Materials are the material basis for the survival and development of mankind as well as the core of technological progress.However, the application of polymer materials has penetrated into all aspects of human life.Data show that in 2013 the global plastic production exceeded 280 million tons, of which China's output More than 60 million tons, the consumption of more than 70 million tons.At present, emerging markets, plastic production and consumption continues to soar.As the natural bio-based polymer materials with traditional polymer materials do not have the green, environment-friendly, raw materials can be Renewable and biodegradable characteristics, so it has a good market prospects.Therefore, this article on the status of natural bio-based polymer materials industry, and the corresponding emergence of the latest product technology, performance and use for detailed introduction for the reader to understand.
First, bio-based polymer material profile
◆ 1 bio-based polymer materials
At present, the bio-based polymer materials are bio-based platform compounds, bio-plastics, functional sugar products, wood-plastic composites, and other products both daily life can often be found in daily necessities, such as packaging materials, disposable commodities, Also includes high-tech, high value-added drug controlled release materials and bone fixation materials, and human tissue repair materials and other bio-medical materials, etc. Can be divided into the following three categories:
(1) bio-based thermoplastic polymer materials: such as PLA, thermoplastic starch, fiber and composite materials;
(2) bio-based thermosetting polymer materials: such as epoxy resin, unsaturated resin, adhesives, etc .;
(3) bio-based polymer additives: such as flame retardants, plasticizers, nucleating agents, modifiers and so on.
◆ 2. The purpose and significance of bio-based polymer materials development
According to the data, nearly 99% of macromolecule materials come from petrochemical resources, but now petrochemical resources are facing an increasingly depleted crisis, and the environmental protection problem is getting worse.If using bio-based polymer material instead of ordinary plastic products, it can reduce 30% ~ 50% of the consumption of petroleum resources, while reducing carbon dioxide emissions by 50% ~ 80% .In this context, research and development of biodegradable bio-based polymer materials to replace petroleum-based polymer materials has urgent practical significance.In recent years In the active efforts of governments and related enterprises in various countries, bio-based polymer materials have made great strides.
Second, the natural bio-based polymer materials classification and introduction
As one of the important components of bio-based polymer material, natural bio-based polymer material refers to a polymer material that is blended and modified by natural organisms (including animals, plants and microorganisms, etc.) or other resources and has a wide range of sources, Rich reserves, renewable materials, recycling or degradation, but the general molding difficult, the main categories are as follows:
◆ 1 wood plastic composite material
WPC composites are mainly made of plastic materials (PP, PE, PVC, etc.) and their recycled waste plastics. By adding waste plant fibers such as wood flour, rice husk and straw Mixed into a new wood materials, and then by extrusion, molding, injection molding and other plastic processing technology to produce the plate or profile.The main features are: raw materials recycling, product plasticization, the use of environmental protection, cost-economy, recycling The
At the same time, plastic and wood as both water and corrosion of wood and texture of the two characteristics of wood, making it a good performance and very durable outdoor building materials (floors, fences, stools, gardens or waterfront landscape, etc.) Among the various templates used in the project, WPC template is the most suitable material for recycling and environmental protection at present. It has been adopted in many key construction projects. In 2015, WPC template application has exceeded 100 million square meters.
◆ 2. Starch-based plastic
Starch is a kind of natural macromolecule polymer, widely existed in plants such as corn, wheat, rice, potato, cassava etc. Because of its molecule contains a large number of hydroxyl groups, so starch macromolecules have strong interaction, leading to the original starch Difficult to melt processing, and in the process of blending with other polymers and poor compatibility with other polymers, but these hydroxyl esterification can occur, etherification, grafting, crosslinking and other chemical reactions, the use of these chemical reactions Starch chemically modified to reduce the hydroxyl of starch to change its original structure, thereby changing the starch corresponding performance, the original starch into a thermoplastic starch.Generally physical modification, esterification, transesterification or etherification, Crosslinking reaction, blending modified composite materials, such as blending modified copolymer.
Plastic wood composite materials for outdoor building materials
Starch-based plastic sources wide, cheap, renewable, in the soil and natural environment can be completely and rapidly degraded, non-toxic, pollution-free, odor-free, and degradation will not destroy the soil structure. At present, the typical thermoplastic starch plastic products For the film, it is transparent, soft, non-toxic features typical starch / degradable polymer composites starch / PVA alloy.
