Plasticization Modification of PBAT/Starch Films

Starch-filled PBAT materials are completely biodegradable plastics. They have high degradation efficiency in a composting environment and can be completely biodegraded without any microplastic residues. They are the best materials to deal with white pollution and are also a research hotspot in recent years.

Using corn starch and PBAT as the main raw materials, glycerol as the main plasticizer, sorbitol and polyvinyl alcohol 200 as auxiliary plasticizers, the starch-filled PBAT film is made by extruder granulation and then blow molding. The plasticizing effects of different plasticizers in starch-filled PBAT materials were compared, and the effects of different plasticizers on the mechanical properties, surface roughness, water absorption and dissolution rate of composite films were also explored.

01 Basic formula

Based on PBAT, starch, ADR, and glycerin, the total addition amount of plasticizer 6% remains unchanged. Other auxiliary plasticizers are mixed with 1% and 5% glycerol. After the starch is stirred and mixed, it is prepared into starch-filled PBAT particles by a twin-screw extruder, and then blown into a film. The average thickness of the prepared starch-filled PBAT film was 0.040 mm.

02 Effects of plasticizers on mechanical properties of PBAT/starch films

It can be seen from Figure a that the addition of sorbitol and glycerol composite plasticizer (ie, 2# sample) can significantly improve the tensile strength and elongation at break of starch-filled PBAT film. After adding sorbitol, the tensile strength increased from the original 8.8 MPa to 12.8 MPa, the elongation at break increased from 532% to 710%, and the film properties were greatly improved; The tensile strength and elongation at break of the films made of polyethylene glycol, dimethylformamide and glycerol are lower than the plasticizing effect of single glycerin, and the tensile strengths are 6.1 MPa and 6.0 MPa, respectively. The intensity does not rise but falls.

It can be seen from Figure b that the composite plasticizer of sorbitol and glycerol (sample 2#) can significantly improve the impact strength of starch-filled PBAT film, and is better than the composite plasticizer of PEG200, dimethylformamide and glycerin.

Analysis shows that sorbitol has a higher chance of interacting with starch molecular chains than glycerol. Therefore, sorbitol plasticized films show higher intermolecular forces and increase the distance between molecules, thus providing better plasticizing effect, and the starch is further plasticized and dispersed, resulting in higher tensile strength, elongation at break and impact strength of the film.

03 Effect of plasticizer on surface roughness of PBAT/starch film

From the data, 2#<1#<3#<4#. The better the plasticizing effect of starch, the smaller the surface roughness of the film, the higher the film strength and the better the toughness. This phenomenon supports the influence of various plasticizers on the mechanical properties of the film from the side.

As can be seen from the above figure, the plasticizing and dispersing effect of plasticizer on starch is 2#>1#>3#>4#.

04 Effects of Plasticizers on Water Absorption and Dissolution Rates of PBAT/Starch Films

From the perspective of water absorption, the water absorption of starch-filled PBAT film is not much different, basically 2.5% to 3.0%.

From the dissolution rate, the film with 1# single glycerol as plasticizer has the highest water solubility. Sorbitol and PEG200 as auxiliary plasticizers of glycerol (samples 2# and 3#) have the same water solubility, which is slightly lower than that of single glycerin plasticizer. The dissolution rate of dimethylformamide (sample 4#) and glycerol composite plasticizer was the lowest. In terms of the dissolution rate, DMF can significantly reduce the dissolution rate of the film, but the harmful effects of DMF need to be considered.

05 Conclusion

(1) The effect of sorbitol and glycerin composite plasticizer on the plasticization, dispersion and particle size distribution of starch is better than that of single glycerin plasticizer, and also better than the composite plasticizer of PEG200, dimethylformamide and glycerol.

(2) The better the plasticizing effect of starch, the more uniform the particle size distribution, the smaller the surface roughness of the film, and the higher the tensile strength, pendulum impact strength and elongation at break of the film.

(3) From the perspective of water absorption, the moisture of the film mainly comes from the water absorption of starch, and the water absorption of plasticizer has little effect on the whole film.