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Biodegradable composites based on polylactide (PLA) and starch are obtained via solid‐phase mixing under conditions of shear deformation. The mechanical properties and biodegradability of composites under action of mold fungi as well as during exposure in soil are investigated. Using the scanning electron microscopy, the comparative study of the morphology of the initial samples and samples after biodegradation is carried out and the formation of structural defects resulting in sample destruction followed by fragmentation is revealed. The influence of PEG on mechanical properties and biodegradation process of the composites is shown. The analysis of composites by FTIR spectroscopy allows the estimation of the change in the PLA crystallinity and morphology of the film composites during the biodegradation in soil. The appearance of starch on the surface of films after exposure in soil enables a mechanism of biodegradation to be proposed.

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The ternary powder blends based on low‐density polyethylene (LDPE) and two polymers of natural origin poly(lactic acid) (PLA) and starch are obtained in a rotor disperser under conditions of shear deformations. The dependence of the final powder dispersity on the composition is explored. A comparative analysis of the mechanical properties of the ternary blends with those of the LDPE–PLA and PLA–starch binary blends previously obtained has revealed that the presence of two rigid polymers PLA and starch leads to an increase in the elastic modulus and a decrease in the tensile strength and elongation at break. In the study of the blend biodegradability, it is found that the presence of two polymers of natural origin in the system with a total mass fraction of 60% promotes intensive biodegradation.

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Under conditions of shear deformations, low‐density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X‐ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel‐permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47598.

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