| Polyethylene (PE) is widely used to manufacture agricultural mulch films. However, PE mulch films can not be degraded after their lifetime and tend to accumulate in the farmland, creating serious environmental pollution and soil deterioration. Using biodegradable agricultural mulch films is a promising way to solve this problem. Aliphatic polyesters such as modified poly(lactic acid) (PLA) or aliphatic-aromatic copolyesters such as Poly(butylene adipate-co-butylene terephthalate) (PBAT) are often used to produce biodegradable mulch films. Compared with conventional PE mulch films, the high cost and insufficient mechanical performance of biodegradable mulch films tend to restrict their wide application. PBAT has reasonably good thermo-mechanical properties and film blowing processibility. However, there also exist some obvious disadvantages such as poor anti-blocking property, low bubble stability, less thickness uniformity, poor weatherability and high cost. In order to develop biodegradable agricultural mulch films with excellent performance, in this work, domestic long chain branched (LCB) PBAT was used to produce different kinds of lOμm-thick ultrathin films with laboratory film blown equipment. Processing parameters were optimized to produce PBAT film with good anti-blocking property and thickness uniformity. In addition, chain extension and branching with multi-functional epoxide and melt blending with biodegradable polyesters poly(L-lactic acid) (PLLA) and poly(butylene succinate) (PBS) were employed to further modify PBAT films.Firstly, the addition of 1lwt% slip masterbatch containing 10wt% erucamide and optimum processing temperature can efficiently improve the anti-blocking property of PBAT. Effects of die gap, processing temperature, blow up ratio (BUR) and take up ratio (TUR) on the thickness, thickness uniformity and mechanical properties of the film were investigated. Die gap of 0.8mm and processing temperature of 160-185-185-185-180℃ have proved to be the most appropriate parameters for ultrathin film production. 10μm-thick ultrathin PBAT films with high thickness uniformity (standard deviation of thickness are about 3μm) and high transmittance were successfully prepared. The films have excellent mechanical properties, with small distinction between machine direction(MD) and transverse direction(TD). The tensile strength is about 40 MPa, the elongation at break is about 400% and tear strength achieves 150 KN/m.Secondly, chain extension/branching of PBAT was performed by reactive extrusion with 0.2wt% Joncryl(?)ADR4370s (ADR). In comparison with PBAT films, the resultant PBAT-ADR films are more flat and smooth, their thickness uniformity and elongation at break increase, and the tensile strength keeps almost unchanged. However, the tear strength and transmittance declines slightly.Thirdly,20wt% PLA and PBS were separately melting blended with PBAT to fabricate 10μm-thick PBAT-based blend films. The addition of PLA significantly improved anti-blocking property (without any erucamide), bubble stability, Young’s modulus and appearance of the film product. The mechanical performance of blend films produced with die gap of 0.8mm are superior to those produced with die gap of 1.5mm. Because of the incompatibility between PBAT and PLA, PBAT-PLA blend films show decreased mechanical properties and transmittance than PBAT films. 0.2wt% ADR was employed as a reactive compatibilizer and it effectively enhances the compatibility and interfacial adhesion of PBAT-PLA blends. The modified blend films with improved thickness uniformity and mechanical properties are prepared (tensile strength:25-30MPa, elongation at break:170-280%, tear strength: 100-110KN/m), however what is unsatisfactory is that elongation at break in MD is less that 200%. PBAT-PBS blends show better compatibility. The mechanical properties and transmittance of PBAT-PBS-ADR blend films are roughly equivalent to PBAT films and better than PBAT-PLA-ADR blend films. |
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