics and various packaging materials. At present, the global research of PHA is mainly focused on the use of its biodegradability, biocompatibility and other characteristics to develop applications in high value-added fields such as medical, pharmaceutical, and electronics.
Chemical synthesis
Chemically synthesized polymer degradable materials refer to biodegradable materials synthesized and manufactured by chemical methods. Most of them are aliphatic polyesters containing ester-based structures that can be degraded by microorganisms in their molecular structures. At present, the representative industrialized products are polycaprolactone (PCL), polysuccinate succinate (BS), and polylactic acid. (PLA), aliphatic polyester/aromatic polyester copolymer (CPE), etc.
Polylactic acid has excellent biocompatibility and absorbability, non-toxic, non-irritating, it can be completely decomposed into CO2 and H2O in nature, no pollution to the environment, is currently the most promising biodegradable polymer one. Polylactic acid has a wide range of uses and is currently used in biomedical polymers, textiles and packaging industries. Polycaprolactone (PCL) has excellent biocompatibility, memory and biodegradability, and its products are mostly concentrated in medical and daily use such as orthotics, sutures, bandages, and degradable plastics.
Natural polymer blending
Natural polymer biodegradable materials are materials made using biodegradable natural polymers, such as plant-derived biological materials and animal-derived chitin, as substrates to make the product degradable. Plant sources include cellulose, hemicellulose, lignin, starch, polysaccharides and hydrocarbons composed of cell walls; animal sources are mainly crustaceans such as shrimp and crabs. The main varieties are PHB/PCL gelatinized starch/PCL gelatinized starch/PHBV, etc.
Such degradable materials are rich in raw materials, can be completely biodegradable, and the products are safe and non-toxic, and people are paying more and more attention. However, natural polymer materials are completely biodegradable. However, its thermal and mechanical properties are poor and cannot meet the performance requirements of engineering materials. Therefore, the current research direction is to modify natural polymers to obtain valuable natural polymer degradation materials.
02
Biodestructive material
Biodestructive materials are at the material level. They are mainly degradable materials made by blending or copolymerization of natural polymers and general-purpose synthetic polymers. The combination methods are as follows:
(1) Use melting and solution blending methods;
(2) A polymer material is dispersed in an aqueous solution of another polymer to form a suspension system, and finally various composites are made;
(3) Disperse or dissolve natural polymer materials in a system that can undergo polymerization reactions, conduct homopolymerization and copolymerization reactions, and polymerize monomers in the system to obtain composite materials containing natural polymers;
(4) Properly degrade natural macromolecules under appropriate conditions (such as acidic or alkaline, etc.), and polymerize the degraded molecular segments with other monomers. Thus, a novel copolymer with biodegradable properties is prepared. The degradable materials made by blending or copolymerization of starch, cellulose, protein and synthetic polymers will be introduced below.
Starch-based materials
As a kind of natural polymer compound, starch has a wide variety of sources and low cost. And can be completely degraded in various natural environments. It is finally decomposed into CO2 and H2O and will not cause any pollution to the environment. Therefore, starch-based degradable materials have become the most researched and developed biodegradable material at home and abroad. It can be obtained by blending with other polymers or copolymerizing with monomers. Starch-based degradable materials.
In 1973, Griffin obtained the patent for starch surface modification filling materials for the first time. By the 1980s, some countries developed starch-filled biodegradable materials on the background of Grifn's patents. Filled starch materials are also known as biodestructive materials. Its manufacturing process is to add a certain amount of starch and other small amounts of additives to general materials and then process them into shapes. The starch content does not exceed 30%. The filling type starch material technology is mature and the production process is simple, and can be produced by slightly improving the existing processing equipment. Therefore, most of the domestic degradable starch material products are of this type.
Canadian St. Lawrence Starch Company has researched and produced a modified starch Ecostar masterbatch. It can be blended with polyethylene, polypropylene, polystyrene, polyvinyl alcohol and polyurethane to make biodegradable materials. The starch-based material developed by the United States Department of Agriculture is to add gelatinized starch containing 40%-60% water to EAA (ethylene acrylic acid). ) Is mixed to make agricultural mulch film. The starch grafted polystyrene developed by Purde University in the United States adopts cationic polymerization to effectively control the molecular weight and physical properties. Among them, the starch contains 20%-30% starch, and the graft polymer has the usual polystyrene Similar properties to ethylene. Can be used as bottles, films, etc. my country’s Taiyuan University of Technology Liu Shufu and others studied the graft copolymerization of potato starch and polyvinyl chloride. The Institute of Applied Chemistry of Jiangxi Academy of Sciences used starch and styrene graft copolymerization to make starch-based materials. Degradable membranes were explored.
Cellulose-based materials
There are also two preparation methods for cellulose-based plastics, one is blending, and the other is chemical modification of typical cellulose-based materials. There are several preparation methods: the blending of cellulose and chitosan, the blending of cellulose and protein, the blending of cellulose and its derivatives, the copolymerization of cellulose and polymer monomers, hemicellulose, lignin, etc. Blending and chemical modification methods can be used to prepare cellulose-based degradable materials. For example, Kyoto University in Japan can prepare light brown biodegradable materials by treating wood powder with lauric acid.
Protein-based materials
Although protein has good biodegradability, its thermal and mechanical properties are poor. Chemical treatment (including copolymerization) can improve its thermal and mechanical properties, but research in this area is still in the basic research stage.
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