Study on Properties of Starch and Fiber Molded Degradable Packaging Materials

2.2 Effect of Plasticizers on Mechanical Properties of Sheets

Due to the large molecular weight and the strong affinity between molecules, starch is not only difficult to process but also has a relatively brittle material. Some small-molecule polyols can be used as plasticizers to reduce the interaction between starch molecules, so that the material has better flexibility and elasticity, and is easy to process and shape "7". Small molecule polyols can penetrate between the starch granules during the mixing process of the material system, destroy its internal hydrogen bonds, reduce the intermolecular force between the starch molecules, and make the segments easy to slide. Several small-molecule polyols were selected as plasticizers in the experiment. Under the same content (20 parts), the tensile strength and elongation of the material were tested. The results are shown in Figures 3 and 4.

The molecular weight of ethylene glycol, 1,2-propylene glycol, and glycerol is higher than the molecular weight of pentaerythritol and sorbitol, the molecules are easy to move, and the mixing process is more effective in infiltrating the molecular chain of starch through the hydroxyl group to hydrogen. The bond method is combined with starch to form a relatively firm uniform system, thereby softening macromolecules and improving flexibility. Therefore, they have a greater ability to disrupt intermolecular forces of starch, which is characterized by greater elongation at break, as shown in Figure 3. . Among them, the number of 1,2-propylene glycol single molecule hydroxyls is less than glycerol, and the destructive power of hydrogen bonds between starch molecules is small, so the elongation at break is also lower than that of glycerol." On the other hand, pentaerythritol and sorbitol alone The molecules contain more hydroxyl groups and have stronger interactions with starch molecules. However, their penetrability is far lower than that of ethylene glycol, propylene, and triol, and their destructive force is small, so that the material has small elongation at break and high tensile strength. As shown in Figure 4.

During the molding process, ethylene glycol, 1,2-propanediol, and glycerin are liquid at room temperature and have strong fluidity, and the mixing of the materials facilitates uniform dispersion of the components. Pentaerythritol and sorbitol have large molecular weights and are solid at room temperature. The mixing of materials is relatively difficult, and the brittleness of the formed material is too large and there is a phenomenon of warpage. As a result, the plasticizer of the system is poor. In comparison, ethylene glycol and glycerin have better plasticizing effect.


2.3 Influence of Inorganic Fillers on Mechanical Properties of Materials

In this experiment, talcum powder was used as the inorganic filler of the material. The chemical properties of talc powder are inactive, chemical resistance and electrical insulation, and can improve the dimensional stability, rigidity and hardness of the material. In addition, the water resistance of the material can also be improved. Appearance whiteness. The effect of talc content on the mechanical properties of the sheet is shown in Figures 5 and 6.

As the content of talc increases, the stiffness of the material gradually increases, as shown in Figure 5. Talc as a rigid filler has the effect of increasing rigidity and stiffness and reducing warpage. The talcum powder (800 mesh) particles used in the experiment are fine, which is conducive to the uniform dispersion in the material system. With the increase of the content, the viscosity of the material system is gradually reduced, and the adhesion to the equipment during molding is reduced, thus facilitating processing. operating. However, the increase of talc content, as an inert filler, dispersed in the system affect the combination of starch, PvA and fiber, so that the strength of the system decreased, so the tensile strength of the material and the elongation at break have a slow decline. As shown in Figure 6. Therefore, according to the specific requirements of materials, comprehensive consideration of various mechanical properties to determine the amount of talcum powder.

3 Conclusion

Starch has a great influence on the mechanical properties of the sheet. With the increase of the content, the tensile strength and stiffness of the sheet gradually increase. After a certain degree, the sheet begins to decrease. The elongation at break of the sheet decreases continuously. The amount should be reasonably controlled according to the specific material requirements. Small-molecule polyols can be used as plasticizers for sheets, among which ethylene glycol and glycerol have good plasticizing effect, which facilitates penetration into the starch molecular chain, reduces intermolecular forces, and softens macromolecules in the mixing system. Make the material have better flexibility. Talc powder can be used as inorganic filler of materials. With the increase of talcum powder content, the viscosity of the blending system decreases, and the stiffness of the sheet increases, but the tensile strength and elongation at break decrease. The amount of talcum powder should be adjusted according to the specific requirements of the material.

(Wen/Wang Liyuan Wang Jianqing Tianjin University of Science and Technology)
"Packaging Project"