Application of Biodegradable Polymers in Cushion Packaging Materials (in)

(2) Starch blended with other natural polymers

Starch itself has weak melt strength and is prone to absorb water, and can not meet the foaming requirements. Therefore, it needs to be blended with other biodegradable polymers to toughen and strengthen the starch to meet the requirements for preparing foamed materials. Other biodegradable polymers mainly include plant fibers, chitosan, and the like.

Andesen and others invented the preparation process of fiber reinforced foam. GM Glenn et al. studied the effect of CaCO3 and fiber on the physical properties of the product when the starch foaming cushioning material was prepared by baking. The results show that the foamed cushioning material prepared from pure starch has lower fracture flexing force and smaller elongation at break than polystyrene foam; CaCO3 can not improve the mechanical properties of the foaming cushioning material, but makes the density The pure starch foam cushioning material is large; the addition of fiber to pure starch reduces the density of the product and significantly increases the flexural force at break. When the ratio of starch to fiber is approximately 5:1, the flexural force at break is higher than that of pure starch. %, the elongation at break increases by twice. The research of RL Shogren et al. [12] showed that adding 5 to 10% of fiber in starch can produce higher strength foaming cushioning materials, especially when the humidity is higher and the temperature is lower; the electron microscope analysis shows that: Bonding with fiber matrix is ​​good, it plays a reinforcing role. When the humidity reduces the starch to become more brittle, the fiber can act as a “bridge” to connect the fracture surfaces; when the humidity is high, the amorphous foam structure begins to change. It is soft, and the fiber network structure increases the strength of the article, which may be due to the increase in viscosity and resistance to swelling due to the addition of fibers.

The PSP company in Bremen, Germany, has developed materials from old newspapers, waste paper and flour as substitutes for foams. The main ingredients of the raw materials are plant fibers and starch. The process first cuts the old newspapers that have been recovered into shreds, then disperses them into fibrous pulp, mixes them with flour in a ratio of 2:1, and mixes the pulp into the extruder to form cylindrical pellets to form foam paper. Using foam paper pellets as raw materials, different types of packaging materials can be produced according to different needs. The foam paper can be molded once, without chemical additives, and can be recycled and reprocessed after use.

Dai Hongmin et al. conducted research on the foaming process of fiber and starch-based cushioning materials. The main materials are waste paper and cardboard, corn starch and fillers, and the ratio of the three is controlled around 4:4:2. The more corn starch, the more easily the product expands and foams, and the higher the foaming magnification. Waste paper and paperboard are crushed and ground into velvet, mixed with cornstarch, filler, water and other auxiliary foaming agents, moisture-proof agent, release agent, etc., and mixed to form a mixture and then made into a diameter of 1~3mm. The particles are then fed into an extrusion apparatus to make a pelletized foamed pulp. The foamed pulp pellets are then used as a raw material to be fed into a dedicated metal mold and heated in a metal mold to produce differently shaped packaging materials as required. . The main raw materials for paper and paperboard are plant fibers, which are as hygroscopic as starch, prone to mildew in wet environments and cause qualitative changes, and are used as buffer packaging materials to easily cause corrosion of electronic, instrumentation, hardware, etc. contents of content, thus solving Moisture resistance is a key technology in this process. A VAE copolymer emulsion has a good effect after dilution and is modified to meet the requirement of non-toxicity, high temperature resistance and waterproof penetration, and can be self-degraded under certain conditions. In order to make the VAE moisture-proof agent evenly dispersed in the material and improve the moisture-proof performance, it is necessary to add the moisture-proof agent and agitate it twice when the plant fiber is stirred and the starch is stirred respectively. The total amount of the two added is about the plant fiber, the starch and the filler. About 5% of the total.

Hosokawa et al. reported the preparation of biodegradable packaging materials by blending mechanically crushed fine starch granules with a chitosan solution. The mixture of starch and chitosan solution is heated and gelatinized or pre-gelatinized starch is mixed with chitosan acetic acid solution to prepare a high-concentration raw material. The moisture content of the raw material is controlled below 60%. It is foamed by steam, expanded and then heat-pressed. Made of foamed products, used as a container for fresh food. The product has high strength, good foaming performance, easy to be completely degraded, and the degradation product is harmless to the environment. It will not produce harmful gas when it is burned, and it is expected to replace the use of polystyrene foam in various aspects.

(3) Starch and synthetic polymer blends

Randa I. L. et al. studied the process of preparing foams from starch/PVA blends. The results showed that at lower humidity, 88% alcoholysis of PVA increased the strength, while at higher humidity, 98 The alcoholysis of PVA increases the strength greatly; the bending strength increases with the increase of the molecular weight of PVA; the addition of salts such as Ca, Zr, etc. can further increase the water resistance; microstructure analysis reveals that the expanded starch The particles are embedded in the PVA, the starch gels during baking, and the PVA transitions to a higher degree of crystallization. A study by RL Shgren et al. [12] found that the addition of PVA increased the strength and bending properties of foams made from corn starch and improved the water resistance.

American Werber-Lambert Company developed a product called “NOVON”, which uses gelatinized starch as the main raw material, water as plasticizer, and fully biodegradable polyvinyl alcohol, which can be used with common plastic molding processing technology. Forming, but also according to the need to add different additives to improve flexibility, dimensional stability and high temperature performance. The content of starch in the material can reach more than 90%. It can be biodegraded under aerobic and anaerobic conditions. The decomposition rate reaches 100%, and it has good mechanical properties, and its strength can reach the same level of polystyrene. Currently, it is widely used in commercial applications and has many varieties, including foam cushioning materials.

JY Cha et al. studied the effects of extrusion temperature and raw material moisture content on the physical properties of starch-based foams. The components were 49% wheat or corn starch, 33% EVOH, 10.5% water, 7% foaming agent and 0.5% Nucleating agent, extruded from a single screw, with a screw speed of 100 rmh. The results show that the bulk density decreases with increasing extrusion temperature, the maximum expansion occurs at 140°C, and the density is 4 to 8 times that of polystyrene.
(to be continued)