Polymer Composites with Self-Regulating Temperature Behavior: Properties and Characterization

Area of Science:

• Materials Science
• Polymer Science
• Electrical Engineering

Background:

• Conductive polymer composites are essential for various applications, including self-regulating heating elements.
• Optimizing the balance between polymer matrix composition and conductive filler dispersion is crucial for achieving desired electrical properties.
• Understanding the thermal-electrical behavior of these composites under varying conditions is key to their practical implementation.

Purpose of the Study:

• To develop and characterize a novel conductive composite material with a homogeneous binary polymer matrix (HDPE/LLDPE) and a mixed conductive filler (carbon black/graphite).
• To compare the electrical and thermal properties of this new composite against a conventional HDPE-based composite.
• To investigate the effects of thermal cycling, radiation crosslinking, and preparation methods on the composite's performance, particularly its self-regulating heating capabilities.

Main Methods:

• Preparation of conductive composites using a binary polymer matrix (HDPE/LLDPE) and a mixed filler (carbon black/graphite).
• Comparative testing against a HDPE composite with similar fillers, including evaluation of electrical resistivity (ρ-T curves) and thermal behavior (DSC).
• Assessment of electrical stability under repeated thermal cycles and the impact of radiation crosslinking.
• Investigation of self-regulating heating properties by analyzing surface temperature and current intensity limitations at various voltages.

Main Results:

• The novel (CB + Gr)/(LLD + HD) composite exhibited comparable or superior properties to the (CB + Gr)/HD composite, even with lower filler concentration.
• Resistivity peaks were observed at the polymer matrix melting point, with the novel composite showing better electrical stability and less pronounced Negative Temperature Coefficient (NTC) effects during thermal cycling.
• Radiation crosslinking significantly increased resistivity (ρ_max) and inhibited NTC effects, enhancing material performance.
• Observed limitation effects in temperature and current intensity confirmed the potential for self-regulating heating applications below the melting temperature.
• Physical mixing proved more efficient for achieving low solid-state resistivity and high Positive Temperature Coefficient (PTC) effects, likely due to conductive particle distribution.

Conclusions:

• The novel conductive composite with a binary polymer matrix offers enhanced electrical stability and self-regulating heating capabilities compared to conventional composites.
• Radiation crosslinking is an effective method for improving the performance and stability of these materials.
• The preparation method significantly influences the electrical properties, with physical mixing favoring desirable PTC effects.
• Further optimization of preparation techniques and material properties is warranted for advanced applications.