Flexible starch-polyurethane films: Effect of mixed macrodiol polyurethane ionomers on physicochemical characteristics and hydrophobicity.

One of the most critical limitations in synthesizing starch-polyurethane (PU) hybrid materials is their microphase separation caused by physical incompatibility. This paper reports that the physical incompatibility and microphase separation between starch and PU can be overcome by using specifically designed anionic poly(ether-ester) polyurethane (AEEPU). The AEEPU was synthesised by preparing isocyanate (NCO)-terminated prepolymer using Isophorone diisocyanate (IPDI), 2,2-bis(hydroxymethyl)propionic acid (BMPA), poly (ethylene glycol) (PEG) and polycaprolactone (PCL). This AEEPU was physically mixed with glycerol plasticized high amylose starch (HAGS) at HAGS to AEEPU mass ratios of 90/10, 80/20, 70/30, 60/40, 50/50. Higher AEEPU content in HAGS-AEEPU increased surface hydrophobicity and elasticity while the Young's modulus remained unaffected. HAGS-AEEPU film at 50:50 ratio was comparable to LDPE film in terms of elongation at break (187%), Young's modulus (383 MPa), and contact angle (112°) and good transparency. These starch-PU films are expected to find increased application as biodegradable packaging materials.

Flexible starch-polyurethane films: Physiochemical characteristics and hydrophobicity.

Starch-polyurethane (PU) composite films with improved mechanical and hydrophobic properties were developed in this work. A simple and effective microwave-aided starch gelatinisation instrument was used to prepare glycerol plasticized high amylose starch (HAGS) material. Polyethylene glycol-isocyanate (PEG-iso) linker was prepared by reacting PEG 1000 with hexamethylene diisocyanate (HMDI). PEG-iso linker was then grafted into HAGS forming three dimensional urethane networks (PEG-PU). HAGS-PEG-PU composite blends were prepared and dried at ambient temperature to obtain HAGS-PEG-PU films. The mechanical properties and hydrophobicity (as contact angle, CA) of the HAGS-PEG-PU films were measured and analysed. Fourier transform infrared spectroscopy showed good grafting of PEG-iso into starch structure. Increase of PEG-iso concentration up to 20% (w/w) improved the molecular mixing and interpenetration between the starch and PEG-PU. The HAGS-PEG-PU films had improved hydrophobicity as indicated by CA values ranging from 51 to 110°and very high flexibility as evidenced from elongation at break (εB) values from 17 to 1000%. The HAGS-PEG-PU film formulation containing 20% (w/w) PEG-iso provided the best flexibility (εB>1000%) and hydrophobicity (CA>110°).