Caio G. Otoni
Federal University of São Carlos, Brazil
Title: Physical-mechanical properties of hydroxypropyl methylcellulose films as affected by molecular weight and methoxyl content
Biography
Biography: Caio G. Otoni
Abstract
Aiming at minimizing the environmental impact caused by the use of synthetic, non-renewable polymers, naturally occurring alternatives have been increasingly studied. Cellulose is a rigid, infusible, water-insoluble and fibrous-like biopolymer. In order to improve its film-forming properties, its hydroxyl groups are partially etherified into hydroxypropyl and methoxyl groups, resulting in hydroxypropyl methylcellulose (HPMC). We evaluated the effects of methoxyl content (MC) and average viscosimetric molecular weight (Mv) on glass transition temperature (Tg), water vapor permeability (WVP), tensile strength (σ), and elastic modulus (E) of films produced from aqueous film-forming solutions comprising 2% (w/v) of HPMC. We studied METHOCEL™ E15 (MC: 28-30%; Mv: 120,000 g.mol-1; Tg: 174 ˚C; WVP: 0.75 g.mm.kPa-1.h-1.m 2; σ: 31 MPa; E: 1.45 GPa), E4M (MC: 28-30%; Mv: 530,000 g.mol-1; Tg: 178 ˚C; WVP: 0.92 g.mm.kPa-1.h-1.m 2; σ: 67 MPa; E: 1.76 GPa), and K4M (MC: 19-24%; Mv: 550,000 g.mol-1; Tg: 210 ˚C; WVP: 1.52 g.mm.kPa-1.h-1.m 2; σ: 52 MPa; E: 1.74 GPa). Longer HPMC chains led to stronger (higher σ) and stiffer (higher E) films having higher Tg due to the increased physical entanglement and lower free volume and mobility. Films with higher MC were stronger due to the anchoring effect of methoxyl groups. Also, they presented lower Tg and WVP as a result of the lower occurrence of hydroxyl groups, that provide polarity and hydrophilicity. We demonstrated that both MC and molecular weight influence the physical-mechanical properties of HPMC films and should be taken into account in the development of novel bio-based materials with suitable properties.