◆ 3. Cellulose and its derivatives plastic
Cellulose chemistry and industry began more than 160 years ago, is the main period of the birth and development of polymer chemistry.Cellulose macromolecule base ring is D-glucose β-1, 4 glycosidic bond composed of macromolecular polysaccharide, which Chemical composition of 44.44% carbon, hydrogen 6.17%, oxygen 49.39%, cotton is a high purity (98%) of cellulose.Cellulose plastic thermoplastics as one of the most potent plastics, has good luster, good transparency, Hardness, mechanical strength, good dimensional stability, and other characteristics, and has excellent heat resistance, electrical insulation, weather resistance and chemical properties.
Cellulose derivatives are generally white fibrous, granular or flaky, and various cellulose derivatives are obtained by different methods of high purity cellulose, usually with nitrocellulose, cellulose acetate, cellulose acetate butyrate, Acetic acid - cellulose propionate, ethyl cellulose, cyanoethyl cellulose, hydroxyethyl cellulose and other several.
Cellulose plastic is prepared by the above plant cellulose or cellulose derivatives of this natural polymer compounds, through chemical treatment, through chemical reactions, after adding various additives after the physical modification of a class of thermoplastics Common additives are: plasticizers, stabilizers, lubricants, fillers, colorants, solvents and so on.
Cellulose plastic can be injection, extrusion, molding, blow molding, machining and other processes can be made of car windshield, stationery, packaging films, military safety glass, daily necessities, camera parts, radio enclosures, military supplies, electrical insulation Parts and Medical Hygiene Products.
◆ 4. Protein plastic
Protein plastics are one of the most widely used natural bio-based polymer plastics in the field of biodegradable materials.At present, the main plant proteins that are used in biodegradable materials at home and abroad are soybean protein, corn protein, wheat protein , Sunflower seeds, etc., of which the most studied soy protein.At present, soybean protein biodegradable materials processing methods are two: one is wet processing, the soon-to-be modified protein dubbed solution, casting film, natural air Dry or heated drying molding; the other is dry-processed, that is modified soybean protein and a certain amount of plasticizer mixed evenly, under the action of mechanical force by extrusion, molding, blow molding or injection molding Methods and take the appropriate mold Preparation of degradable material products. Molding conditions are: molding pressure, molding time and molding temperature.
Soy protein is the most studied plant protein in biodegradable materials
Because of the large number of amide bonds (-CO-NH-) in the main chain of the soy protein molecule, the side chains in the molecule contain more water-absorbing amino acid residues (-NH2, -COOH), the material has a hard and brittle, highly water-absorbent Characteristics, so the preparation of materials should be modified on the raw materials.Currently, common methods for the modification of protein materials are physical modification, chemical modification, small molecule plasticization modification, blend modification, etc. These modification methods only change The higher molecular structure or conformation of the protein molecule has no effect on the primary amino acid sequence.The main purpose of the modification is to improve the hydrophobic and mechanical properties of the material and to improve the plasticity and processing fluidity of the material.
At present, the factors restricting the development of biodegradable soy protein plastics are mainly expensive and difficult to popularize; the mechanism of degradation of materials is not yet clear enough, and precise controllability of degradation needs to be improved; evaluation methods of biodegradability have not been unified yet Standard.The focus of the research at home and abroad mainly focuses on improving the processing technology and improving the mechanical properties of the materials above, some scholars have made use of soy protein to prepare a biodegradable material with good mechanical properties and certain water resistance.
◆ 5 lignin plastic
Lignin plastic is the use of wood plastic and resin, plasticizers, inorganic fillers, compatibilizers, pigments and other components for blending the preparation of composite materials. Lignin is a renewable natural polymer, in nature, lignin Reserves second only to cellulose, the annual output of 150 billion tons, with biodegradable, renewable, low-cost, non-toxic advantages, derived from the black liquor paper.
