Miscibility with Thermal and Mechanical Properties for Poly(pentamethylene 2,6-naphthalate) and Poly(heptamethylene 2,6-naphthalate) Blends

Abstract

We have prepared the blends of poly(pentamethylene 2,6-naphthalate) (PPN) with poly(heptamethylene 2,6-naphthalate) (PHepN) by solution blending method and investigated their glass transition behaviour, melting behaviour, and tensile properties. It was observed that the blends of PPN/PHepN(9/1) and PPN/PHepN(1/9) have a single glass transition, reflecting a homogeneous phase, whereas those of PPN/PHepN(7/3), PPN/PHepN(5/5), and PPN/PHepN(3/7) exhibit double glass transitions, representing the existence of two phases. The PPN homopolymer annealed below 90 degrees C shows triple melting peaks (T-m1, T-m2, and T-m3). It was proved that T-m1 is attributed to melting of thin lamellar formed during secondary crystallization process, T-m2 to melting of thick lamellar created during primary crystallization, and T-m3 to melting of crystals recrystallized after melting the primary crystals at T-m2. For the annealed PHepN homopolymer, double melting endotherms (T-m1 and T-m2) were observed, caused by dual lamellar population with different thickness, i.e. T-m1 corresponding to the melting of secondary crystal and T-m2 to primary one. The Hoffman-Weeks plots, applied to the melting of primary crystals (T(m2)s), indicate that the equilibrium melting temperatures of PPN homopolymer, PPN/PHepN(9/1), and PPN/PHepN(7/3) blends are same to be 147 degrees C, and those of PHepN homopolymer, PPN/PHepN(1/9), and PPN/PHepN(3/7) blends to be 145 degrees C. Both the glass transition and melting behaviours demonstrate that the PPN/PHepN blend system is partially miscible. In addition, both the modulus and strength for the blends almost follow additive rule against blend composition, indicating that the PPN/PHepN blends are mechanically compatible over all blend compositions.