【作者】 高向华；

【导师】 刘兆峰；

【作者基本信息】 东华大学 ， 材料学， 2008， 硕士

【摘要】 聚对苯二甲酰对苯二胺（Poly（p-phenylene terephthalamide）,PPTA）纤维是一种高性能的芳香族聚酰胺纤维,在航空航天、国防、复合材料等方面都有重要应用。本文利用热台偏光显微镜观察PPTA溶解过程及其溶液的液晶现象;通过差式量热扫描分析PPTA分子量、质量分数等因素对其液晶溶液熔融温度及相转变温度的影响;采用平板旋转流变仪研究PPTA-H₂SO₄液晶溶液的动态流变性质,分析讨论溶液温度、PPTA分子量及其分布、质量分数对复数黏度、损耗角正切、储能模量、损耗模量等参数的影响。通过对实验结果的数学拟合得到PPTA-H₂SO₄液晶溶液的非牛顿指数、零切黏度、松弛时间、黏流活化能等参数,以及建立了零切黏度与重均分子量之间的经验公式。通过上述实验结果分析为后续的纺丝工艺提供理论依据。采用双螺杆快速溶解得到PPTA-H₂SO₄液晶溶液进行纺丝。纺丝过程中通过改变纺丝溶液固含量、纺丝压力、喷丝板孔径、喷头拉伸比、卷绕速度、凝固浴温度和配比等因素研究其对纤维性能的影响;通过X-射线衍射、应力松弛、TG等实验手段深入研究纤维的结晶、取向等结构因素对其性能的影响。尝试在不同温度,不同停留时间和不同张力条件变化对纤维的机械性能的影响,初步探索得到高模PPTA纤维的热处理工艺。在PPTA溶解过程中是先溶胀后溶解,溶解一定时间后,PPTA溶液会出现液晶现象,在剪切作用下液晶现象更加明显。比较进口与自制PPTA配制的液晶溶液在偏光显微镜下拍摄的图片没有明显差别。采取先升温再降温再升温的过程进行差式量热扫描分析得到的相转变温度更为准确;升温时吸热峰均随PPTA的质量分数和分子量的升高向高温移动;当PPTA质量分数未达到19.5%时其溶液的熔融峰和相转变峰完全重合,在其熔融过程中同时伴随着相转变;反之,相转变过程在高于熔融温度下进行。PPTA-H₂SO₄液晶溶液是典形的切力变稀流体,随剪切频率的升高溶液的复数黏度迅速降低,损耗模量和损耗角正切tanδ逐渐升高并趋于缓慢增加,储能模量曲线几乎不变化;复数黏度、储能模量、损耗模量、损耗角正切随着溶液中聚合体质量分数和分子量的增加曲线上移,随着温度的提高而下移。PPTA-H₂SO₄液晶溶液流动曲线满足幂律方程,通过拟合得到非牛顿指数n都很小,严重偏离牛顿流体;n值随溶液中PPTA质量分数的升高、温度的降低、PPTA分子量增加而下降,但几方面对刀的变化影响都不大。PPTA-H₂SO₄液晶溶液满足Cross- Williamson方程,通过拟合得到零切黏度和松弛时间都随溶液质量分数的升高、温度的降低、PPTA分子量增加而上升;PPTA-H₂SO₄液晶溶液有很高的粘流活化能ΔE_η,随着溶液中PPTA质量分数和分子量的增大而略有增大。采用WLF方程根据时温等效原理将流动曲线最大扫描频率100rad·s^-1拓宽至接近1000rad·s^-1。不同温度下的logη₀～logM_w关系图,可以得到零切黏度η₀与重均分子量M_w之间的关系。vGP图中分子量越大相角的最小值就越小,平台模量G_N⁰=1.92E5。分子量分布不改变vGP图的形状,自制的聚合体比进口聚合体略窄。随着拉伸倍数的提高,喷出速度的降低,纺丝温度和纺丝原液固含量增加和聚合体比浓对数粘度的增大,纤维的断裂强度和初始模量均有显著增加,纤维断裂伸长率下降。喷出速度和拉伸倍数对纤维取向度的影响不明显;同时随喷出速度的增加纤维的结晶度变化不大,随拉伸倍数的增加,纤维结晶度增加,应力松弛率降低。较理想的纺丝工艺参数:浆液温度:80℃;浆液浓度:19%;喷丝板孔径:0.07mm;喷出速度:25～40m/min;拉伸倍数:6～7;凝固浴浓度:8～10%H₂SO₄;凝固浴温度:5℃;纺丝原液不能放置时间较长。随着纤维热处理温度的升高,纤维的断裂强度和断裂伸长率在下降,而初始模量在上升,断裂伸长率的CV值也在增加。随着停留时间的增加,热处理后纤维的断裂强度和初始模量先增加后下降,而断裂伸长率减小,其CV值不断增加;随着温度的增加,纤维热处理的停留时间越短,其断裂强度和初始模量越容易达到最大值。随着热处理中张力的增加,纤维的断裂强度和初始模量先增加后降低,断裂伸长率持续减小,断裂伸长率的CV值持续上升;随着温度的升高,纤维热处理的最佳张力降低。因此,进行张力热处理有助于提高纤维的断裂强度和初始模量。纤维初始模量和热处理后的模量是近似线性关系。随着纤维初始模量的增加,热处理后纤维的模量也在增加。热处理后,纤维的取向度有小幅的变化,结晶度的增加更加明显;热处理温度和张力的变化对纤维取向度和结晶度的影响不明显;随着热处理停留时间的增加,结晶度继续有小步的增加;随着热处理张力的增加,纤维的应力松弛率先下降后上升。本论文研究的主要创新点:（1）通过差式量热扫描两次升温法分析研究PPTA液晶溶液熔融及相转变过程。（2）系统分析了PPTA-H₂SO₄液晶溶液的动态流变性,及其影响因素。（3）建立了零切黏度与重均分子量之间的经验公式。（4）采用双螺杆快速溶解得到PPTA-H₂SO₄液晶溶液进行纺丝,制备出高强度、高模量的PPTA纤维。（5）直接热处理纺丝得到的PPTA纤维,制备出高模型PPTA纤维。更多还原

