On Green Packaging Materials (2)

1.2.2 cellulose-based biodegradable plastics

Natural polymer cellulose, like starch, is a non-thermoplastic material and cannot be processed by conventional processing methods. Its application must also be modified to destroy the hydrogen bonds of cellulose and react the hydroxyl groups on cellulose molecules to give cellulose. The derivatives are then blended with some synthetic resins and processed into various products or membranes with good mechanical properties, low production costs, and high degradation rates for packaging of food and daily necessities. The Shikoku Technology Laboratory of Japan will stir the fine cellulose, chitosan acetic acid aqueous solution, plasticizer, etc. and stir it to dry on the glass plate. The airtightness is 10 to 100 times that of PE. The strength is 10 times that of PE and the tear strength is similar to that of cellophane. These materials are fully biodegradable and have good air permeability. However, they are non-thermoplastic materials and are not easily processed by blow molding methods. The properties need to be improved and their applications need to be developed. The disposable cutlery made of rice husk as raw material developed by Shantou Luheng Industrial Co., Ltd. has initially possessed industrial-scale production capacity, and its disposable packaging containers, especially food packaging equipment for supermarkets, have been tested in Japan and the United States. Ground.

1.3 Light and Bio Double Degradable Plastics

In biodegradable plastics, the degradation behavior of the material must be performed in a biologically active environmental medium. Adding a proper amount of photosensitizer can make the plastic have both photo and biological degradation properties. Under certain conditions, the controllability of degradation rate is obviously improved. Therefore, the development of photo-biodegradable plastics has attracted widespread attention at home and abroad and has become one of the important research and development directions for degradable plastics. Such materials not only overcome the defect that the photodegradation is not sufficiently degraded when there is no light or insufficient light, but also overcome the defects that the biodegradable plastics have complicated processes and high costs, and thus are the most ideal plastics. Most of these materials are used to produce agricultural mulch, but applications in packaging have also been reported. For example, the production technology of light and biodegradable polypropylene fast food boxes developed by Fuzhou Xingchuang Light Industry Machinery Technology Development Co., Ltd. has passed the appraisal of the National Plastic Testing Center. This kind of lunch box has a low production cost and is a better one among the five kinds of disposable tableware currently meeting the national technical standards.

Biodegradable plastic is a member of the plastic family. Its appearance not only expands the function of plastics, but also alleviates environmental contradictions to some extent. The use of natural polymer materials and their derivatives and degradable plastics for blending or compounding to produce biodegradable and optically and biologically degradable plastics will become an important development direction for disposable plastic packaging materials. With the depletion of petroleum resources in the world today, the development of non-petroleum-based degradable plastics has extremely broad prospects for development and has now become a hot spot in world research and development.

However, in the packaging field, its products are still difficult to compete with traditional general-purpose resins, and the application field is still very limited. In the application process, there are still some problems: if the price of biodegradable plastics is 2-15 times higher than that of ordinary plastics, it is more difficult to popularize and apply; more food is consumed and visual pollution cannot be eliminated in time; degradation of some degradable materials The process knows very little, and its degradation control problem has not yet been well resolved. As a result, it is difficult to formulate a unified degradation assessment system. The research, development, and application of biodegradable materials are greatly constrained.

2. Natural biomolecular materials

Natural biomolecule materials refer to packaging materials that are made from natural biomolecules as the main raw material, supplemented with necessary auxiliary materials, and produced through a certain production process. Natural biomolecules such as cellulose, starch, chitin, and protein are abundant in natural resources. After the used natural polymers are discarded, they can be completely decomposed naturally and completely non-toxic in the natural world. Therefore, such natural polymer materials are increasingly subject to Pay attention.

2.1 Natural Plant Fiber Packaging Materials

Natural plant fibers such as bagasse, cotton stalks, husks, corn stalks, rice straw, wheat straw, etc., are a kind of renewable natural resources rich in resources. According to the survey, China's annual crop straw is more than 500 million tons. Plant straws have many advantages as packaging materials, such as good buffering performance, non-toxic, odorless, good ventilation performance, and completely natural degradation after use. Paper materials are people's most familiar and widely used green packaging materials. They have a wide range of raw materials. Waste can be used to recycle recycled paper and is easily corrupted in the natural environment. It is the earliest application of green packaging materials. In the 1990s, people in the materials industry proposed "to use paper to mold." Typical varieties currently widely used for packaging are pulp molding and honeycomb paperboard products. In particular, molded pulp products are used to replace refractory plastics and are widely used in tableware, poultry egg trays, fruit trays, industrial trays, food and semi-finished packaging, and medical device packaging. Northwest Agricultural University of China has conducted a lot of research in this area, researching and developing fruit and vegetable packaging linings, poultry egg trays, supermarket trays, corrugated paper, disposable tableware and other products. Its production process has matured and will soon be brought to market in large quantities.

Although paper has many advantages, there are also many shortcomings: papermaking consumes a lot of wood and causes water pollution at the same time; papermaking costs are high, and the mechanical strength and water resistance of paper are also difficult to compare with plastics. This shows that green packaging materials also have the characteristics of the times. Only in the processing of fiber products, the use of fiber products will be more extensive, and its enormous potential can be used to its due.

According to relevant research, straw-like plants (including slag, shells, and cakes) are used as raw materials, and biodegradable and protein denatured technologies are used to produce fiber degradable packaging materials. This technology has the characteristics of waste recycling, clean production, non-hazardous products, and can be used as feed and fertilizer after being discarded. Its main production process is: First of all, the "biological bacteria" technology is used to biologically treat the straw (after a series of chemical, physical and biological changes), and some substances such as cellulose and protein precipitate out of the treated straw. , fats, nitrogen-free extracts, and some substances still remain as they are, such as semi-fibers, lignin, and insoluble salts. This processed material is called “biomass” and adjusts the structural state of raw materials for further processing. The second step is to use “protein denaturation” technology, which means that under the influence of external factors, the natural protein molecules disintegrate their spatial structure and change from an ordered configuration into a disorderly disordered and loosely stretched peptide chain, resulting in protein Changes in the physical and chemical properties of the molecule. After the above two-step technical treatment, the nature of the raw materials has undergone fundamental changes, the processing of the raw materials has been completed, and the raw materials have been subjected to mechanical processing and shaping, and the desired fiber packaging material can be made.

Recently, Xi'an University of Architecture and Technology applied the natural plant cellulose material such as straw and rice straw as main materials, together with safe and non-toxic substances, and developed a completely degradable buffer packaging material. The product is small in size, light in weight, high in compression temperature, and has a certain degree of flexibility. The cost is comparable to that of foamed plastics. It is lower than paper and wood products and can be fully decomposed into organic fertilizer in one month in nature. Yintai Company of Jilin Province has also developed a new non-polluting plant cellulose packaging material with straw as its main raw material, which can be quickly decomposed after use.