Effect of Simulated Weathering on Physicochemical Properties and Inherent Biodegradation of PLA/PHA Nonwoven Mulches

The effect of simulated weathering on the physicochemical properties and biodegradability of four fully biobased and potentially biodegradable agricultural mulches prepared nonwoven textile technology, consisting of randomly oriented fibers of average diameter 7–16 μm, has been investigated. Two mulches were prepared from polylactic acid (PLA) using spunbond processing, one naturally white and the other black (SB-W and SB-B, respectively), and two via meltblown processing, from 100 % PLA and a 75/25 w/w blend of PLA and polyhydroxyalkanoate [PHA; poly (3-hydroxybutyrate-co-4-hydroxybutyrate); MB-PLA and MB-PLA+PHA, respectively]. SB-W and SB-B possessed higher tensile strength than MB-PLA and MB-PLA+PHA (56.2N, 37.1N, 8.96N, and 3.90N, respectively). Simulated weathering introduced minor changes in physicochemical properties of SBs, but enhanced inherent biodegradability, yielding 68–72 % mineralization in 90 days. Simulated weathering greatly affected the physicochemical properties of the MB mulches, particularly MB-PLA+PHA, which underwent a 95 % loss of tensile strength, 32 % decrease of weight-averaged molecular weight (from 95.4 to 70.5 kDa), and breakage of microfibers, during a 21 days weatherometry cycle. Weathering accelerated the biodegradation of both MB mulches, with the time course of biodegradation and final extent of biodegradation (91–93 % in 90 days) nearly matching the value obtained for the cellulosic positive control. Fourier transform infrared spectroscopy suggested the SB and MB mulches underwent hydrolysis and photodegradative chain scission (Norrish Type II reaction). SB nonwovens may prove useful as biobased and compostable materials for multi-season mulching, and other long-term agricultural applications, such as for row covers in perennial cropping systems. MB nonwovens may be better suited for more traditional agricultural mulch applications.