# Polylactide Composites with Mineral Fertilisers—Properties and Biodegradation

## TL;DR

This study examines how adding mineral fertilizers to polylactide composites affects their mechanical properties and biodegradation rates in different environments.

## Contribution

The study reveals that mineral salts enhance the mechanical performance and biodegradation of PLA–starch composites without altering their chemical or thermal properties.

## Key findings

- Mineral salts like MgSO4, KNO3, and Ca(NO3)2 improve the mechanical properties of PLA–starch composites.
- The addition of mineral salts increases the biodegradation rate of composites in soil and compost.
- Mineral salts do not alter the chemical structure or thermal properties of polylactide.

## Abstract

Additives strongly affect the decomposition rate of polylactide-based composites.

Biopolymer degradation is dependent on environmental conditions.

Mineral fertiliser components alter the mechanical performance of PLA–starch composites.

Polylactide (PLA) composites were prepared and doped with starch (10% by weight), and mineral salts used as mineral fertilisers (MgSO4, KNO3, Ca(NO3)2 and Ca3(PO4)2) were prepared. The content of the added fertilisers was 2% by mass in the composites. The tensile strength properties of the obtained composites were tested. The effect of the addition of fertilisers on the structure of polylactide was analysed using spectroscopic methods (FTIR and FTRaman). The thermal properties of the obtained composites were tested using thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). PLA composites with fertilisers were tested for biodegradability in two types of soil—field soil and horticultural soil—and in compost. Biodegradability was assessed based on the mass loss of biodegraded composites, spectroscopic tests and visual assessment of changes occurring in the composites. Tests were performed on the respiratory activity of microorganisms in the compost extract in which the tested composites were placed. The addition of mineral salts used in the tested composites significantly influenced the biodegradation rate of the composites. Mineral compounds (MgSO4, KNO3 and Ca(NO3)2) added to the PLA–starch composite improve its mechanical properties. It should also be noted that the addition of mineral salts to the prepared composites did not affect the chemical structure of polylactide. The addition of mineral salts to PLA also did not significantly affect its thermal properties, as demonstrated by DSC and TG thermal analysis.