Soil Degradation of Polylactic Acid/Polyhydroxyalkanoate-Based Nonwoven Mulches

Abstract

The soil degradation of fully biobased agricultural mulches prepared from polylactic acid (PLA) and blends of PLA and poly3-hydroxybutyrate-co-4-hydroxybutyrate (polyhydroxyalkanoate, or PHA) using nonwoven textile technology was compared to that of a commercial biodegradable mulch film, BioTelo (Dubois Agrinovation, Waterford, Canada). The addition of PHA to PLA to the feedstock blend produced nonwovens that possessed lower tensile strength and molecular weight and increased the average fiber diameter of mulches. A meltblown (MB) nonwoven mulch prepared from a PLA–PHA 72/28 w/w blend underwent the greatest degradation, achieving a 78 % loss of tensile strength and a 25.9 % decrease of weight-averaged molecular weight during 10 and 30 week of soil burial, respectively. The mass fraction of PHA decreased during soil burial, suggesting the preferential microbial assimilation of PHA over PLA. BioTelo underwent a 29 % loss of tensile strength but no appreciable change of molecular weight for its chloroform-soluble components. In contrast, spunbond (SB) PLA mulches did not undergo any appreciable degradation during the 30 week soil burial studies. The results suggest that the MB–PLA + PHA nonwoven may serve as a potentially valuable biodegradable agricultural mulch, and that SB–PLA may be useful as a compostable material for long-term agricultural applications, such as row covers and landscape fabrics. A soil degradation study of MB–PLA + PHA that directly compared untreated compost-enriched soil to sterilized soil-compost mixture demonstrated that the loss of tensile strength occurred only in the unsterilized soil, suggesting this event is directly associated with soil microorganisms.