Analysis of Biodegradable Packaging Materials and Its Development

The progress and achievements made by the chemical industry since the second half of the 19th century are largely due to the use of mineral raw materials as the basis for synthesis. Synthetic dyes prepared from coal have replaced natural dyes, and this light-stable colorant has for the first time entered the lives of the general public. Nowadays, mineral raw materials represented by oil and gas are the most important raw materials for the chemical industry, exceeding 90%, ranking second only to energy and transportation. According to the statistics of OECD member countries, energy accounts for 54%, transportation accounts for 35%, and the chemical industry accounts for 12% (half each for raw materials and processing). In the chemical industry, oil and gas resources used as raw materials are mainly converted into polymers.

Over the past 50 years, General Plastics has achieved tremendous success, providing a reliable raw material base and a variety of applicable properties. By melting, a large number of items (such as films and moldings) can be manufactured. The processing method is not only inexpensive but also environmentally friendly. Very small. After the energy crisis of 1973, alternative energy sources and resources, such as biomass problems, attracted attention and strengthened research. With the drop of crude oil prices, public interest in it has declined again. However, in terms of geopolitics and economic development, over-reliance on oil and its limited availability make people think about alternative energy sources and resources. According to the proved oil reserves, using modern mining technology, it can only be adopted for 40 years. This forecast is more optimistic. This is based on the continuous increase of crude oil reserves in the Middle East. Now that the greenhouse gas CO2 is completely generated from mineral raw materials, this has become the unpredictable and irreversible cause of global climate change. Traditional plastic waste is buried underground because degradation is slow and will occupy valuable land for a long time. Therefore, it is envisaged that recycling applications based on renewable resources will be very attractive, especially for applications. Natural products.

The biodegradable materials that people research and develop nowadays are mostly based on natural products, some are polyesters synthesized by microorganisms, and some are made from renewable resources and then polymerized into materials such as polylactic acid (PLA). In fact, some Monomers can also be prepared using petrochemical routes. Therefore, the biodegradability of research materials should include both renewable resource base materials and petrochemical base materials, and their ecological potential should be compared.

1. About biodegradability

Biodegradable materials are now receiving attention. Biodegradability and preparation from renewable resources are two different concepts. Naturally occurring polymers, such as cellulose or natural rubber, are biodegradable, but biodegradability is related to the chemical structure of the material, regardless of whether the structure is made from renewable resources or mineral resources. Germany has a biodegradability clause in the 1998 standard test method as a measure of the decomposability of plastics. In the analysis, in addition to the chemical composition (such as the presence of a certain heavy metal), it is also necessary to test the possibility of complete degradation under laboratory conditions, to test the degradation and decomposition properties under actual living conditions, and to determine the decomposition of the large bird, Earthworms and other ecotoxicities. The definition for biodegradability is: Under laboratory conditions, 60% of the organic carbon must be completely converted within 6 months. In actual conditions, 90% of the plastic should be able to degrade into fragments smaller than 2mm. In addition to natural polymers, biodegradable polyesters prepared by microorganisms or chemical methods have also become the center of attention. Degradation generally occurs in two steps: First, it is enzymatically or chemically hydrolyzed into low-molecular-weight fragments, and sometimes it can be decomposed into original monomers, which can be reabsorbed by cells and eventually become CO2 and water. The amorphous regions in the polymer erode much faster than the crystalline regions. The crystallinity and grain size of the polymer have a great influence on the degradation rate. Traditional polyesters and polyamines have a high degree of crystallinity, and this structure plays a decisive role in their main mechanical properties. Therefore, molded parts and fibers can be made. However, it has resulted in a hard-to-degrade condition that has remained stable over the useful life and under the influence of the environment.

2. About Natural Polymers

Each year, 1×10^11t of biomass is produced through photosynthesis, most of which are cellulose, starch, various polysaccharides, and lignin. Paper came out for more than 2,000 years, and now the world produces paper and cardboard 320×10^6t per year, which is higher than the annual output of petrochemical plastics 200×10^6t. However, its hydrophilic, mechanical and mechanical properties are very sensitive to water, limiting its use as a material. Soaked paper bags are useless. Moreover, unlike cellulose, which is a general-purpose plastic such as polyolefins, cellulose cannot be processed by thermoplastic methods. Therefore, cellulosic fibers (viscose fibers) or cellulose plates (celluloid) are all prepared by decomposing cellulose xanthogenate by the solution method. If they are derivatized to obtain a material suitable for thermoplastic processing, such as cellulose acetate or cellophane (cellulose nitrocellulose plasticized with rosin), but these require the further synthesis reaction with mineral resources, and the degradability of these derivatives Both are lower than unmodified cellulose. The main ingredient of pulp is cellulose, which can be used as a chemical raw material in addition to papermaking.

It is made after separating cellulose and lignin from wood. The current manufacturing process consumes a lot of energy and water, and releases pollutants (sulfides) into the environment. Therefore, the total impact of raw materials and used garbage on the environment is examined. There is no advantage for paper bags compared with polyethylene bags. . The use of inexpensive pulp and water-stable polyethylene to make composites can be used as a beverage container, which has been used in a large number in the European market under the trade name Tetrapak, which is coated with a very thin polyethylene on the wall of a container made of cardboard. Film protection layer. In post-use recycling, the pulp product can be dissolved and used as a product that does not require high fiber quality, whereas polyethylene is burned to obtain energy.

Starch and cellulose, as long as they contain a certain amount of water, can be processed by thermoplastic methods. Due to its sensitivity to water, the application of various mechanical and mechanical properties is severely limited. By blending with polyethylene or polyester thermoplastics, performance can be greatly improved. Blended with biodegradable polyester, the product can be completely decomposed. Now Noramont sells Mater-B grades in the market, about 20,000 tons per year. Some natural polymers show many active functions in living tissues, causing people to attach great importance. Obtaining natural polymers directly from natural renewable resources is a valuable shortcut for material preparation. Therefore, it is necessary to separate from the biomass, and it is necessary to solve the limitation of the application due to poor processability. Therefore, in recent years, the focus of attention has shifted to other biodegradable thermoplastics, such as microbes or chemical synthesis of various polyesters.

(to be continued)