Multifaceted Evaluation of Plastics: Differences due to Kneading Condition

Significance of the Topic

Consistent control of molding conditions is critical in polymer processing because factors such as temperature, pressure, and kneading history strongly influence final material performance. Blended resins, in particular, may exhibit subtle changes in mechanical, thermal, optical, and chemical properties depending on the kneading treatment before or during injection molding. A comprehensive analytical approach is needed to identify these effects and guide optimization of processing parameters.

Objectives and Overview

This study evaluates the impact of kneading treatment on a 50:50 polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend by comparing two sample sets: Sample A (no prior kneading) and Sample B (kneaded with a dedicated machine prior to molding). Multifaceted measurements were performed to assess compositional homogeneity, thermal transitions, mechanical strength, optical changes, hardness, and molecular structure modifications.

Methodology and Instrumentation

Analytical techniques and conditions included:

• Fourier Transform Infrared Spectroscopy (FTIR, IRTracer™-100 with ATR diamond prism) to verify compositional uniformity at six specimen locations.
• Differential Scanning Calorimetry (DSC-60 Plus, heating rate 20 °C/min under nitrogen) to determine glass transition temperatures of the PC and ABS phases.
• UV-VIS Spectrophotometry (UV-2600i) to measure yellowness index based on reflectance across 380–780 nm.
• Tensile testing (AGX™-V universal tester, 5 kN load cell, 1 mm/min) for strength, modulus, and elongation at break.
• Microhardness testing (DUH™-210, Berkovich indenter, 500 mN load) to assess indentation hardness.
• MALDI-TOF Mass Spectrometry (MALDI-8020, 355 nm laser) to probe molecular end-group distribution of PC chains.

Main Results and Discussion

FTIR analysis showed identical spectra for both samples, indicating no change in composition due to kneading. DSC curves revealed glass transition temperatures near 110 °C (ABS) and 140 °C (PC) for both sets, with no significant shift. Tensile strength and elastic modulus remained virtually constant, but the breaking elongation of the kneaded Sample B decreased by ~40%. Yellowness index increased substantially from 3.44 to 12.99 with kneading, demonstrating optical degradation. Indentation hardness tests showed minimal variation between samples. MALDI-TOF MS detected a reduction in both-end capped PC molecules and a rise in hydroxyl-terminated chains, along with new signals attributed to reactions during extended kneading. These molecular changes correlate with observed decreases in ductility and color stability.

Benefits and Practical Applications

This multifaceted protocol enables a detailed understanding of how kneading influences polymer performance beyond standard mechanical and thermal metrics. By linking process history to molecular structure, manufacturers can fine-tune kneading and molding parameters to balance strength, ductility, and appearance in blended resins.

Future Trends and Potential Applications

Advances may include real-time in-line spectroscopic monitoring, integration of advanced mass spectrometry for more precise end-group analysis, and application of machine learning to predict optimal processing windows. Expanded use of combinatorial analytical platforms will support rapid screening of resin formulations and process conditions in industrial settings.

Conclusion

Kneading treatment prior to injection molding did not affect compositional homogeneity, glass transition temperatures, tensile strength, modulus, or hardness of PC/ABS blends. However, it led to significant increases in yellowness, reductions in elongation at break, and detectable alterations in PC end-group chemistry. This comprehensive evaluation approach provides valuable insights for optimizing polymer processing protocols.

Reference

Kawahara K., Yano F., Nishimura T., Yamazaki Y., Ohta M. Multifaceted Evaluation of Plastics: Differences due to Kneading Conditions. Shimadzu Application Note. First Edition: Oct. 2023.