(4) Starch as a component of ordinary foam
A lot of research has been done on starch-filled polystyrene foams. The manufacturing method is that the starch granules and the foam granules are mechanically mixed and then foamed. However, such filled foams have some defects in production and performance. The biggest problem is that the flow rate of the foam is always maintained at more than 30% during the manufacturing process, and the starch that has been filled will gradually carbonize during the process of reuse, making the final product darker or even discolored, affecting the appearance and sales. To make the color change is not obvious, you can only reduce the amount of starch filling or discard the return material. The former will greatly reduce the degradation effect, while the latter will cause waste and additional pollution. In addition, the thoroughness of degradation is still controversial. It is generally believed that only starch is swallowed by microorganisms, and the framework of polystyrene is still left behind.
There are many potential functional groups on the starch segments, and they can all be reactive in certain conditions. According to this characteristic, the polycondensation reaction can be used to make the starch part of the polymer. At present, there are many researches and reports on starch-based polyurethane foams. Roberta Alfani et al. synthesized polyurethane foams with soluble starch, PCLt, and hexane diisocyanate. The experimental results show that the addition of starch will slightly reduce the reaction rate, but can be added to the catalyst such as dibutyltin dilaurate to adjust the reaction rate, in order to obtain the best results. The foams made are mostly open-celled, and the glass transition temperature increases with the increase in the amount of starch. The thermogravimetric analysis of the starch-based polyurethane foam with the same starch content and the polyurethane foam incorporated into the starch after the reaction showed that the two are quite different. These differences confirm that the starch participates in the composition of the polyurethane foam in a bonding manner.
Cunningham et al. used a raw material called Fantek as a starch source. Fantesk is a starch-oil mixture made by the jet method. They mixed and reacted a certain amount of Fantels, polyester polyols, aromatic polyisocyanates with dibutyl tin dilaurate and water. Analysis of the test products by FTIR revealed that the ratio of unreacted isocyanate/phenyl peak (2277/1600) remained essentially constant in different starch/polyester systems, and the phenyl peak was only related to the amount of aromatic polyisocyanate added. While the relative excess of isocyanate. This shows that starches are involved in the reaction as polyester polyols. An increase in the amount of starch will increase the hardness of the foam, which is related to the viscosity of the reaction mixture and tearing of the network structure during expansion.
2. Problems that exist
(1) Performance The types of biodegradable foams studied at home and abroad are many, many of which can be compared with traditional plastics of the same type in terms of mechanical properties, but their performance is often unsatisfactory. The main disadvantage is that the foamed products containing starch or fibers have poor water resistance, poor wet strength, and a serious drop in mechanical properties upon encountering water, and water resistance is precisely the advantage of traditional foams in use. The biodegradability of the degradable foam material will inevitably impair the durability of the product, to a certain extent, reducing its mechanical properties, thereby limiting the scope of application. In addition, starch-based degradation materials are prone to starch recrystallization during use, making the material slowly brittle, reducing flexibility, affecting performance.
(2) Degradability Starch-filled foams prepared from ordinary foams can be decomposed by microorganisms in the natural environment, but the materials are only partially weightless, and the ordinary plastics contained in them are difficult to degrade and remain in the soil. Over time, pollution is caused, so these products should be eliminated. For biodegradable foamed materials mainly composed of starch, fiber and other synthetic polymers, the degradation rate is not easy to control, and the addition of organic additives in some materials may affect the final degradation of the material.
(3) Prices It is widely believed at home and abroad that the price of biodegradable foam products is more than 50% higher than that of current foams of the same type, of which the total degradability is 4 to 8 times higher than that of conventional foams. There is no market competitiveness, and promotion is more difficult.
3. Development prospects
The application of biodegradable polymers such as starch and fiber in degradable materials has great advantages and potentials. Starch raw materials, in particular, are abundant in source and cheap in price. Foreign countries, such as the United States, have huge inventories for many years. In recent years, China has also massively pressed warehouses, and it is in urgent need of exploitation and utilization. At the same time, it also needs to increase its added value to promote agricultural production. Natural fiber raw materials are rich organic materials in the natural world, and many varieties are inexpensive. The two major advantages of rich and cheap raw materials and complete biodegradability are the material basis and prerequisite for the development and utilization of biodegradable materials.
The potential market for biodegradable materials is enormous. With the enhancement of environmental awareness and the improvement of environmental protection regulations, the market for degradable materials will rapidly expand, especially in the packaging fields such as films, sheets and cushioning materials. In recent years, the electronic information industry has developed rapidly. Mobile communications, notebook computers, new color TVs, information appliances, and automotive electronics are forming hot product markets. The electronic information industry has grown in size and the sales volume of its products has soared. As a result, the number of boxes, cushions, and trays required has grown rapidly. International laws and regulations have been published, and higher environmental protection requirements have been put forward for electronic and electrical products, mainly for raw materials, accessories and packaging. Therefore, the completely degradable packaging material replacing the traditional plastic is the trend of the world's green environmental protection and meets the strategic requirements for sustainable development. At the same time, it also brings tremendous impetus to the application of biodegradable polymers in packaging materials.
For starch, fiber and other biodegradable polymers, the main task of future application research is how to improve the material strength, water resistance, and degradation controllability through molecular design, blend modification and other means. In addition, the development of formulation design, process design, biological inducers, degradation control agents, etc. is also an important research topic. Continuously improving and improving the performance and degradation performance of biodegradable materials and reducing production costs are the leading directions in the research field. It is believed that biodegradable polymers will have broader application prospects in the degradation of packaging materials, and will make greater contribution to green packaging.
Wang Liyuan, Wang Jianqing, School of Packaging and Printing Engineering, Tianjin University of Science and Technology Information Source: China Packaging 2005/2