【Abstract】 Poly（p-phenylene terephthalamide）（PPTA）fiber is one of aromatic polyamide fibers with high performances and used widely in aviation,national defense, composite material and other industries.The resolving process of PPTA and its appearance of liquid crystalline（LC）were observed by micropolariscope with plate heating.Effect of molecular weight（MW）and weight concentration of PPTA on its melting temperature（T_m）and phase transition temperature(T_trans)were analyzed by differential scanning calorimetry（DSC）.Dynamic rheological properties of LC solution,effect of solution temperature,molecular weight（MW）and its distribution （MWD）of PPTA,weight concentration on complex viscosity（η（?））,loss tangent （tanδ）,storage modulus（G′）,loss modulus（G″）and so on,were studied with plate rotational rheometer,and parameters of PPTA-H₂SO₄ LC solution,non-Newton Index （n）,zero shear viscosity（η₀）,relaxation time（λ）and viscous activation energy（△E_η） were concluded and an empirical formula betweenη₀ and average viscosimetric molecular weight（M_W）was founded by fitting the experiment results with mathematic formulas.All of these conclusions are important references for the future spinning process.PPTA-H₂SO₄ LC solution was prepared by twin-screw for spinning. Effect of PPTA weight concentration,pressure,spinneret orifice number,draw ratio, wind-up speed,temperature and concentration of coagulation bath,et al,on fiber properties were discussed.Technology of heat-treating to get high-modulus fiber was investigated according to temperature,staying time and tension.In dissolving process,PPTA particles was swelling,then dissolving,and a few minutes later LC was appeared and more clearly with shearing.There was no obvious difference in micropolariscope photos of LC solution between imports and own.The T_transwas more accurate in process of heating,cooling and heating again by DSC,and the endothermic peak moved to higher temperature with raise of weight concentration and MW of PPTA.Phase transition was undergoing higher than T_m if weight concentration is larger than 19.5%,otherwise,melting peak and phase transition peak overlapped in melting process.LC solution is shearing sensitive liquid,η（?）decreased immediately,G″and tanδrose and G′was almost never changed,when shear rate（（?））increased.The curves ofη（?）,G″,G′and tanδwere higher with raise of weight concentration and MW,and lower with raise of temperature.The flow curves of LC solution fit with the Power Law and n,obtained by the Power Law,is very small,which means the solution deviated the Newton Liquid seriously.The n decreased when weight concentration and MW increased,when temperature decreased,and all these factors made tittles effects on it.The flow curves of LC solution fit with the Cross-Williamson Equation,andη₀ andλ,obtained by the equation,increased when PPTA weight concentration and MW increased,when temperature decreased.△E_ηof LC solution is large and larger a little as PPTA weight concentration and MW increased.The maximum scanning frequency（ω）of flow curves is 100rad·s^-1extending near to 1000rad·s^-1using the WLF Equation according to the Time-Temperature Equivalence Principle.Relation betweenη₀ and M_W were received according to the figures of logη₀～logM_W in different temperature. In vGP figure,minimum of phase angle is smaller as M_W is larger,plate modulus G_N⁰=1.92E5,and MWD wouldn’t change the vGP shape,and own’s is a little narrow than imports’.Breaking tenacity and initial modulus of PPTA fiber rose and elongation at break declined,when draw ratio rise,when spinning speed declined,when spinning temperature,weight concentration andη_inhof PPTA increased.Effect of spinning speed and draw ratio on fiber orientation is not obvious,and effect of spinning speed on fiber crystallinity is also not distinct,while fiber crystallinity increased,stress relaxation decreased with raise of draw ratio.The favorable parameters in spinning process are:dope temperature is 80℃;PPTA weight concentration is 19%;diameter of spinneret orifices is 0.07mm;spinning speed is 25～40m/min;draw ratio is 6～7; coagulation concentration is 8～10%H₂SO₄;Coagulation temperature is 5℃; spinning dope should be used as soon as possible.Breaking tenacity and elongation at break of fiber declined when heat-treating temperature rose,while initial modulus and its CV（coefficient of variation）increased. Breaking tenacity and initial modulus increased,then decreased,and elongation at break declined,its CV increased when staying time rose.Breaking tenacity and initial modulus reach the maximum more easily if heat-treating temperature rise and staying time shorten.When heat-treating tension increased,breaking tenacity and initial modulus increased,then decreased,and elongation at break decreased and its CV increased;when heat-treating temperature increased,appropriate tension of fiber heat-treating decreased.Relationship between initial modulus and heat-treated modulus is almost linear.Effect of heat-treating temperature and tension on fiber orientation and crystallinity is very little,its crystallinity increased a little with raise of staying time.Fiber stress relaxation decreased,then increased with increase of heat-treating tension.The new ideas mainly brought forward in this paper were as follows:（1） Melting and phase transition process of PPTA-H₂SO₄ LC solution is studied by the way of DSC.（2）Dynamic rheological properties and its influence factors are analyzed systemically.（3）An empirical formula betweenη₀ and M_W is founded.（4） PPTA fiber with high-tenacity,high-modulus is gained whose spinning dope is prepared in twin-screw.（5）PPTA fiber with higher modulus is prepared by means of heat-treating directly.更多还原