此外，环氧改性硅油、氨基改性硅油和聚醚改性硅油及其它添加助剂如抗静电剂、消泡剂等在亲水-亲油性能方面差异非常大，使用外乳化剂制备复配油剂乳液时，乳液胶束内油剂组成很难控制相同，另外复配油剂乳液中各种组分在聚丙烯腈碳纤维原丝表面亲和力差异非常大，由此导致聚丙烯腈碳纤维原丝生产过程中上油在原丝表面的油剂组成及剩留在油槽中油剂的组成不断改变，导致上油不稳定和不连续，由此严重影响原丝的连续稳定化生产及碳化后碳纤维的连续稳定化生产，是碳纤维企业不能连续稳定化生产T700、 T800 或更高等级碳纤维原因之一。
CURRENT DEVELOPMENT SITUATION OF AN OIL AGENT FOR A POLYACRYLONITRILE CARBON FIBER PRECURSOR AT BOTH HOME AND ABROAD
An oil agent/spin finish was applied to synthetic polyacrylonitrile （PAN ）carbon fiber precursor for ease of processing during manufacturing. An oil agent has an important impact on the hydrophilicity, bundling, fluffing, antistatic properties, friction resistance and temperature resistance (non-melting, non-sticking, non-merging and non- combustion) in the carbonization process of the PAN carbon fiber precursor. The research and development of the PAN carbon fiber precursor spin finish/oil agent in China falls behind when compared with foreign countries. The oil agent currently used in domestic carbon fiber production is reliant on imports. The imported oil agent is limited to one brand, is expensive and much is unknown about the formula due to confidentiality. Therefore, carbon fiber manufacturers lack the ability of independent formulation of the oil agent, resulting in the carbonization process of the PAN carbon fiber precursor in China being subject to the technical requirements of foreign oil agents. In addition, the high production costs seriously restrict the technological innovation and development of carbon fiber in China. Currently, the research work of a PAN carbon fiber precursor oil agent at home and abroad are mainly from colleges and carbon fiber manufacturing enterprises. Most enterprises focus on the impact of coating processes of the oil agent on carbon fiber quality, while the research direction of colleges mostly focuses on the reverse analysis of imported oiling agent composition and the formula research of functional composite oil agents. It is concluded that the most commonly used oil agent components are polyether modified silicone oil, amino modified silicone oil and epoxy modified silicone oil.
Polyether modified silicone oil is an amphiphilic polymer, which has both lipophilic and hydrophilic properties. When compounded with other components into a PAN carbon fiber precursor oil agent, it can play the role of a surfactant and reduce the surface tension of the oil agent.
Amino modified silicone oil contains strong polar amino groups which can interact with polar groups such as hydroxyl and carboxyl groups on the PAN carbon fiber precursor surface. As a result, it can be directionally adsorbed on the fiber surface, reduce the friction coefficient between fibers, and give the fabric a soft and smooth finishing effect. On the other hand, the amino modified silicone oil emulsification requires a large amount of emulsifier resulting in the finished fabric having disadvantages such as poor hydrophilicity or yellowing after long-term setting.
Epoxy modified silicone oil can improve the heat resistance of the PAN carbon fiber precursor and prevent the problems from softening, adhesion and merging of the PAN carbon fiber precursor in the pre-oxidation process. These problems eventually lead to a large number of fluffs, reduce the performance of carbon fiber, and reduce the production performance. In addition, an epoxy modified silicone oil, an amino modified silicone oil, a polyether modified silicone oil and other additives such as antistatic agents and defoaming agents have very different hydrophilic- lipophilic properties. When using external emulsifiers to prepare the compounding emulsion of the oil agent, the composition inside the micelles of the oil agent emulsion is difficult to control uniformly. Furthermore, the surface affinity and adhesion of various components in the compounding oil agent emulsion to the PAN carbon fiber precursor vary considerably. As a result, the constant change of the composition of the oil agent that is either coated on the fiber surface or remaining in the oil tank, during the extruded spinning process of the polyacrylonitrile carbon fiber precursor, results in unstable and undesirable properties of the PAN carbon fiber precursor that is coated by the oil agent. This further affects the continuous and stable carbonization of the PAN carbon fiber precursor to produce high quality carbon fiber. For the reasons stated, carbon fiber enterprises can not continuously stabilize the production of T700, T800 or higher grade carbon fiber.
Another point that requires stating is that there are issues in silicon based oil agents. Firstly, under high temperature conditions, silicon based oil agents will have cross-linked reactions and change happening from a liquid to a semi-solid colloid. This will not only result in a loss of lubrication, but also will lead to a merge between fiber monofilaments which may result in fiber winding, ultimately affecting equipment and production. Secondly, there will be a high-temperature heating process in the production of carbon fiber, and the inorganic silicon oxide transformed by the silicon oil agent remains in the interior or surface of the fiber. This may reduce the carbon content of carbon fiber and affect the performance. Due to this, some foreign enterprises and laboratories are developing low silicon or non-silicon oil agents. For example, it is mentioned in the patent of Japan Matsumoto Grease Co., Ltd. that silicon oil agents consist of ester compounds and polysiloxane as the main components. the polysiloxane accounts for 10% ~ 50%. The ester structure that can be used as a PAN carbon fiber precursor oil agent is shown in Figure 1 above and mentioned in the patent of Mitsubishi Rayon. an aromatic ester can also be used as the main component of carbon fiber precursor oil agent. The structure of aromatic ester is shown in Figure 2 avove.