4D printing: Perspectives for the production of sustainable plastics for agriculture.

The concept of 4D printing of phase change materials is gaining attention in the potential development of self-healing materials for tissue engineering and manufacturing applications, but there has been limited utilization of the technology in agriculture/farm-based applications. The temperature-responsiveness, magneto-responsiveness, pH-responsiveness, and osmotic pressure-responsiveness of shape-memory materials have potential applications in green/compostable plastics for agricultural applications such as food packaging and mulching films, shade nets, and greenhouse polymer covers. The application of 4D printing in augmenting the biodegradability, environmental, economic, and production benefits of polymers in agriculture is the main focus of this review. So far,; little scholarly and industry attention have been directed to agricultural applications even though shape memory polymers are ideal for such applications compared to existing materials due to smart/intelligent behavior, optimized performance through fiber/nanomaterial reinforcement and multilayered composites. The practical constraints relate to the newness of the 4D printing process, customized synthetic routes for application-specific materials. The constraints can be resolved using novel and customized processes such as fused deposition modeling (FDM) and stereo-lithography and ink-jet printing, which are facile, scalable and affordable 4D printing techniques, that are highly effective compared to powder bed printing, and other droplet-based printing technologies, and photo-polymerization methods. FDM has led to the generation of PLA and other polymers with self-deformation and controllable shape memory effects. Future applications should overcome constraints linked to machine workload limitations and 3D/4D printing constraints.