Study on the Properties of Starch and Fiber Molded Degradable Packaging Materials

At present, the annual output of plastics in the world exceeds 100 million tons, and China's annual consumption exceeds 6 million tons, of which 25% is used for packaging. Plastics are light and bulky, and waste disposal is difficult. Landfills and incineration are not ideal solutions. “White pollution” has become a global problem. People are looking for completely degradable materials that can replace traditional plastics through various means. Starch is a natural polymer, rich in raw materials and cheap in price. It is decomposed into glucose under the action of microorganisms, and is eventually metabolized into water and carbon dioxide. It is an inexhaustible renewable resource." Starch and other natural polymers such as cellulose, hemicellulose, lignin, chitin, etc., produce completely biodegradable materials. It is a kind of all-natural biodegradable material that has developed rapidly in recent years. Its membranes and sheets Can be used as a variety of packaging materials, can also be processed into a variety of products, the application of a broad prospect [2].

In order to explore the production technology and packaging suitability of this new type of biodegradable packaging material, in recent years we have used starch and plant fibers as the main raw materials, adding appropriate amounts of cross-linking agents and reinforcing agents, made a mixture and molded it, and followed Related standards test its performance. The results showed that the material made of starch and plant fiber as the main raw material has good mechanical strength and biodegradability, and has certain development and application value.

1 Experimental materials and methods

1.1 Materials and Equipment

1.1.1 Materials

Potato starch (Tianjin Dingfeng Starch Development Co., Ltd.); Softwood bleached kraft pulp (Chile 'Venus' brand); Polyvinyl alcohol 1788, Talc (800 mesh) (Tianjin Loctite Chemical Co., Ltd.); Glycerin, B Diol, 1,2-propanediol, sorbitol, pentaerythritol (Tianjin Chemical Reagent Sixth Factory).

1.1.2 Equipment

XLB-DC electromagnetic plate vulcanizing machine (Zhuzhou Times Electromechanical Equipment Co., Ltd.); electric constant temperature water bath (Shandong Weir science equipment Co., Ltd.).

1.2 Experimental methods

The starch was gelatinized and mixed with the polyvinyl alcohol solution, mixed with plant fibers, plasticizers, inorganic fillers, cross-linking agents, and the rest of the starch, and then placed into a mold and molded into 1.6 mm thick sheets. Molding temperature is 130 ~ C, pressure 15MPa.

After the sheet is formed, it is treated in the standard atmospheric environment for about 48 hours. The mechanical properties of the material are tested according to GB 453-79 for tensile strength and elongation. The stiffness test is performed according to GB 2679.3-81; the degradation performance is based on soil-buried organisms. Degradation experiment "3": Weigh the sample from the dry to constant weight, mark it as buried on the surface 10cm below the ground surface, remove it after every period of time, wash it, dry it and weigh it, and calculate the weight loss rate.

2 Results and Discussion

2.1 Effect of Starch Content on Mechanical Properties of Sheets

Starch content is a major contributing factor to the mechanical properties of the material. In the molding process, starch and polyvinyl alcohol (PVA) are used in combination to synergize the polar material system. "4". PVA is used as an aqueous solution to provide a macromolecular skeleton in the material. The gelatinized starch particles are embedded in the material. In the PVA molecular chain, it binds tightly to make the material have a certain mechanical strength. The mechanical properties of the prepared samples were tested. The changes of the mechanical properties of the materials with the starch content are shown in Figures 1 and 2.

As shown in Figures 1 and 2, as the starch content increases, the tensile strength and stiffness of the material increase gradually. The starch granules are gelatinized and embedded between the PVA macromolecular segments and are tightly bound thereto, so that the material has a certain mechanical strength. When the starch content is continuously increased, the synergistic effect produced by PVA increases, the adhesion to fibers and other raw materials is better, the bonding is tighter, the viscosity and hardness of the system gradually increase, and the stiffness and tensile strength of the material are both increased. It is gradually increasing. However, when the content is high to a certain value (about 60 or so), the change in the material strength is small, slightly increasing, and the tensile strength gradually decreases. This is because starch and PVA combine to a certain extent, the starch molecules are easy to entangle, forming a cluster structure "5", spatially far away from the PVA macromolecular chain, affecting the strength of the material. On the other hand, with the increase of starch content, the elongation at break of the material has been gradually decreasing. This is because the macromolecular framework provided by PVA in the material is the most important factor affecting the toughness and elasticity of the material. The content of PVA gradually decreases, and the material gradually becomes brittle, which makes it easy to break.

In addition, in the material forming process, the excessive use of starch will make the system too high in viscosity and hardness, hindering the dispersion of plant fibers (especially long fibers), affecting the homogeneity of the material and easily causing local defects. At the same time, the system's high viscosity has a strong adhesion to the equipment, increasing the difficulty of practical operation "6". Therefore, considering the mechanical properties and processing performance, the amount of starch should be controlled within a certain range.

(to be continued)