Binary blends of thermotropic liquid crystalline polyester (TLCP) and flexible chain polymer (FCP) were prepared in molten state. The TLCP adopted as the reinforcement were copolyesters of ethylene terephthalate and 60 mol% p-hydroxybenzoic acid (ET-HBA) and p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid (HBA-HAN). The FCP adopted as the matrix were polycarbonate (PC) and PET. Thermal/mechanical properties, morphology, and rheological properties of the blends were investigated by differential scanning calorimeter (DSC), polarizing optical microscope (POM), capillary rheometer and scanning electron microscope (SEM).
The P(ET-HBA)/PC blends were known to be partially compatible by thermal analysis and the surface transesterification reaction were observed between the two polymers at high temperature by POM. SEM studies revealed that the P(ET-HBA) component formed finely dispersed spherical domains with diameters of 0.2-2.0 microns in the PC matrix and the inclusions were deformed from the spherical droplets to fibrils as the blends were oriented in varying the draw ratio. The interfacial adhesion between the polymers was quite good and therefore it was confirmed that the LCP could act as a reinforcement of PC.
The P(HBA-HNA)/PET blends were completely incompatible and the interfacial adhesion between the two polymers was poor and therefore dewetting of the dispersed phase was observed in the oriented blends. The mechanical properties of the blends were enhanced remarkably due to the well developed rod-like microfibrils embedded in teh PET matrix. The skin-core morphology was observed in the injection molded specimens similar to the case of the fiber glass reinforced plastics.
From the rheological measurements minimum melt viscosity was observed at about 50% LCP concentration though the viscosity of the blend was largely dependent upon the shear rate, temperature, and composition. The dynamic storage modulus crossed over the dynamic loss modulus at 60% LcP. The existence of the yield stress which appeared only in the filled polymer system or polymer suspensions was also confirmed by the dynamic oscillatory shear measurements. At low concentration, the LCP acted as a nucleating agent for the crysallization of PET while at high concentration the LCP had an adverse effects.
열방성 액정 고분자와 엔지니어링 플라스틱의 이성분계를 용융하에서 블렌드하였다. 강화제로서 액정 고분자는 ethylene terephthalate (ET)와 p-hydroxybenzoic acid (HBA)의 공중합체인 P(ET-HBA), HBA와 2-hydroxy6-naphthoic acid (HNA)의 공중합체인 P(HBA-HNA)를 사용하였으며, 엔지니어링 플라스틱으로는 polycarbonate (PC)와 poly(ethylene terephthalate) (PET)를 각각 사용하였다. 블렌드의 열적/기계적 성질과 morphology, 유성학적 성질을 DSC, 편광 현미경, SEM, capillary rheometer 등을 이용하여 분석하였다.
열분석 결과 P(ET-HBA)/PC 블렌드는 부분적으로 상용성을 보였으며, 고온하에서는 두 고분자의 계면 사이에서 에스테르 교환 반응이 진행됨을 편광 현미경을 통하여 확인할 수 있었다. SEM 관찰 결과 P(ET-HBA) 액정은 PC matrix에 0.2-2.0 μ의 크기로 잘 분산되었으며, 배향에 의해서 구형의 입자가 섬유상으로 변형되었다. 두 고분자 계면 사이의 접착력이 매우 우수하여 액정은 PC의 강화제로 사용될 수 있음이 확인되었다.
P(HBA-HNA)/PET 블렌드는 상용성이 전혀 없었으며 계면 접착력도 불량하였으나 사출 성형을 통하여 액정이 섬유상으로 잘 배향되어 기계적 물성의 향상을 보였다. 또한 섬유 강화 수지에서와 같이 skin-core morphology가 관찰되었다. 유성학적 시험 결과 블렌드의 용융 점도는 측정온도, 전단속도, 조성 변화에 크게 의존하였으며 액정의 함량이 50% 일 때 최소값을 보였다. 동적 전단 시험 결과 액정이 60% 이상 함유될 경우 storage modulus 가 loss modulus 보다 크게 나타났으며 무기물 함유 고분자나 고분자 현탁액에서와 같은 항복 응력이 존재하였다. 액정의 함량이 작은 경우 액정은 PET의 기핵제로 작용하였으나 큰 경우에는 PET의 결정화를 오히려 방해하였다.
