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

Abstract

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 lm, 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 weightaveraged 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 longterm agricultural applications, such as for row covers in perennial cropping systems. MB nonwovens may be better suited for more traditional agricultural mulch applications.

Soil Degradation of Polylactic Acid/Polyhydroxyalkanoate-Based Nonwoven Mulches

“…The 25.9 % loss of M w for MB-PLA ? PHA-2 is the largest percent decrease obtained by the authors for all soil degradation studies conducted thus far, and is comparable to the 32 % decrease obtained for the same mulch when exposed to simulated weathering [43]. The chloroform-soluble components of BioTelo underwent only a 5.2 % decrease of M w (Table 4), which is much lower than the molecular weight decrease obtained for the same mulch during 3-4 month-long field studies conducted in 2010-2012, 14-18 %, and during 21 days of simulated weathering, 15 % (unpublished data).…”

“…In agreement, SB mulches subjected to laboratory-scale simulated weathering (ASTM G155 [42]) underwent only minor changes in physicochemical properties (e.g., tensile strength and fiber diameter), suggesting the long-term stability of SB mulches is not compromised by weathering [43]. Also, the SB PLA mulches did not biodegrade appreciably during soil burial studies in TN, TX, and WA [44].…”

“…In contrast, SB-PLA mulches underwent minimal changes of tensile strength and chemical properties during 30 week of soil burial. Given that the SB-PLA mulches did not undergo major physicochemical changes during simulated weathering, and are biodegradable under composting conditions [43], it is suggested that SB-PLA is a potentially useful biobased, compostable material for long-term agricultural applications, such as row covers and landscape fabrics. Column headings given in Tables 4 and 5 a Mean values were compared using Fisher's least significant difference (LSD) in SAS 9.3 software, with standard errors provided.…”

“…Also, the SB PLA mulches did not biodegrade appreciably during soil burial studies in TN, TX, and WA [44]. However, SB mulches were readily biodegradable under industrial composting conditions (ASTM D5338 [45]) [43]. Therefore, the SB materials are potentially useful compostable materials for long-term agricultural applications, such as multi-season mulching materials, row covers, and landscape fabrics.…”

“…The study showed that the addition of PHA enhanced soil degradation (e.g., reduction of tensile strength), and that the water delivery rate (500 vs. 1000 L per 48 h) and the addition of pineapple juice, an additional carbon source for microorganisms, did not have significant effect [50]. Simulated weathering of second-generation MB mulches, particularly those composed of PLA-PHA blends, led to the loss of tensile strength and molecular weight), which enhanced the inherent biodegradability [43]. An objective of this study is to provide a direct comparison of the first-and secondgeneration nonwoven mulches with BioTelo, a commercially available BDM film formed from MaterBi Ò , a proprietary blend of starch and proprietary polyesters, under conditions conducive to soil degradation (e.g., high soil moisture and the incorporation of compost; Experiment A [25,50]).…”