为改善不透性石墨用浸渍剂酚醛树脂的耐高温性,用H3 BO3 和甲基三甲氧基硅烷(MTMS)为改性剂,制得B改性(BPF)和B/Si共改性的酚醛树脂(B/SiPF).研究结果表明,改性后 B 和 Si 原子接枝到树脂分子链中,形成B—O—C、Si—O—B键,热解温度t5%从改性前的 342℃提高到 353℃(BPF)和 367℃(B/SiPF),残炭率可达 70%(1 000℃).此外BPF-L和B/SiPF-L与石墨的接触角分别从改性前的 117.5°降低到 64°和 49°,改善了对石墨的浸润性.BPF和B/SiPF均可改善浸渍石墨的力学性能和耐高温性,且B/SiPF树脂能深入石墨的微小孔隙,结合更稳定,浸渍封孔效果更好.B/SiPF浸渍石墨的氧化失重率仅 0.40%(350℃空气),抗弯强度 23.55 MPa,比改性前提高 11.88%.
Study on boron-silicon modified phenolic resin and its impregnated graphite properties
In order to improve the high temperature resistance of phenolic resin for impermeable graphite,B-modified(BPF)and B/Si co-modified phenolic resins(B/SiPF)were produced using H3BO3 and methyltrimethoxysilane(MTMS)as modifiers,respectively.The results show that B and Si atoms are grafted into the molecular chain of the resin to form B—O—C and Si—O—B with large bond energy in the modification,respectively.The pyrolysis temperatures t5% of modified phenolic resin are increased from 342℃(unmodi-fied PF)to 353℃for BPF and 367℃for B/SiPF,and the char yield of 1 000℃is as high as 70% .Additionally,the wettability of modified phenolic resins on graphite has been improved.The contact angles of BPF-L and B/SiPF-L with graphite are reduced from 117.5°(before modification)to 64° and 49°,respectively.Both BPF and B/SiPF can improve the mechanical strength and high tem-perature resistance of impregnated graphite.The B/SiPF resin can penetrate into the tiny pores of graphite,which makes the combina-tion more stable and the sealing effect better,so it is more suitable as an impregnating agent for impermeable graphite.The oxidation weight loss of B/SiPF resin-impregnated graphite is only 0.40% in air at 350℃,and the bending strength of impregnated graphite is 23.55 MPa,which is 11.88% higher than that of the unmodified PF.
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