Views: 0 Author: Site Editor Publish Time: 2025-06-16 Origin: Site
As power devices become more compact and operate at higher currents and switching speeds, localized hotspots can exceed standard polymer limits. Engineering plastics, when properly reinforced and modified, offer the thermal and dielectric robustness needed for reliable insulation in motors, transformers, and power electronics. This work focuses on three widely used systems and their tailored approaches to thermal stability.
Thermal Decomposition Temperature (Td): Temperature of 5–10 % mass loss via thermogravimetric analysis (TGA).
Glass Transition Temperature (Tg): Onset of polymer chain mobility measured by differential scanning calorimetry (DSC).
Heat Deflection Temperature (HDT): Temperature at which a specimen bends under a defined load.
High‑Temperature Dielectric Strength & Volume Resistivity: Measured under elevated temperatures to assess insulation degradation.
Epoxy systems offer high crosslink density, excellent adhesion, and good baseline Tg (~130 °C). Glass fiber reinforcement (30–60 vol %) further boosts dimensional stability and raises both Tg and Td. Proper silane coupling (e.g., γ‑glycidoxypropyltrimethoxysilane) enhances fiber–matrix bonding, mitigating interface debonding under thermal cycling. Typical performance:
Tg increase: 130 → 150 °C at 40 vol % glass fiber
Td (5 % mass loss): ~340 → 370 °C
Phenolic resins inherently char and resist heat, and can be reinforced with three substrate types:
Cotton Fabric (Woven): Provides flexibility and toughness. Ideal for molded parts; Tg ≈ 140 °C, Td ≈ 330 °C.
Phenolic Paper (Non‑woven): Offers uniform thickness and surface finish. Typical Tg ≈ 135 °C, Td ≈ 320 °C, used in flat laminates.
Phenolic Glass Fiber (Chopped/Mat): Combines high stiffness with thermal robustness (Tg ≈ 145 °C, Td ≈ 350 °C).
Across all variants, phenolic systems benefit from phosphorous‑based, halogen‑free flame retardants (10–15 wt %), which promote intumescent char layers and preserve dielectric strength at 200 °C.
Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) fibers deliver excellent tensile properties and low dielectric loss. Alone, these fibers have Tg ~ 80 °C; however, blending with high‑Tg thermosets or adding 5–15 wt % nano‑SiO₂/Al₂O₃ can boost Tg to 110–120 °C and Td by 30–40 °C. Long‑fiber mats or short‑cut strands can be molded into intricate shapes, with retained volume resistivity above 200 °C.
Nano‑Filler Incorporation:
3–10 wt % nano‑silica or alumina via in‑situ sol‑gel or high‑shear mixing restricts chain mobility, raising Tg and Td.
Network Crosslinking:
Multifunctional crosslinkers (e.g., triallyl isocyanurate) create denser networks. Optimal crosslink density (1.5–3 mmol g⁻⊃1;) increases HDT by 25–40 °C.
Halogen‑Free Flame Retardants:
Phosphorus/nitrogen systems (e.g., ammonium polyphosphate, melamine cyanurate) at 10–15 wt % achieve UL 94 V‑0 and enhance char formation without degrading dielectric strength.
Fiber Surface Treatment:
Silane coupling for glass fiber; plasma or chemical sizing for cotton and paper substrates improve interfacial adhesion and reduce microvoids under thermal load.
| System | Tg (°C) | Td (5% mass loss, °C) | Dielectric Strength Retention @200 °C |
| Epoxy + 40 vol% Glass Fiber | 150 | 370 | 88 % |
| Phenolic + Glass Fiber (Mat) | 145 | 350 | 85 % |
| Phenolic + Cotton Fabric | 140 | 330 | 82 % |
| Polyester Fiber + 10 wt% Nano‑SiO₂ | 115 | 360 | 80 % |
Tailoring engineering plastic systems to high-temperature electrical insulation requires a balanced approach to reinforcement, matrix chemistry, and additive selection. Key recommendations:
Epoxy‑Glass Fiber: Optimal for stiff, high‑load components.
Phenolic (Cotton, Paper, Glass Fiber): Versatile for molded parts and laminates with inherent char-forming capability.
Polyester Fiber: Best for complex shapes with moderate heat resistance.
Future work should explore self‑healing crosslinked networks, embedded thermal sensors for real‑time monitoring, and fully bio‑derived matrices to meet sustainability goals.
