Thermoplastic Starch / Cellulose Nanofiber Nanobiocomposite Foam: Investigation on Thermal and Mechanical Properties

In recent years, has been increased production volume of polystyrene foams. These foams are applicable in food and packaging industries. Growing environmental concerns have created a need to develop biodegradable materials. Starch is a widely available, renewable, low cost, biodegradable and thermoplast (TPS). For these reason starch generates a great interest at it is considered as promising alternative to synthetic polymers (as polystyrene). But poor mechanical properties is a limited parameter to use this polymer. One of the important ways to reduce this limitation, is improvement of the thermal and mechanical properties using of nanofiber cellulose as reinforcement of foam. But NFC gel is aqueous and it forms irreversible aggregates when dried. High moisture create big cells in foaming and effect on foam properties. This subject limite using of NFC (nanofiber cellulose) to prepare polymeric composites. The aim of current research is using NFC (nanofibercellulose) to prepare NFC/TPS nanobiocomposite foam by extrusion mixing for better dispersion of NFC in matrix polymer and investigation on thermal and mechanical properties of foam.
Granules powder of corn starch, glycerol, NFC gel, and azodicarbonamide have been used to make NFC-TPS nanobiocomposite foam. Glycerol (30, wt %) as plastisizer. NFC (0.5, 1, 1.5, wt %) as reinforcing agent and azodicarbonamide (0.2, wt %) as blowing agent (BA) were used. Raw materials were mixed in a co-rotating two screw extruder. Then TPS/NFC/ BA granules was prepared. Then by using of these granules, nanobiocomposites foams were prepared under hot press (temperature higher than degradation temp of BA). The morphology of the samples studied by FE-SEM. The tests thermogravimetry (TGA), differential scanning calorymetry (DSC), dynamic-mechanical- thermal analysis (DMTA) were done on TPS/NFC nanobiocomposite foams for determination of the thermal and mechanical properties.
Findings: FE-SEM images showed, that TPS/ NFC nanobiocomposite foam has higher and smaller pores in comparison TPS foam. This is due to nucleation effect of NFC. TGA showed thermal stability of TPS/NFC nanobiocomposite foam with increasing of NFC. DSC showed transition glass temperature has been increased with increasing of NFC content. The DMTA showed storage modulus and loss modulus increased with increasing of NFC conten but tan delta decreased. The reason of this result is formation microcellular foam and reinforcment of the cell wall of foam by NFC.
the results of research showed NFC improved thermal and mechanical properties of TPS/NFC foam. TPS/NFC foam had more unique and smaller in comparison of TPS foam.