Properties and enzymatic degradation of poly(acrylic acid) grafted polyhydroxyalkanoate films by plasma-initiated polymerization

Using plasma-initiated polymerization, poly(acrylic acid) (PAA) was grafted onto the film surfaces of polyhydroxyalkanoate (PHA), poly[(R)-3-hydroxybutyrate] (P(3HB)), and two kinds of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] (P(3HB-co-4HB)) with 4.7 mol% or 9.4 mol% of 4HB content. The graft ratio of PAA on the film surface increased drastically with acrylic acid concentration over 8%. Attenuated total reflection Fourier transform infrared spectroscopy demonstrated that the PAA grafted on the film surface was at least 70 nm thick. Mechanical and surface properties of PHA films grafted by PAA (PAA-PHA) were analyzed by tensile test, contact angle test, and scanning electron microscopy. While mechanical properties before and after plasma treatment remained unchanged, surface properties changed from hydrophobic to hydrophilic. Enzymatic degradation of PAA-PHA films was performed using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The rate of enzymatic degradation was inhibited by PAA graft. However, the rate of enzymatic degradability was accelerated by exposing ungrafted polymer to the enzyme solution, when a PAA-grafted film was divided into several pieces.