Degradable biopolymers such as polyhydroxybutyrate (PHB) are increasingly attractive for applications in bio-implants, renewable films and packaging. The stability and degradability of these materials can be affected by both the processing parameters and the environmental conditions under which the degradation is carried out. Degradation can be challenging to measure, particularly for samples with small masses and dimensions, such as thin films. We have developed an optical sensing system that enables sensitive monitoring of degradation in polymer thin film. In this system, the surface of the polymer film is patterned with a diffraction grating, and the sample is exposed to conditions enabling degradation. Monitoring the diffraction efficiency of the polymer film over time provides sensitive, real-time information about the surface stability of the polymer. In this contribution, we utilize this diffraction system to examine the effect of film thickness on the crystallinity and enzymatic degradation of PHB films. The physical properties of solvent cast PHB films of varying thicknesses were examined by atomic force microscopy (AFM, lamellar orientation) and x-ray diffraction (XRD, crystallinity). Using the diffraction system, we quantitatively determined that decreasing the film thickness of PHB, causes them to degrade faster. However, an extremely constrained ultra-thin film of PHB (thickness of ~ 40 nm) was found to exhibit resistance to enzymatic degradation, resulting in a discontinuous shift in the degradation rate as the PHB film thickness is decreased. This effect could be leveraged to design PHB films with tunable enzymatic degradation behavior.

Method for characterization and control of degradation in biopolymer thin films

254th National Meeting (2017)

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