【摘要】： 纖維增強(qiáng)復(fù)合材料在航空航天、軍工和能源等領(lǐng)域已得到廣泛應(yīng)用,隨著各種先進(jìn)技術(shù)的發(fā)展,對(duì)于復(fù)合材料性能的要求越來(lái)越高,需要開發(fā)新一代高性能增強(qiáng)纖維。聚丙烯腈(PAN)基碳纖維已經(jīng)商業(yè)化幾十年了,在所有商用的先進(jìn)纖維增強(qiáng)體中,它擁有最高的比強(qiáng)度和比模量。但目前傳統(tǒng)碳纖維在結(jié)構(gòu)方面存在各種缺陷,如纖維表面裂紋,孔洞,皮芯結(jié)構(gòu)等,限制了碳纖維性能的提高。因此,要制備更高性能的PAN基碳纖維,最有效的辦法就是減少各種結(jié)構(gòu)缺陷。本文通過靜電紡絲法制備了平行排列的PAN納米纖維膜,引入多步熱牽伸工藝,經(jīng)過預(yù)氧化和碳化,最終制得連續(xù)的高度有序排列且低缺陷的納米碳纖維,為制備高性能碳纖維探索出了一條新的途徑。 論文的主要研究如下： 1.研究了紡絲液濃度對(duì)于對(duì)纖維形貌的影響,并根據(jù)實(shí)驗(yàn)結(jié)果優(yōu)化了靜電紡絲工藝條件。只有當(dāng)PAN紡絲液濃度不低于14 wt%時(shí),才能制得形貌均一的PAN納米纖維。 2.制備PAN納米纖維膜,研究了PAN原絲、牽伸前后PAN納米纖維熱力學(xué)性能。PAN納米纖維在空氣中的環(huán)化反應(yīng)可以分為分子內(nèi)環(huán)化和分子間環(huán)化,分子內(nèi)環(huán)化與氧氣無(wú)關(guān),但分子間環(huán)化必須有氧氣的參與才能發(fā)生,且納米纖維的牽伸程度越大,越有利于分子間環(huán)化反應(yīng)的進(jìn)行。 3.引入多步熱牽伸的方法,對(duì)制備的PAN納米纖維膜進(jìn)行熱牽伸,研究了牽伸前后纖維的結(jié)構(gòu)與性能的變化。多步熱牽伸提高了纖維分子鏈取向,使纖維平行排列更加有序,纖維直徑分布趨于均一化。且有效減少斷絲現(xiàn)象,牽伸后纖維直徑從537 nm降低到412 nm。 4.優(yōu)化預(yù)氧化工藝,在張力作用下對(duì)PAN納米纖維預(yù)氧化,研究不同預(yù)氧化溫度和時(shí)間對(duì)納米纖維結(jié)構(gòu)的影響。隨預(yù)氧化溫度的升高和預(yù)氧化時(shí)間的延長(zhǎng),PAN分子鏈逐漸由鏈?zhǔn)浇Y(jié)構(gòu)轉(zhuǎn)化成梯形環(huán)狀結(jié)構(gòu),纖維的耐熱性不斷增強(qiáng)。280℃下預(yù)氧化120 min后,氧元素含量趨于穩(wěn)定值,表明環(huán)化反應(yīng)已基本完成,纖維被充分預(yù)氧化。 5.氮?dú)獗Ｗo(hù)下,在1200℃對(duì)預(yù)氧化的納米纖維進(jìn)行恒應(yīng)變碳化,制得納米碳纖維,對(duì)制得的納米碳纖維表面、內(nèi)部形貌和微觀結(jié)晶進(jìn)行了表征。納米碳纖維高度有序排列、表面光滑,粗糙度為0.249nm,纖維內(nèi)部結(jié)構(gòu)均一,無(wú)皮芯結(jié)構(gòu)缺陷。纖維大部分呈現(xiàn)亂層石墨結(jié)構(gòu),但部分晶區(qū)石墨片層平行排列,晶面間距為0.347 nm,晶層厚度為7-15層不等。 6.在聚醚酰亞胺中加入實(shí)驗(yàn)制得的納米碳纖維,對(duì)材料介電損耗沒有太大影響,但可以顯著提高材料的介電常數(shù),降低材料的電阻率。加入1.0 wt%納米碳纖維,聚醚酰亞胺的電性能改善效果要優(yōu)于同樣含量的碳納米管。
[Abstract]:Fiber reinforced composites have been widely used in aerospace, military and energy fields. With the development of various advanced technologies, the requirements for the properties of composite materials become more and more high, so it is necessary to develop a new generation of high performance reinforced fibers. Polyacrylonitrile (PAN) based carbon fibers have been commercialized for decades and have the highest specific strength and modulus of all commercial advanced fiber reinforcements. However, there are various defects in the structure of traditional carbon fiber, such as surface cracks, holes, skin core structure and so on, which limit the improvement of carbon fiber performance. Therefore, the most effective way to prepare higher performance PAN based carbon fiber is to reduce various structural defects. In this paper, PAN nanofiber films with parallel arrangement were prepared by electrospinning method. After preoxidation and carbonization, continuous, highly ordered and low defect carbon nanofibers were prepared by introducing multi-step thermal drafting process. A new way for the preparation of high performance carbon fiber was explored. The main research contents are as follows: 1. The influence of spinning solution concentration on fiber morphology was studied, and the process conditions of electrostatic spinning were optimized according to the experimental results. Only when the concentration of PAN spinning solution is not less than 14 wt%, the homogeneous PAN nanofibers can be obtained. PAN nanofiber membranes were prepared. The thermodynamic properties of PAN nanofibers before and after drafting. The cyclization of pan nanofibers in air could be divided into intramolecular cyclization and intermolecular cyclization, and the intramolecular cyclization was independent of oxygen. However, intermolecular cyclization can only take place with the participation of oxygen, and the greater the drafting degree of nanofibers is, the more favorable the intermolecular cyclization is. The structure and properties of PAN nanofibers were studied before and after drafting by the method of multi-step thermal drafting. The multi-step thermal drafting improves the orientation of the fiber molecular chain, makes the fiber parallel arrangement more orderly, and the fiber diameter distribution tends to homogenize. The fiber diameter decreased from 537 nm to 412 nm. 4 after drawing. The effects of different preoxidation temperature and time on the structure of PAN nanofibers were studied by optimizing the preoxidation process and preoxidation under tension. With the increase of preoxidation temperature and the prolongation of preoxidation time, the chain structure of pan was transformed into a trapezoidal ring structure, and the heat resistance of the fiber was enhanced continuously at .280 鈩，

本文編號(hào)：2246131