Natural fiber biocomposites via 4D printing technologies: a review of possibilities for agricultural bio-mulching and related sustainable applications

Due to their perception as renewable and sustainable resources, natural fibres are becoming more popular as reinforcement in polymer matrix composites. The bulk of plant fibres is made up of lignin, hemicellulose, and cellulose with the balance composed of pectin, waxes, water-soluble organic components, and moisture (up to 20%). This study reviews and lists the existing studies conducted in 3D and 4D printing, their several techniques and material aspects. By utilizing the unique self-repairing capabilities of 4D printed polymers, which respond to factors such as temperature, humidity, osmotic pressure, magnetics, and biomolecules, a proposal is put forth to address the current unsustainable practices of agricultural mulching. Specifically, the proposal suggests the adoption of 4D printed bio mulch films that possess customized shape memory properties, serving as a sustainable alternative to conventional mulching practices. In line with the potential replacement with 4D printed bio mulch films, suitable bio-composites for the same are extracted and reviewed from literature along with their mechanical and microstructural properties, shape-memory behaviour, and their suitable 3D and 4D printing techniques in effective film synthesis and actuation programming. Moreover, several other agricultural applications that currently lack sustainability and where 4D printing can be deployed are discussed along with certain limitations and scope in developing 4D printed bio composite agro-sustainable structures.