Polylactides: properties and prospects of an environmentally benign plastic from renewable resources

Abstract

Pressing environmental and economic concerns dictate the need to develop new synthetic macromolecules based on renewable resources. The vast majority of existing materials are based on non-renewable fossil resources that will eventually be extinguished. Manufacturing synthetic polymers and disposal by incineration produces CO 2 and contributes to global warming. For these reasons, poly(lactic acid) (PLA) polymers are of increasing commercial interest because they are derived from a renewable resources, sequester significant quantities of carbon dioxide relative to petrochemical based materials, conserve energy, and easily degrade. The mechanical properties of PLA are compared to other commodity plastics and it is shown that PLA closely resembles polystyrene. The effects of blending linear and branched chain architectures are discussed and it is shown that this provides a convenient method for controlling the elasticity and viscosity of the composite material without affecting mechanical or permeation properties. The melt rheology of high L content linear PLAs shows two unique features; they may be drawn to large Hencky strains without breaking and they exhibit considerable strain hardening. As a result, PLA is easily processed into fiber form. Due to the excellent combination of mechanical, rheological, and environmental properties, the prospects for widespread commercialization of PLA are excellent.