The effect of extrusion conditions and the use of a compatibilizer in the crystallization of PBT/ABS blends

Abstract

Poly(butylene terephthalate) (PBT)/ acrylonitrile-butadiene-styrene (ABS) terpolymer blends were prepared in a twin screw extruder and the use of methyl methacrylate-glycidyl methacrylate-ethyl acrylate (MGE) terpolymer as compatibilization additive was evaluated. The effect of different screw profiles and mixing conditions were evaluated on the crystallization of the blends. Differential scanning calorimetry (DSC) was used to evaluate melting and crystallization behaviors of the PBT/ABS blends. The binary PBT/ABS blend has shown a double melting peak when cooled at lower cooling rates, mainly due to its melt-recrystallization during the heating up step. ABS has not affected the melting characteristics of neat PBT. The presence of MGE, as a reactive compatibilizer, in the PBT/ABS blends has reduced its heat of fusion and has partially inhibited its melt-recrystallization under heating. As result, it has prevented the occurrence of double melting peak. The epoxy functional groups of the MGE may react in situ to the carbonyls and hydroxyls end groups of the PBT molecules, thereby hindering the mobility of PBT molecules during the crystallization process due to its grafting to the compatibilizer molecules. The melt mixed blends prepared at lower feeding rate have shown a higher degree of crystallinity for the PBT/ABS blend, probably due to degradation of PBT caused by longer residence time in the extruder. The highest shear stress imposed to the blends at higher screw speed increased the degree of crystallinity of PBT, also due to its degradation.

Correlation between Processing, Morphology and Impact Resistance of PBT/ABS Blends

“…The possibility of degradation at low feeding rate and higher screw speed was investigated with a MGE-compatible PBT/ABS blend 10 . This study evaluated the effect of extrusion conditions and the use of a compatibilizer in the crystallization of PBT/ABS blends.…”

“…This study evaluated the effect of extrusion conditions and the use of a compatibilizer in the crystallization of PBT/ABS blends. It was observed that when the blends were submitted to these conditions they presented a higher crystallinity degree obtained by differential scanning calorimetry (DSC), and lower viscosity evaluated with capillary rheometry 10 . Blends processed with low feeding rate remain longer inside the extruder and therefore subjected to higher shear that could lead to PBT rich phase molecular degradation, which usually occurs by chain scission 14 .…”

“…As a result could occur increase in crystallinity and a reduction in impact properties. For the decrease in the impact properties with increased rotation speed, the degradation could occur by the increase of the shear rate and of the heat generated by the viscous friction 10 . The characteristic morphology of the non-compatibilized PBT/ABS blends is shown in Figure 4, where the dark regions are the dispersed phases of the ABS.…”

“…PBT/ABS (70/30) blend compatibilized in situ with the terpolymer methyl methacrylate-glycidyl methacrylate-ethyl acrylate (MGE) presents high impact resistance at low temperature. PBT/ ABS blend was studied to verify the influence of the process parameters on the morphology and end properties [7][8][9][10] . The results were very satisfactory and MGE stabilized morphology of the blend preventing coalescence of the dispersed phase, but partially reducing the influence of process parameters on the morphology of the blend.…”

Processing Stability and the Significance of Variation in Extrusion Speeds and Temperatures on SSB® 55 Pharma Grade Shellac for Oral Drug Delivery

“…As a consequence, the pressure to transport the melted blend through the screws becomes lower, causing the material to remain for a longer residence time in the extruder barrel, which would lead to the material remaining longer inside the extruder where it almost certainly is subjected to higher shear. Those processing conditions could lead to the polymer molecular degradation, which usually occurs by chain scission [7]. Therefore, Shellac short chains would have higher mobility to crystallize at higher crystallinity content.…”