No abstract

The major objective of this research was to modify PLA film surfaces with the ultimate aim of making a bioactive surface that will show faster degradation. The PLA film was solvent-cast, and the film surfaces were grafted with poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) using a UV-induced photopolymerization process. The film surface resulting from each reaction step was analyzed using ATR−FTIR spectroscopy and contact angle measurements. Results showed that PAA was grafted from PLA film surfaces in 2 or 3 h, while PAAm was grafted in 3 or 5 h depending on the method of activation. Films grafted with PAA and PAAm exhibited improved wettability. The neat and surface-modified films were incubated in different pH solutions, viz., pH = 4, 7, and 10, for specified time periods. The films resulting from each treatment were analyzed using atomic force microscopy (AFM). The molecular weights of the incubated films were measured using chloroform-based GPC. Results established that faster degradation of the PLA film when incubated in different pH solutions was achieved for PLA-g-PAA films; however, control studies revealed that the major contribution to the observed degradation was due to the entangled PAA chains resulting from acrylic acid monomer that migrated into the film bulk and not due to the surface-grafted layers.

The present research investigates the effect of photoinduced grafting reaction on the bulk properties of melt processed poly(L-lactic acid) (PLA)-poly[(3-hydroxybutyrate)-co-(3-hydroxyhexanoate)] (PHBHHx) blend films. PLA-PHBHHx blend films, comprising 10 wt % PHBHHx showed a remarkable toughness improvement. From dynamic mechanical analysis of melt processed PLA-PHBHHx blend films, the blend appears to be noncompatible. Unfortunately, PLA-PHBHHx blend films underwent rapid physical aging as characterized using differential scanning calorimetry, resulting in a significant toughness loss. Physically aged films regained the original toughness on annealing at 60 degrees C for 30 min. Annealed PLA-PHBHHx blend films also underwent physical aging leading to a significant toughness loss. Hydrophilic monomers like acrylic acid and acrylamide were successfully photopolymerized from the film surface using a sequential, two-step photografting approach. The resultant films were characterized using water contact angle goniometry, ATR-FTIR spectroscopy, and mechanical testing. PLA-PHBHHx blend films lost their toughness significantly on surface modification and this was assigned to UV-assisted solvent induced crystallization as characterized using wide-angle X-ray diffraction analyses.

The degradation of polymers under ultraviolet (UV) irradiation has been a great concern for biomaterial and agricultural applications. The major objective of this research was to study the effect of UV irradiation on the representative bulk and surface properties of poly (L-lactide) (PLA) films. Two UV sources with different spectral outputs and intensities were chosen so that one of them could be used for surface modification and the other could be used for UV sterilization of the PLA films. The results established that the molecular weight of PLA decreased significantly during irradiation from the photografting lamp under atmospheric conditions. Irradiation through a Pyrex container was shown to minimize polymer degradation during UV exposure from the photografting lamp. The PLA films UV-irradiated under the sterilization lamp for 12 h revealed a similar reduction in the molecular weight and no change in the surface hydrophilicity. However, significantly less photodegradation was observed under the sterilization lamp when the samples were held in a Pyrex container.

Coefficient of friction (COF) measurements and AFM of LLDPE films containing erucamide and behenamide indicated that COF reduction is not necessarily dependent on additive coverage of the film surface. A film containing 1010 ppm erucamide yielded a kinetic COF of 0.2 without complete surface coverage, whereas a 1080 ppm behenamide film exhibited a saturated surface and higher COF. AFM showed distinct differences in crystal formation between the surface-segregated additives, with erucamide exhibiting a plate-like structure.