The marriage of granular starch with synthetic polymers has given rise to a fascinating realm of thermoplastic starch compounds, heralding a new era of versatile materials. This article delves into the nuances of these compounds, exploring synthesis methods, applications across diverse industries, and the ongoing innovations in the field.
Synthesis Methods and Blending Techniques
Granular starch, while presenting challenges in processing highly filled polymer materials, undergoes a transformative journey when converted into a thermoplastic material. This metamorphosis is facilitated through extrusion processing, a technique that not only converts starch into a thermoplastic substance but also opens avenues for blending with synthetic hydrophilic polymers. The resulting blends seamlessly amalgamate the advantageous properties of both starch and synthetic polymers.
Poly(vinyl alcohol) (PVA): Pioneering the realm of starch-polymer blends, PVA stands as one of the first synthetic polymers to be intricately blended with starch. Techniques involved the preparation of cast films, with glycerol as a plasticizer and small amounts of formaldehyde as a crosslinking agent. To mitigate the embrittlement tendency over time, innovative plasticizers like sorbitol and glycol glycoside proved effective. Coating the starch-PVA films with hydrophobic polymers emerged as a strategy to augment wet strength.
Ethylene-Acrylic Acid Copolymer (EAA): The incorporation of EAA into starch-PVA-glycerol films demonstrated a delicate balance, enhancing elongation while avoiding brittleness. Strategic formulations involving casting aqueous dispersions or dry fluxing showcased the flexibility of blending starch and EAA. Further inclusion of polyethylene (PE) and additives such as ammonia contributed to the creation of transparent and flexible films.
Innovations and Research Frontiers
The interaction between starch and EAA has been a subject of extensive study, revealing the formation of a helical inclusion complex. This complex, explored through advanced techniques like chiroptical methods, x-ray diffraction, and NMR, attests to the intricate nature of starch-polymer interactions. The addition of PE, while introducing challenges of immiscibility, unraveled opportunities for unique structures during extrusion.
Innovations spearheaded by the Novon division of Warner-Lambert Company resulted in commercialized thermoplastic compositions. Blends of “destructurized” starch with hydrophilic and hydrophobic polymers showcased the versatility of these compositions. The term “destructurized” pertains to a process involving the heating of starch under pressure, leading to its transformation into a thermoplastic material.
Novamont, a division of the Ferruzzi Group, took a leap further by developing Mater-Bi products. These blends, comprising at least 60% starch and biodegradable synthetic polymers, exhibited properties akin to traditional polyethylene and found applications in creating water-impervious films.
Versatility in Thermoplastic Starch Compounds
The landscape of thermoplastic starch compounds is vast, offering a spectrum of compounds:
- Biodegradable Blends: Blends with biodegradable polyesters like polycaprolactone and PHBV expand the eco-friendly applications of thermoplastic starch.
- Laminated Structures: Starch blends contribute as layers in laminated structures, providing unique properties to the overall material.
- Mixing with Natural Polymers: Exploration extends to mixing thermoplastic starch with natural polymers such as cellulose esters and pectin.
- Deformation and Fracture Properties: Studies on the deformation and fracture properties of extruded starch shed light on factors affecting these properties, including moisture content, additives, and the type of starch used.
As ongoing research continues to unravel the mysteries of thermoplastic starch compounds, the potential applications are boundless. The ability to tailor properties through strategic blending opens doors to diverse industries, from packaging to controlled release matrices.
In the symphony of polymer science, thermoplastic starch compounds emerge as versatile notes, orchestrating a harmonious blend of natural starch and synthetic polymers. With applications spanning from eco-friendly films to innovative laminated structures, these compounds are not just materials; they represent a convergence of tradition and innovation, shaping the future of sustainable and adaptable polymers.