Blends of PHB and LDPE were prepared by melt mixing in a twin screw extruder. Castor oil cake (CC) was used as filler for the blends. The design of experiments (DOE) technique was used to evaluate the effect of the components proportion on the materials properties. The mechanical properties and morphology of the materials were evaluated. The LDPE Young's modulus increases but the other tensile properties and impact resistance deteriorate with the addition of PHB or CC. The tensile strength values of binary mixtures of LDPE lie in the range from 8.9 to 10 MPa. As some commercial grades of LDPE have mechanical strength in this range, it may be inferred that the addition of a certain amount of PHB or CC to LDPE may be considered as a possibility for obtaining LDPE based materials with increased susceptibility to biodegradation. The poor interfacial adhesion between the phases became visible in all samples.

Blends of PHB and LDPE were prepared by melt mixing in a twin screw extruder. Castor oil pressed cake (CC) was used as filler for the blends. The mixture design technique was used to evaluate the effect of the components proportion on the materials flexural properties. The results show that superior LDPE flexural properties may be obtained by the addition of PHB or castor oil cake to LDPE. Biodegradation was evaluated burying the samples in simulated soil for different periods of time. The ternary mixtures with higher content of PHB showed more pronounced degradation. Under the experimental conditions studied the LDPE/CC compositions presented no degradation. However, the loss of mass of the LDPE/PHB/CC ternary mixtures was higher than the loss of mass of the corresponding LDPE/PHB binary mixture. This result suggests that the castor oil cake accelerates the degradation of the LDPE/PHB mixtures.

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