Fabrication of PBAT/polyethylene blends mulching film via blown film extrusion process

To extend the period of decomposition and property degradation of polybutylene adipate terephthalate (PBAT) mulching film for long-term use, PBAT was compounded with polyethylene mixture (LDPE: LLDPE = 15:85), calcium carbonate, and illite. PBAT mulching films were prepared using a blown film extrusion process with 80 mm diameter blowing die. To improve mechanical properties and processability of the film, crosslinking agent di-(t-butylperoxy isopropyl) benzene (BIBP) was added to PBAT compound and the effect of BIBP content on compatibility enhancement of PBAT and PE was investigated. Rheological measurements through dynamic oscillatory frequency sweep showed that the storage modulus of PBAT compound increased with the addition of BIBP and the slope of it decreased in the low frequency region because of crosslinking increase of PBAT and PE. Melt flow index of PBAT compounds decreased with increasing BIBP content. In the blown film extrusion process, the temperature of the heating zones in the extruder increased and the flow rate of the cooling air decreased with increasing content of BIBP. The highest output rate and a uniform surface morphology of mulching film were obtained because of a stable bubble with a tubular shape even at high extrusion speed with 800 ppm of BIBP. In addition, tensile strengths of both machine and transverse directions were the highest among all PBAT compounds. When the content of BIBP was higher than 800 ppm, the surface inhomogeneity of the film increased, resulting in decrease of the tensile strength in machine and transverse directions due to increased chemical cross-linking of PE and PBAT.