Overview of the most popular biodegradable materia

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Overview of the types of biodegradable materials (Part 2)

3.1.2 double degradable starch plastics

in 1998, iffin proposed a new formula that can be both photooxidative degradable and biodegradable, that is, in the mixture of LDPE and corn starch, the oxidation promoter masterbatch composed of unsaturated hydrocarbon polymers, transition metal salts and heat stabilizers was introduced. Researchers assume that starch is first biodegradable, while LDPE matrix is hollowed out, increasing the surface area/volume ratio. Under the initiation of sunlight, heat, oxygen, etc., chemically unstable accelerators will undergo self oxidation, generating free radicals that attack the molecular structure of PE, reducing the molecular weight of LDPE, and then biodegradation can occur. The main products developed abroad include "ecostar plus" of ecostar company in the United States, "polygrade III" of ampact company, and the improved "poly clean" of ADM company; In addition, Swiss pivag company, British colurstyle company and Canadian St Lawrance company also produce double degradation masterbatch. Its products mainly include shopping bags, garbage bags, mulching films, tableware and food bottles. Because photosensitizer masterbatch and starch masterbatch are mainly used? The controllability and complete degradability of the composite masterbatch prepared by Kunming are not ideal

3.1.3 all starch thermoplastic

in order to be truly biodegradable, some companies have increased the starch content in the materials by 60%~70%, and the other components also use degradable raw materials. The representative products entering the industrial production include "mater Bi" of Montedison company in Italy and "no von" of Warner Lambert company in the United States. The former has a production capacity of 23000 T/A. the latter built a production plant with an annual output of 45000 tons in 1992. Its products include extruded sheets, blow molded films, flow cast films, injection molded products, hollow containers and toys. Its disadvantages are hydrophilicity and high price (3.56 ~ 6.67 $/kg)

the starch plastic developed and produced by Jiangxi Academy of Sciences and Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, has a starch content of 60%, but it cannot be widely popularized in the current plastic industry due to the tape casting method; Jiangxi Academy of Sciences also introduced starch foam material, which has similar performance and price to polystyrene material, and can be used as heat preservation and shockproof materials

the starch content of all starch thermoplastic is more than 90%, and the other components added are also degradable. Its manufacturing principle is to disorder starch molecules to form thermoplastic starch with thermoplastic properties. Traditional plastic processing methods, such as extrusion, injection molding, calendering and blow molding, can be used for its molding. The moisture content of traditional plastics should be controlled at almost anhydrous level during processing, while full starch plastics should have a certain amount of moisture during processing, and the temperature should not be too high to avoid charring

in the early 1990s, feiruzzi company in Italy announced that it had successfully studied "thermoplastic starch", which can be set up with general plastics (2) environmental protection issues that the public mainly pays attention to in the process of project construction and operation; It can be used to produce agricultural film, feed bag and fertilizer bag. After use, the bag can be granulated and used as feed. German and American companies have also developed thermoplastic starch plastics

China began to study all starch thermoplastics in the early 1990s. Zhejiang University, Jiangxi Academy of Sciences and Tianjin University used a variety of processes to make starch disordered. With the support of the National Natural Science Foundation of China, Jiangxi Academy of Sciences has developed a full starch thermoplastic film. Its performance can meet the national standard for similar applied plastic films, and it is completely degraded without leaving traces after 3 months. After testing, its degradation products are mainly CO2 and H2O

3.2 carbon dioxide resin biodegradable material

carbon dioxide is a weak acidic oxide, which can react in the presence of alkaline compounds. In addition, carbon dioxide is also a strong ligand, which has the ability to form various complexes with metals (the complexation may be reversible), because the electron transfer to metals can occur in one or more of carbon dioxide or oxygen atoms. Carbon dioxide in the complex may exist in a straight or curved form, and there are four forms of binding with a metal atom, Fig. 1; The combination with two metal atoms has more possible forms

there are many opportunities for carbon dioxide with these characteristics to be activated and participate in some reactions, in which CO2 is inserted into the chemical bond composed of metal, carbon, silicon, hydrogen, nitrogen, phosphorus, halogen, etc. The insertion can be carried out in a "normal" manner. That is, the carbon of CO2 is connected with the electron rich end of the insertion bond. The mechanism of anionic coordination copolymerization of CO2 and many monomers is that CO2 and its comonomers are complexed with catalyst metals in turn. This insertion reaction is also the basis for the preparation of various carboxylic acids or carboxylates, carbamates, organosilicon, and organophosphorus compounds

the activation of carbon dioxide is affected by the surrounding complex environment. Some metals (such as copper, zinc, cadmium, iron, cobalt, tin, aluminum, etc.) and many ligands (such as carboxyl, ether, ester, amine, phosphorus and other oxygen, nitrogen, phosphorus containing groups) may form effective active centers. In many cases, the use of a variety of ligands, especially macromolecular ligands, may produce good synergy to activate carbon dioxide to a higher degree

Inoue Xiangping found that carbon dioxide can be polymerized with epoxide to form aliphatic polycarbonate (APC), which is the most promising carbon dioxide copolymer so far:

