| 摘要: | 如何製造兼具高強度與高模數之碳纖維，一直是碳纖維產業發展上的重要議題。從過往的研究結果顯示，提升碳纖維強度的同時楊氏模數並未伴隨顯著的增進，但採取提升碳纖維楊氏模數的手段卻往往造成強度的下降，這就是碳纖維製造工藝的複雜與困難之處。聚丙烯腈 (polyacrylonitrile, PAN) 是製造高強度碳纖維的前驅體材料，又前驅體 PAN 纖維的品質往往是決定碳纖維最終性能的重要因素之一。故隨著碳纖維力學性能的向上突破日益困難，製程研究的重點也逐漸往前端 PAN 纖維的紡絲製程推移。近來 PAN 纖維的乾噴凝膠紡絲技術被認為是具有發展潛力，能同時提高燒成碳纖維強度與模數的新型紡絲技術。因此，本論文以自行設計之實驗室微型乾噴凝膠紡絲裝置為基礎，研究幾個PAN紡絲加工過程常見問題：(1) 纖維熱延伸倍率問題，由於PAN分子鏈有強極性的腈基側基，使得高分子鏈在強的分子鏈間相互作用下不易解糾纏造成纖維難以熱延伸的問題；(2) 熱穩定製程的放熱集中問題，PAN纖維在熱穩定的環化反應時的放熱，可能會導致纖維局部軟化，引發後續製程問題或燒成碳纖維品質不佳等問題；(3) 提高碳收率問題，PAN 基碳纖維是將 PAN 纖維經過一系列的氧化、碳化等反應，使鏈狀的分子轉變為石墨的平面結構，高的碳收率有助於碳纖維的性能與產率。目前一般製程的碳收率約為 ～ 53%，如何有效提升也是碳纖維研究的熱點之一。在這幾個問題的討論上，我們首先利用乾噴凝膠紡絲技術克服現行乾噴濕式紡絲的纖維皮芯結構問題。接著採取在 PAN 紡絲液簡單加入小分子添加劑的方法，取代 PAN 共聚物中共聚合成單元在環化反應中所扮演的角色。優點在於能解決上述問題的同時還能大幅簡化紡絲液製備。本研究選用的小分子添加劑有三種，其分別為：2,6-吡啶二羧酸 (2,6-pyridinedicarboxylic acid, PDC)、去氫膽酸 (dehydrocholic acid, DHCA)、單寧酸 (tannic acid, TA)。除了探討不同的小分子結構設計對改善放熱集中及提升碳收率的問題外，研究小分子添加劑對凝膠紡 PAN 纖維之熱延伸能力、微結構與纖維力學性能影響，也是本論文的重點。本研究首先透過傅立葉轉換紅外光譜儀 (FT-IR) 與熱示差掃描分析儀 (DSC) 探討小分子添加劑對環化反應的影響；接著利用熱重分析儀 (TGA) 分析碳收率的差異；最後利用PAN纖維的廣角X光繞射分析 (WAXS) 及單根纖維拉伸試驗探討凝膠紡絲PAN熱延伸纖維之微結構 (包含微晶尺寸、順向度、結晶度以及中間相結構) 與其力學性能的影響。研究結果顯示，小分子PDC的系統其在解決放熱集中問題、提高碳收率達 60.2%、更有助於提高熱延伸倍率達30倍以上時，製備具有 453.4MPa 的抗張強度、8.65GPa 楊氏模數為之高順向度、結構均勻 (無皮芯結構) 之高品質前驅體纖維。
How to manufacture carbon fibers with both high strength and high modulus has always been an important issue in the development of the carbon fiber industry. From previous research results, it has been shown that the Young's modulus is not accompanied by a significant increase in the strength of carbon fibers. However, the method increasing the Young's modulus of carbon fibers tend to result in strength decreased. This is the complexity and difficulty of the carbon fiber manufacturing process. Polyacrylonitrile is a precursor material for the manufacture of high-strength carbon fibers, and the quality of the precursor PAN fibers is often one of the important factors that determine the final properties of carbon fibers. Therefore, as the difficult breakthrough ,mechanical properties of carbon fiber becomes more difficult increasing, the focus of process research is gradually shifting to the front-end PAN fiber of spinning process. In recent years, dry-jet gel spun of PAN fibers has been recognized as a promising new spinning technology that can simultaneously improve the strength and modulus of sintered carbon fibers. Therefore, based on the self-designed laboratory small dry-jet gel spinning device, this paper studies several common problems in the PAN spinning process : (1) Fiber thermal extension ratio problem. Because the PAN molecular chain has strong polar nitrile side groups, the polymer chain is not easy to disentangle under the strong interaction between molecular chains, which makes hot drawing difficult use on the fiber.which makes the fiber difficult to thermally extend. (2) The heat release in the thermal stabilization process is concentrated, during the thermal stabilization cyclization reaction the PAN fiber releases heat , which may lead to part of fiber become soft, that cause the problems of the sintered carbon fiber like in the subsequent process or poor quality of the sintered carbon fiber. (3) To improve the carbon yield, PAN-based carbon fiber is a series of oxidation, carbonization and other reactions of PAN fiber. Converting chain-like molecules into planar structures of graphite. High carbon yield contributes to the performance and yield of carbon fiber. The carbon yield of the current general process is about ~53%. How to effectively improve is also one of the focus on carbon fiber research. In the discussion of these issues, first we use the dry-jet gel spun technology to overcome the fiber skin-core structure problem of the current dry-jet wet spun. Then, a method of simply adding small-molecule additives to the PAN spinning solution was used to replace the role of the copolymerized units of the PAN copolymer in the cyclization reaction. The advantage is that the above problems can be solved and the preparation of the spinning solution is greatly simplified. There are three kinds of small molecule additives selected in this study, which are : 2,6-pyridinedicarboxylic acid (PDC), dehydrocholic acid (DHCA), tannic acid (TA). In addition to discussing the problems of different small molecular structure designs to improve the exothermic concentration and the carbon yield. It is also the focus of this article to study the effects of small molecule additives on the thermal extension ability, microstructure and fiber mechanical properties of gel-spun PAN fibers. In this study, the effect of small-molecule additives on the cyclization reaction was first investigated by FT-IR and DSC. Differences in carbon production were then analyzed using a TGA. Finally, the microstructure (including crystallite size, alignment, crystallinity and mesophase structure) of gel-spun PAN thermally stretched fibers was investigated by wide-angle X-ray diffraction analysis (WAXS) and single fiber tensile test of PAN fibers. and its mechanical properties. The research results show that the small-molecule PDC system can solve the problem of exothermic concentration, improve the carbon yield by 60.2%, and help to increase the thermal elongation rate by more than 30 times. The Young's modulus is a high-quality precursor fiber with high conformity and uniform structure (no skin-core structure). |