The plastic industry requires a large amount of fillers and enhancers every year. Compared with common inorganic fillers, the biggest advantage of lignin lies in its highly reactive functional group on the molecule. It is convenient to chemically bond other required functional groups Based on the commercial value of lignin in terms of physical, chemical, industrial output and plastics, it is of interest to develop lignin plastics, including lignin / PVC, lignin / phenolic resin (PF), lignin / Polyurethane (PU), lignin / polypropylene (PP), lignin / polyethylene (PE) and the like.
Currently, the focus of lignin plastics research is still compatibilization technology, how to easily and effectively improve the compatibility between lignin and resin, is the key to the large-scale use of lignin in the plastics industry; In addition, lignin The matrix is produced by graft polymerization to completely degrade polymer materials such as lignin grafted methyl methacrylate, and lignin as a monomer directly involved in the reaction, the synthesis of phenolic resins, polyurethanes, polyesters and polyimides are also In recent years the development of hot spots.
◆ 6. Chitin and derivatives Chitosan plastic
◇ 6.1 chitin
Chitin, also known as chitin, is widely found in lower plant fungi, cells of algae, shells of arthropod shrimp, crabs, maggots and insects, shells of shellfish, molluscs (such as squid, cuttlefish), and Cartilage, cell walls of higher plants, the annual biosynthetic resources up to 10 billion tons to 100 billion tons, is the second largest biological resource on Earth after the plant fiber. Chitin by nature in the chitinase, Enzymes, chitosanases, such as complete biodegradation, to participate in the ecosystem carbon and nitrogen cycle, the Earth's ecological environment plays an important regulatory role.
Chitin from the chemical structure analysis know that chitin is the only positive charge in nature, a natural polymer.Chitin in nature are mostly always with water-insoluble inorganic salts and proteins closely together.People In order to obtain chitin, the shell of crustacea is often prepared by chemical or microbial methods.At present, industrialized production often uses chemical methods, after acid-base treatment, remove calcium salts and proteins, and then use strong base to take off under heating conditions To acetyl can be obtained a very wide range of soluble chitin (chitosan).
At present, chitin is often extracted from abandoned shrimp and crab shells both at home and abroad. The chitin content in shrimp and crab shells is 20-30%, the content of inorganic substances (mainly calcium carbonate) is 40%, and other organic substances (mainly proteins) The content is about 30% .China is a large resource of chitin resources.On an offshore Zhejiang coast alone shrimp reached 670,000 tons, according to 40% of the waste can be calculated 1 million tons of chitin, resource potential is huge.Chitin and Polyvinyl alcohol with high barrier properties, the performance of the film can reach the performance of ordinary plastic film, can be biodegradable.
◇ 6.2 Chitosan plastic
Chitosan is a water-soluble product of chitosan which has been deacetylated with concentrated aqueous alkali to obtain (1,4) -2-amino-2-deoxy-β-D-glucan. White, slightly pearl luster, translucent flaky solid Chitosan is a cationic polymer, chemical stability, about 185 ° C decomposition, non-toxic, insoluble in water and lye, soluble in sulfuric acid, organic acids (Such as 1% acetic acid solution) and weak acid aqueous solution.Dissolved in dilute acid to form a viscous and transparent chitosan salt colloidal solution, then H + in the solution that is combined with the amino groups in the molecule to generate a positively charged polymer , Acylation, carboxylation, hydroxylation, alkylation, esterification (sulfation), aldimination, azidation, salt formation, hydrolysis, chelation, oxidation, chlorination, branching and cross-linking can occur Etc. Through the appearance (the appearance of the more white the better), degree of deacetylation (deacetylation higher the better) two indicators of chitosan identification.
Chitosan can be blended with other natural bio-based polymer materials into chitosan plastic, such as chitosan and cellulose blends, which can be used in the production of packaging materials, agricultural films, seedlings, etc. Chitosan and starch Films produced from blends of composite materials are insoluble in water and have high tensile strength and can be used in packaged foods.
Conclusion
At present, petrochemical resources are increasingly depleted and environmental issues are becoming increasingly serious. The use of degradable natural bio-based polymer materials instead of petroleum-based high polymer materials is an important way to solve energy substitution and an effective means to improve the ecological environment. Therefore, Very practical significance.Research and development of natural bio-based polymer materials a long way to go, which requires everyone to work together to actively promote its development.