Each of the two polycarbonates (PC) of different molecular weights was blended with acrylonitrile-butadienestyrene (ABS) to afford PC/ABS which was processed at several high-shear rates in order to study thermal behaviors. Changes in glass transition temperatures (T_gs) and thermal degradation behavior were measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. T_gs of both PC1 (MW=13700)/ABS and PC2 (MW=9700)/ABS gradually decreased as high-shear rate increased. Tg of PC1/ABS was higher than that of PC2/ABS at each condition of high-shear rate. PC/ABS without shear processing showed two TGA peaks which coalesced into one as high-shear rate was increased. The results indicated that high-shear rate processing could be utilized to improve compatibilities between blending mixtures but suffered from the disadvantages of thermal degradations above 3000 rpm and 20 s of high-shear rates.

ABS(acrylonitrile-butadiene-styrene)와 분자량이 다른 2종의 PC(polycarbonate)를 블렌딩하고, 고속전단압출성형기를 사용하였을 때 고속 전단에 의한 PC 분자량에 따른 열적 물성의 변화를 연구하였다. DSC(differential scanning calorimetry)와 TGA(thermogravimetric analysis)를 이용하여 유리전이온도와 열분해온도를 각각 측정하였다. 가해지는 전단력을 증가시킬 때에는 PC1(MW=13700)/ABS와 PC2(MW=9700)/ABS 두 가지 경우 모두 유리전이온도가 감소하는 동일한 경향을 보였다. TGA의 경우 전단력을 가하지 않은 경우 명확한 두 단계의 분해곡선을 나타내고, 고속 전단 가공을 한 경우 분해곡선이 선형으로 변화하는 경향을 보였다. 또한 고분자량의 PC를 사용한 PC/ABS 블렌드의 경우 저분자량의 PC를 사용한 경우보다 높은 유리전이온도와 열분해온도를 나타내었다. 이를 통하여 고속 전단 압출을 이용하여 상용성을 향상시킬 수 있으나 3000 rpm 이상의 고속전단을 가하면 블렌드 내의 열화가 발생한다는 것을 알 수 있었다.

Keywords: polycarbonate, acrylonitrile-butadiene-styrene, high-shear rate processing, differential scanning calorimetry, thermogravimetric analysis

Blends of different polymers can provide a material of new and much improved properties by reinforced synergism.^1,2 In our laboratory, blends of polycarbonate (PC) and acrylonitrilebutadiene-styrene (ABS) were studied under high-shear rate processing to study the effects on the thermal properties of PC/ABS blends.¹ PC/ABS blends have been widely used such as in electrical/electronics, telecommunications, and automotive applications.³ However, use of PC/ABS blends showed some drawbacks due to poor compatibilities between constituents.^4-8 In this regards, we had PC/ABS processed at high-shear rates to solve the problems arisen by poor compatibilities between PC and ABS.¹ We confirmed that high-shear rate processing had afforded much smaller sizes of dispersed phases of ABS in PC/ABS. Besides we observed that glass transition temperatures (T_gs) and mechanical properties of PC/ABS were decreased and changed, respectively, at high-shear rates,^1,9,10 conforming to the general phenomena observed in incompatible blends as compatibilities being improved. However, thermal degradation of PC arisen by high-shear force under high-shear rate processing was also observed to deteriorate the properties of PC/ABS.^1,9
In this regards, the purpose of this work was aimed to study any influences of PC, in terms of its molecular weight, on its blend with ABS in order to improve the impaired properties as was mentioned above. As is generally known, increase in molecular weight of polymer makes its processing rather difficult. However, it also provides some advantages in that smaller amounts can be used due to much improved properties of PC/ABS such as providing thinner layers. For the purposes two polycarbonates (PC) of different molecular weights were chosen to study influences exerting on the properties in PC/ABS under high-shear rate processing and hopefully to find out optimum conditions to develop a blended material of new and much improved properties.