Reduction of poly(hydroxybutyrate-co-hydroxyvalerate) secondary crystallisation through blending with saccharides

A significant problem associated with the use of polyhydroxybutyrate and its copolymers in food packaging is their high initial crystallinity coupled with an ability to undergo secondary crystallisation over time which results in progressive embrittlement. This paper details work undertaken to hinder the secondary crystallisation process through the blending of poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) with mono-, di- and tri-saccharides. Following blending, the melt viscosity and melting point were observed to decrease with increasing saccharide concentration. The incorporation of saccharides into PHB-co-HV did not completely prevent the secondary crystallisation process, however, the rate of change in the Young's modulus and ultimate tensile stress were significantly reduced. The percentage change in the mechanical properties of these blends was found to be directly related to the size of the saccharide which was deemed to be as a result of greater steric hindrance and an increasing number of hydroxyl groups available for interaction with PHB-co-HV. This, along with the reduction in melt viscosity and melting point, makes the addition of mono, di and tri saccharides worthwhile for improving the processability and prolonging the effective life time of products made from PHB-co-HV.