A novel synthesis of light transmission from upcycled polyethylene terephthalate polymer and low-density polyethylene for greenhouse design in tropical climate

Abstract To support the circular economy in Thai’s agriculture, the main interviewed challenges point to knowledge and knowhow for greenhouse structure and system boosting up productivities. One popular material that possibly affected productivity is transparent polymer film, which can be recycled based on material property and blowing machine condition. This paper investigates the light transmittance performance of transparent polyethylene terephthalate polymer (PET) and low-density polyethylene (LDPE) sheets for use in low-energy greenhouses in tropical climates. The aim of the study is to optimize the thermal performance and light transmittance of these materials to support plant growth and human comfort. The study focuses on seven stages of plant growth, each of which requires different light characteristics including 1) seed, 2) germinating, 3) young seedling, 4) older vine, 5) flowering, 6) fruit bearing and 7) harvesting and drying. Each stage requires different light characteristics, e.g. light intensity, red light, blue light, white light and ultraviolet (UV) and pulsed light (PL). The methodology involves selecting PET and LDPE materials, preparing samples for thermal property and lighting laboratory tests and analysing the results based on suitable criteria. The findings show that LDPE sheets have 28.78% lower light transmittance than PET sheets, making them suitable for supporting the seedling stage and older vines of plant growth. PET sheets, on the other hand, deliver a high intensity of red light, making them suitable for stimulating photosynthesis in older vines and during the harvesting process. The study highlights the importance of considering both thermal performance and light transmittance when selecting materials for low-energy greenhouses in tropical climates.