Why do biodegradable plastic bags choose PLA and PBAT as raw materials?

material for PLA and PBAT
material for PLA and PBAT

Biodegradable plastic bags with the intensification of “white pollution” pollution, countries around the world have introduced stricter plastic restrictions, and degradable plastic bags have occupied major supermarkets and shopping malls. If you observe carefully, you will find that almost all the varieties of these degradable plastic bags are PBAT+PLA+St. So what are the advantages of PBAT+PLA+St?

01. Starch

Starch plants are widely distributed in fruits or plant fruits, roots, or leaves. There are up to hundreds of millions of tons of starch production in the world every year, which is one of many possible.

One of the renewable and biodegradable resources, it has the advantages of a wide range of sources and low prices. However, since natural starch has a microcrystalline structure and a granular structure, it does not have thermoplastic processing properties and needs to be transformed into thermoplastic starch to have thermoplastic processing properties.

Amylopectin structure

Amylose structure

02. PBAT

Polybutylene adipate/terephthalate (PBAT) is one of the degradable polyesters that has attracted much attention. It has both the good mechanical properties of PBT polyester and the good stretchability of aliphatic polyester. And ductility can also be degraded into water and carbon dioxide under natural conditions.

However, the high price of this material limits its application in the market; therefore, its cheap, degradable starch blended with PBAT is a good choice.

03. PLA

PLA is also known as polylactic acid. The production process of polylactic acid is non-polluting, and the product can be biodegraded to achieve recycling in nature. Therefore, it is an ideal green polymer material and one of the representatives of bio-based biodegradable plastics.

However, there are many deficiencies in practical applications: PLA has relatively poor toughness, lack of elasticity and flexibility, hard texture and brittleness, large solution strength, relatively low crystallization rate, etc. The above defects limit its application in many aspects.

The chemical structure of PLA contains a large number of ester bonds, resulting in poor hydrophilicity, and the degradation rate needs to be controlled. Moreover, the high price of PLA increases the cost of raw materials and limits its commercial promotion. Therefore, in view of the above shortcomings, PLA was modified.

PBAT is soft, ductile, and has a short degradation cycle; PLA is brittle, has poor toughness, and has a long degradation cycle. Therefore, mixing the two is an excellent way to improve performance synergistically.

04. Introduction of PBAT/PLA materials

【compatibility】

The melt blending of PBAT and PLA is a physical modification method, the main point of which is to require good compatibility between the two. However, the solubility of PBAT and PLA is quite different, so the compatibility is poor, and it is difficult to mix evenly.

Improving the compatibility of PBAT and PLA is the primary issue. It is necessary to add one or more compatibilizers during the blending process to improve the adhesion of PBAT and PLA interfaces. Commonly used compatibilizers are plasticizers, reactive compatibilizers, and tough polymers.

【Mechanical Properties】

PLA and PBAT have complementary properties, so there must be a mass ratio with good overall performance.

1. When the proportion of PLA increases to 40%, the tensile strength of the material first decreases and then increases, and the elongation at break first decreases significantly, and then remains stable.

2. If the PLA content is greater than 70%, the material is too brittle to be blown into a film. Therefore, the ratio of PLA to PBAT should be maintained at about 1:1 according to the additive situation.

【Degradation performance】

The reaction at the initial stage of material degradation is the entry of water molecules into the hydrolysis reaction. If it is a separate PBAT material, due to the rigid ester bond in the molecular structure, it is difficult for water molecules to enter, so it is not easy to degrade. However, PLA molecules are easily attacked by moisture and undergo internal degradation, so the higher the PLA content, the faster the degradation rate of the material.

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