Study On Thermal Conductivity And Mechanical Properties Of Phenolic Resin Composites

Phenolic resin as a kind of century-long history typical representation of polymer with excellent chemical/thermal/flame resistance is widely used in aerospace, electric switch gear, mass transit and anywhere else that public safety are important. While its lower thermal conductivity (0.2 W·m-1·K-1) and lower mechanical properties that result from volatile content and the condensation reaction associated with the chemistry limits its further application in some field. The topic of this thesis is preparation the thermally conductive insulating phenolic resin composites made of several kinds of thermally conductive filler such as micro-sized magnesium hydroxide platelets, boron nitride sheets, chopped glass fibers and chopped polyimide fibers by choosing the proper technological process. In our thesis, the dosage of thermally conductive fillers and the cooperation of fillers on the thermal conductivity, electric conductivity, mechanical properties and flame/heat resistance of the composites were investigated. The works are mainly as follows:1. With magnesium hydroxide platelets and PF raw materials, a novel kind of thermally conductive insulating phenolic resin composite is prepared by solution blending, powder mixture and hot press molding formation. With a composite microstructure evolution model of different filler loading, we get different control factor for thermal conductivity in different filler loading. Finally, we suggest the best filler loading of this system is 60 wt%, and get a denser structure without defects such as voids and pores. The thermal conductivity of the system is increased about 6.6 times, while the mechanical properties are enhanced. The electric conductivity, flame-retardant properties and thermal resistance were well maintained.2. BN sheets have a flexible two-dimension plane structure with large diameter-thick ratio and weak surface modification. At constant filler loading of 60 wt%, with adding 1-20 wt% BN sheets, PF/BN/MH composites were prepared by solution blending, powder mixture and hot press molding formation. With a composite microstructure evolution model of adding BN sheets, the thermally conductive pathway of BN sheets was researched. Lots of magnesium hydroxide platelet was connected with single large BN sheet, while the BN sheet was forced by higher filler loading to form a thermally conductive network. With 20 wt% BN and 40% MH, the through-plane thermal conductivity of composites is 3.19 W·m-1·K-1, which shows about 16 times higher than the pure phenolic resin. The electric conductivity, flame-retardant properties and thermal resistance were well maintained, while the mechanical properties were enhanced.3. At constant filler loading of 60 wt%, with adding 1-20 wt% chopped PI fiber, PF/PI/MH composites were prepared by solution blending, chopped fiber premixing and hot press molding formation. In a relatively lower fibers loading (1 wt% chopped PI fiber and 59 wt% MH), the composites got a good thermal conductivity and better mechanical properties. Because of the weak interface between the chopped PI fibers and matrix, with the increase of the addition of the PI in composites, the thermal conductivity and mechanical properties decreased remarkably. The electric conductivity, flame-retardant properties and thermal resistance were well maintained.4. At constant filler loading of 60 wt%, with adding 1-20 wt% chopped GF fiber, PF/GF/MH composites were prepared by solution blending, chopped fiber premixing and hot press molding formation. With the increase of the addition of the GF in composites, the thermal conductivity decreases gradually while the impact strength significantly increases. The mechanical properties, electric conductivity, flame-retardant properties and thermal resistance were well maintained.