Abstract
The degradation and stability of biodegradable films determine the service length of mulch films in actual use. Most biodegradable polymers degrade too fast to meet the required durability of mulch films. The objective of this work is to investigate the degradation behaviors of poly(butylene adipate-co-terephthalate) (PBAT)/polyhydroxyalkanoate (PHA) blend mulch films. Several different types of stabilizers were incorporated in the biodegradable blends to provide protection for the PHA/PBAT films during thermal processing and aging on agricultural fields. The degradation process of the films was systematically studied under an Accelerated aging test (AAT) and a Soil aging test (SAT). Adding a UV stabilizer, or antioxidant to the mulch films led to significant improvement in the retention of mechanical properties of the films under both AAT and SAT. Morphological evolution of the films with or without a UV stabilizer as a function of aging times was studied by Scanning electron microscopy. The results of thermal properties and crystallinity revealed damage of crystalline structure of the films during AAT. Spectrocopic results indicated that the films underwent both hydrolysis and photodegradative chain scissions (Norrish Type I/II reactions and photo-oxidation). Two degradation mechanisms of the PBAT/PHA biodegradable mulch films were proposed.
Highlights
Plastic mulch films have contributed to improving crop yields by increasing soil temperature, reducing water loss, and limiting weed growth, etc. [1], use of mulch films is especially important for arid regions around the world
The data showed that adding a UV stabilizer (UVA) or a hydrolysis resistance additive (HA) to poly(butylene adipate-coterephthalate) (PBAT)/PHA films slightly decreased both tensile strength (σ) and elongation at break of the biodegradable films, while adding an antioxidant (AO) led to a significant increase in tensile strength of the film, which could be attributed to decreased thermal degradation of the film in the presence of the antioxidant during the melt extrusion blending process and subsequent film extrusion
The results suggest that PHA is more degradable than PBAT under the repeated UV exposure and water spray cycles under Accelerated Aging Test (AAT) conditions, this is in agreement with a previous study which found PHA degraded faster than other polymers in accelerated soil degradation [38]
Summary
Plastic mulch films have contributed to improving crop yields by increasing soil temperature, reducing water loss, and limiting weed growth, etc. [1], use of mulch films is especially important for arid regions around the world. The polymers used in commercial mulch films are not biodegradable, polyolefins (PO) [2], ethylene-vinyl acetate (EVA), and polyvinyl chloride (PVC) [3] are the most common polymers used in manufacturing mulch films. As these polymer films remain intact after crop harvesting, and due to the high cost of film collection, these mulch films are typically plowed into soil as plastic fragments. There is a growing need to develop biodegradable mulch films which can provide the mulch functions during the crop growth but get biodegraded within a crop planting cycle. This has led to significant interest from both industrial and academic scientists to investigate material options to create biodegradable mulch films
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