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

With the intensification of "white pollution" pollution, countries around the world have introduced stricter plastic restrictions.
Degradable plastic bags occupy major supermarkets and shopping centers.
If you look closely, 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 fruit or plant fruits, roots or leaves
.
There are hundreds of millions of tons of starch production in the world every year.

One of the renewable and biodegradable resources, with the advantage of being widely available and inexpensive
.
However, since natural starch has a microcrystalline structure and a granular structure, it does not have thermoplastic processing properties, so it needs to be transformed into thermoplastic starch to have thermoplastic processing properties
.

Amylopectin structure

Amylose structure

02.
PBAT

Polybutylene adipic acid/terephthalate (PBAT) is a class of degradable polyesters that has attracted much attention.
It has both the good mechanical properties of PBT polyesters and the good stretchability of aliphatic polyesters.
and ductility, and can also degrade into water and carbon dioxide under natural conditions
.

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

03.
PLA

PLA (polylactic acid) is also known as polylactic acid.
The production process of polylactic acid is pollution-free, and the product can be biodegraded to achieve circulation in nature.
Therefore, it is an ideal green polymer material and a representative of bio-based biodegradable plastics.
one
.

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

The chemical structure of PLA contains a large number of ester bonds, resulting in its 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 is modified
.

PBAT has soft texture, strong ductility and short degradation period; PLA has brittle texture, poor toughness and long degradation period.
Therefore, mixing the two is an excellent method to synergistically improve performance
.

04.
Introduction of PBAT/PLA material

【compatibility】

The melt blending of PBAT and PLA is a physical modification method, and the main point 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 uniformly
.

Improving the compatibility of PBAT with PLA is the primary issue
.
It is necessary to add one or more compatibilizers during the blending process to improve the adhesion between the 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 good quality ratio of comprehensive properties
.

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 and cannot be blown into a film
.
Therefore, the ratio of PLA to PBAT should be maintained at about 1:1 according to the additives
.

【Degradation performance】

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