Study On The Influence Of Secondary Sizing On Chopping Of Carbon Fiber Tow And Quality Evaluation

As one of the important application forms of carbon fiber, chopped carbon fiber has been widely used in industry field. Generally, carbon fiber tow needs to be sized secondly with sizing agent before its cutting in the current chopping process. A significant difference in the morphology and chopping process of carbon fiber tow before and after secondary sizing. In this paper, the morphology, drape angle and broken filament amount of carbon fiber tow after secondary sizing were investigated, and carbon fiber tow cutting experiments were studied, and quality of chopped carbon fiber in its production and processing was evaluated with fuzzy comprehensive evaluation method.This paper chose five concentrations of 1%, 2%, 3%, 4% and 5% of polyurethane(PU) sizing agent and five concentrations of 1%, 3%, 5%, 7% and 9% of styrene-butadiene rubber(SBR) sizing agent as secondary sizing agent to starch carbon fiber tow respectively, then obtained different types of secondary sizing carbon fiber tow(SSCFT). And macro profile, micro topography, drape angle and broken filament amount of these SSCFTs were investigated.This paper carried out three kinds of cutting experiment for SSCFTs with self-designed and constructed carbon fiber cutting experiment platform.(1)The first experiment was aimed to indicate the effect of different concentration on cutting process of SSCFTs, the results show that: the increasing speed of cutting force of PU-SSCFT in the unit time is less than non-SSCFT; there was an obviously decreasing fluctuation in the increasing process of cutting force of SBR-SSCFT(1% and 3% concentration); the cutting force of SBR-SSCFT(5% and 7% concentration) continued increasing until the tow was cut off; SBR-SSCFT could not be cut off when the concentration of SBR sizing agent was 9%.(2)The second experiment was aimed to indicate the effect of different concentration on cutting force and cutting time of SSCFTs, the results show that: cutting force of PU-SSCFT with different PU sizing agent concentration was similar, and less than non-SSCFT, but cutting time was not the same; cutting force and cutting time of SBR-SSCFT increased with the increasing of SBR sizing agent concentration.(3)The third experiment was aimed to indicate the effect of different tool feed rates on cutting force and cutting time of SSCFTs, the results show that: there were three stages in the change process of cutting force and cutting time of PU-SSCFT(3% concentration) and non-SSCFT, but two stages of SBR-SSCFT(5% concentration); cutting force of PU-SSCFT(3% concentration) was the smallest, non-SSCFT taken second place, and its cutting time was the smallest, cutting force and cutting time of SBR-SSCFT(5% concentration) were both the biggest.Four process parameters, including oven temperature, press roll pressure, cutter roll pressure and chopping speed, which affect the quality of chopped carbon fiber(CCF), were studied based on chopped carbon fiber production platform, designed by members of carbon fiber research group. Two kinds of CCF product, PU-CCF(3% concentration) and SBR-CCF(5% concentration), were taken as research objects. First, these two kinds of CCF product sample were obtained under different process parameters with orthogonal experiment. Second, several factors about CCF were chosen as quality evaluation indexes, including length dispersion, width uniformity dispersion, fracture section uniformity and fracture surface morphology. Third, quality of these two kinds sample was evaluated with fuzzy comprehensive evaluation method based on entropy weight. Finally, the optimum process parameters of those two kinds of CCF product were determined according to the evaluation results, and CCFs with the best quality were showed.