Preparation and Mechanisms of Compatible Composite from Water Soluble Starch and Polycaprolactone

Generally, biodegradable composites from hydrophilic biomass such as starch and hydrophobic polymers show poor compatibility. In this work, Polycaprolactone (PCL) diol is used to synthesize PCL diol‐based polyurethane prepolymer (PCLPUP), and then the PCLPUP as a compatibilizer is mixed with water soluble starch and PCL in an intensive mixer for preparing compatible starch–PCL composites. Structural and morphological analyses show that the compatibility of the starch–PCL composite is significantly improved due to the existence of the PCLPUP interfacial layer. Consequently, the tensile strength, bending strength, and impact strength of the composite are enhanced greatly. Through the thorough purification and separation of starch–PCL composites, it is found that the compatibility mechanism mainly comes from two aspects. On the one hand, during the melting reaction, the PCLPUP forms PCLPUP interfacial layer and coats the water soluble starch filler tightly through urethane linkages. On the other hand, the PCLPUP interfacial layer interacts strongly with the PCL polymer matrix through PCL–PCL crystallinity. Therefore the PCLPUP interfacial layer plays an important role in the improvement of the compatibility of the composite. The graphical shows the schematic diagram of the formation of the compatible interface in the starch–PCL composite. The addition of the polyurethane prepolymer (PCLPUP) compatibilizer improves the interfacial adhesion between the PCL and the water‐soluble starch filler.