Nishida harno used the clear zone method to determine the biological degradation ability of APC in different environments, and found that under specific environments, microorganisms can degrade (1,3-oxbridge-2-ketone). Inoue Xiangping implanted the copolymer (PEC) of carbon dioxide and ethylene oxide (EO) into animals, and it was found that it gradually disappeared after a week; Fang Xinggao's experiment shows that the terpolymer of PEC, carbon dioxide propylene oxide (P0) - succinic anhydride (SA) and carbon dioxide propylene oxide caprolactone (CL) can be well compatible with organisms, which can be regarded by microorganisms as their firm task and mission solution to revitalize the modernization of the ruling party of China and reform

the degree of biodegradability (expressed in loss WPA per unit surface area) can be controlled by copolymerization ratio. Samples containing more EO, SA, CL units have higher biodegradability; At the same time, samples with small molecular weight degrade faster. Degradation is considered to be carried out on the surface of the sample because microorganisms cannot penetrate into the sample like water, but only act on the surface. During degradation, the molecular weight and unit components of the residual sample (after cleaning) are basically unchanged, which confirms the above view. Wrinkle Xinwei et al. Prepared the above copolymer by adjusting polymerization, so that it has 2 or 3 terminal hydroxyl groups and has a relative molecular weight of 2000 ~ 5000 according to the design, and then made it into polyurethane. While maintaining a certain biodegradability to avoid virus infection, they obtained mechanical properties that can meet the use requirements

Takanashi et al. Used the terpolymer of carbon dioxide, propylene oxide and epoxide containing ester bond as drug sustained-release agent. Masahiro et al. Prepared PPC microspheres by evaporating solvent as the carrier of drug release system, and studied the factors affecting the drug release rate of the system, such as the molecular weight of PPC, drug content, etc. The results showed that the drug release rate increased with the decrease of the diameter of the microspheres or the increase of the loaded drug concentration, but the drug release rate and biodegradability had nothing to do with the molecular weight of the copolymer. Through SEM observation of the morphology of the microspheres before and after drug release, it was confirmed that PPC microspheres supported the long-term and uniform release of drugs

3.3 medical biodegradable materials

with the development of science and technology, the research of life science has attracted more and more attention. Biomedicine, which is related to human health, plays a very important role in life science. Biomaterials is the latest branch of biomedical science. It is a frontier discipline formed by the intersection of biology, medicine, chemistry and material science

the "biomaterial" specially defined by the French conference of the international organization for Standardization (ISO) is biomedical material, which refers to "inanimate material used for medical purposes to contact with tissues to form functions"

3.3.1 aliphatic polyester

lactones (including lactides), such as caprolactone, glycolide, lactide, etc. through ring opening polymerization, a class of aliphatic polyester with excellent biocompatibility and biodegradability can be obtained. They have been widely used in various fields of biomedicine and environment-friendly materials. In addition, another kind of biodegradable aliphatic polyester can also be obtained by biological fermentation, such as poly-3-carboxylbutyrate, poly-3-carboxylbutyrate copolymer, etc. They have unique physical properties. In addition to being applied in biomedical field, they are also expected to be applied in microelectronic industry. Although there are few reports on the ring opening polymerization of lactones, a lot of research work has been carried out around its synthesis process and the selection of efficient catalysts, which can be summarized as follows:

(1) protonic acid catalysts

(2) halide catalyst

(3) anionic catalyst

(4) organoaluminum compound catalyst

(5) tin salt catalyst

(6) rare earth compound catalyst

(7) active polymerization catalyst

3.3.2 polylactic acid and its copolymer

lactone ring opening homopolymers (such as PLA, PCL, PGA, etc.) are hydrophobic substances, and the degradation cycle is difficult to control. Copolymerization with other monomers can change the hydrophilicity hydrophobicity and crystallinity of materials. The degradation rate of polymers can be controlled according to the molecular weight of copolymers, the types and proportions of comonomers. Copolymers with specific structures (such as diblock, multiblock, star structure, etc.) can combine the characteristics of different materials and give special properties, Therefore, the synthesis of PLA copolymers with different compositions and specific structures has become a research hotspot in recent years. Some of these materials are good carriers for cell culture and tissue engineering, and some can form specific capsule structures, which can be used as drug carriers

3.3.3 polycaprolactone and its copolymer

polycaprolactone is a partially crystalline polymer, which has good permeability and excellent compatibility with other polymers, so it has been widely used in the industrial field. However, due to its poor biocompatibility, it can only be degraded under enzyme catalysis, which limits its application in biomedical field. In order to overcome this shortcoming, people try to synthesize various block copolymers of caprolactone by random copolymerization to improve its biodegradability. Feng Xinde and others used the catalyst of tessvie to synthesize polycaprolactone polylactic acid diblock copolymer and polycaprolactone polylactic acid polycaprolactone triblock copolymer. The results show that this copolymerization has the characteristics of active polymerization, and its biodegradability can be adjusted by the change of copolymerization composition; Jing Yabin synthesized polycaprolactone polylactic acid copolymer with yttrium trifluoroacetate and triisobutyl aluminum composite catalyst, and studied its biomedical properties; Wang Shengguo studied polycaprolactone

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