"Poly (lactic acid) (PLA), a bio-based polymer derived from renewable resources, is an alternative to petroleum-based polymers because it reduces general dependency on oil availability and environmental concerns of common petroleum-based plastics, among others. Despite these attributes, PLA has relatively few commercial applications, concentrating mainly in the biocompatible biomedical device markets and as a commodity polymer for rigid containers and bottles used for packaging. However, its widespread applicability in flexible sheets/films is limited because of several drawbacks, among which its insufficient melt strength and low thermal stability, leading to narrow processing windows. Melt strength enhancers (MSEs) are often blended with PLA matrix to increase its melt strength, allowing the extrusion blowing and casting of the films. However, these additives are costly and not approved for food applications. Hence, there is a need to manufacture PLA films without any MSEs. Processing strategies were developed in this study to produce PLA blown films without any MSEs. Using a thermodynamic approach, the effects of various processing conditions and material characteristics on PLA's melt rheology (zero shear, shear and elongational viscosities) and film's blow-up ratio (BUR) were examined. Experimental results indicate that extrusion-blown PLA films could be successfully manufactured without MSEs, irrespective of PLA's degree of crystallinity, by tailoring the melt rheology through processing temperature and controlling other processing conditions such as the film's take-up ratio, as well as internal and external air pressures."--Page ii.
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