Targeted biodegradability and physical properties of poly(butylene terephthalate-co-ε-caprolactone)

Suitable applications for a biodegradable polymer depend on its biodegradability ( Bd ), melting point (T m ) for thermal blending with biomass, tensile strength (σ) and tensile elongation (ε). A factorial experimental design was carried out in order to evaluate the targeted relationship among these properties, for synthesizing a novel biodegradable poly (butylene terephthalate-co-ε-caprolactone) (PBTCL). The results showed that the concentration of residual carboxyl end group ([COOH]) could inversely affect the number average molecular weight (M n ) and σ of PBTCL. Bd showed its loosely inversed relationship with crystallinity (X c ). The nuclear magnetic resonance (NMR) analysis showed the increased ratio of aromatic/aliphatic segments in PBTCL increased its T m , σ and Bd , but decreased ε and X c . The regression models from the experimental design of Bd , T m , σ and ε were plotted and overlaid; the targeted properties were achieved when the polycondensation temperature (T p ), the 1,4-butandiol/terephthalate (BDO/TPA), and the ε-caprolactone/terephthalate (CL/TPA) molar ratio were 255 °C, 1.39 mol/mol, and 1.48 mol/mol, respectively. Replicated PBTCL was synthesized under these optimal conditions, and the confirmed value of predicted Bd , T m , σ, and ε were 58.9 ± 0.4%, 115 ± 2.5 °C, 17 ± 0.8 MPa, and 356 ± 22%, respectively. The targeted PBTCL showed comparable properties to a commercially available biodegradable plastic.