Compression Molding of Polyhydroxybutyrate Nano-Composite Films as Coating on Paper Substrates ^†

After successful preparation of master batch formulations including polyhydroxybutyrate (PHB) and fibrillated cellulose, the compositions of PHB with different types and concentrations of fillers were used for the deposition of a coating on packaging paper grades, by using compression molding technique in a hydraulic press. The resulting paper coatings are demonstrated to provide a green solution for the production of protective barrier layer films with tunable hydrophobicity and oxygen barrier resistance. The processing of the nanocomposites into flat and homogeneous coatings was optimized for different conditions of molding temperature and times, in particular, the flow conditions of the coating under pressing in contact with the paper substrate strongly depends on the presence of fillers. The effects of filler types on adhesion of the coating at the paper/polymer interface were investigated and the poor adhesion of native PHB coatings was improved after hydrophobic surface modification of the nanocellulose fillers. Under compression molding, the unique inclusion styrene-maleimide nanoparticles with encapsulated wax attached to the nanocellulose fiber surface enhanced the flowing properties of the coating by eliminating fiber agglomeration in contact with the paper substrate and reducing the effects of fiber pull outs. Therefore, hydrophobic fiber modification and the role of wax as a lubricant is necessary to obtain a homogenous dispersion during compressing molding of coating materials for papers.