【作者】 李慧；

【导师】 沈新元；

【作者基本信息】 东华大学 ， 材料科学与工程， 2008， 博士

【摘要】 热敏高分子膜是指当高分子膜所处的环境温度发生变化时,膜的水通量、截留率、孔隙率等随之发生敏锐响应,即突跃性变化的膜。广泛应用于生化物质的分离提纯、人工器官、药物控制释放和仿生科学等领域。羟丙基纤维素(Hydroxypropylcellulose,简称HPC)是一种主链结构为半刚性的水溶性非离子型纤维素醚衍生物。它是一种以天然纤维素为原料经化学改性制得的半合成型高分子聚合物,可溶于40℃以下的水中。同时HPC还是一种具有热敏性、可生物降解、生物相容性好、无毒的优良特性。适合在智能材料、包装领域、生物制药等领域广泛应用。目前,国内外对羟丙基纤维素膜的研究主要停留在羟丙基纤维素水溶液的成膜,以及在水溶液中与其它质子供体聚合物的共混改性等方面。对于在有机溶剂中将羟丙基纤维素作为质子的供体,与具有质子受体聚合物的共混改性方面的研究、以及羟丙基纤维素溶液的流变性能、羟丙基纤维素水溶液的传质凝固过程和热力学三元相图等方面的研究几乎未见报道。本文选用HPC和聚丙烯腈(简称PAN)两种聚合物为原料,以开发新型共混膜为主要目标,系统研究了HPC/PAN共混液的性能及共混膜的性能。利用多种手段分析了HPC/PAN共混体系的相容性及HPC/PAN共混溶液的流变性;利用膜渗透法从水通量、截留率以及孔隙率的角度对HPC/PAN共混膜的膜性能进行了表征;利用HPC具有LCST(Low critical solution temperature)的特点从溶胀-消胀法的角度对HPC/PAN共混膜的温敏性进行了表征。另外,本论文还对HPC纤维素膜的成形过程进行了理论分析和计算机模拟,绘制了HPC/水/甘油三元体系的三元相图、阐明了该体系在成膜过程中的传质过程。考虑到相容性是设计和开发新型共混材料的关键问题,论文首先从多角度对HPC/PAN共混体系相容性的研究。通过Hansen三组分溶解度参数(δ_d、δ_p、δ_h)的测定与计算,判定HPC/PAN共混体系在热力学上是不相容的;从总溶解度参数(δ)、以及混合热焓(△H_m)的理论分析得出该共混体系又基本属于相容体系或者部分相容体系。分析中采用的稀溶液粘度法、红外分析法、显微镜法、以及热重分析法所得到的结果与混合热焓的理论估计基本上是一致的。HPC和PAN两组分可以通过存在于-OH和-CN中的分子间氢键作用实现相容,在所研究的范围内HPC/PAN共混体系基本上属于存在界面相互作用的部分相容体系。考虑到聚合物的流变性是聚合物可加工性的重要量度,论文在设定不同含固量、不同组成、不同温度的条件下对HPC/PAN共混体系的流变性能进行了详细的研究。结果表明,30℃以下,不同浓度的HPC/PAN共混溶液的非牛顿指数n均小于1,且随着浓度的增大,n值不断减小:共混溶液均属于切力变稀流体,随着浓度的增大,同一剪切速率下的表观粘度随之增大。且在同一浓度下,随着PAN含量增大,共混溶液的表观粘度随之增大。HPC/PAN共混溶液的结构粘度指数△η随着浓度的增大而增大,16%时溶液的可成形加工性降低。随着温度的升高,n值不断增大;由于HPC在40℃附近发生相变,在30≤T≤40℃时,n值增加较多,T≥40℃时n值增加缓慢。30≤T≤40℃时,结构粘度随着温度的升高而降低;T≥40℃时结构粘度随着温度的升高而增加。T＜40℃时体系的E_η-值高于T≥40℃时体系的E_η,这是由于共混体系中HPC发生相转变,从而两种组分发生相分离,导致相畴增大的结果。在成型加工时选择的适宜加工温度应该小于40℃。在共混体系相容性和流变性研究的基础上,对HPC/PAN共混膜的渗透性、孔隙率以及温敏性进行了研究。结果表明,随着共混体系总含固量的增加,共混膜的水通量减小,截留率增大。水通量随着体系中HPC含量的增加而增大,截留率随着体系中HPC含量的增加而减小,表明HPC的加入能提高膜的亲水性。随预蒸发时间延长,膜的水通量降低,截留率上升。改变凝固浴组成和温度,可以调节共混膜的结构和性能。随着PAN含量的增大,共混溶液的相转变温度降低,且升温速率的快慢会影响共混溶液的相转变温度。在pH=1.4且温度在LCST以下时,HPC/PAN共混膜的溶胀速率随着体系中HPC用量的增大而增大,高分子链的松弛过程成为膜溶胀的控制过程。鉴于国内外迄今为止还没有对HPC水溶液成膜过程的详细描述,论文对HPC/水/甘油三元体系纤维素膜的凝固过程进行了计算机模拟。通过凝固点降低法测定了甘油与水的相互作用参数g12,发现该参数在不同质量浓度范围内随甘油含量的增加而增大,且处于1.4到2.0的范围内。通过平衡溶胀法测定出羟丙基纤维素与甘油的相互作用参数x13=2.08。成功计算了HPC/水/甘油三元体系的双节线和旋节线,并绘制出了该三元体系的相图。以Reuvers模型为基础,建立了HPC/水/甘油三元体系凝固过程的传质动力学模型。通过计算机模拟计算,根据聚合物在铸膜液内凝固过程中的浓度分布,考察了不同铸膜液浓度、不同凝固浴组成对传质过程的影响。得到膜在浸没的过程中,聚合物组分随着距膜表面距离的增加,体积分数逐渐减小。更多还原

【Abstract】 Thermo-sensitive macromolecular membrane was defined as a membrane,of which water flux,retention ratio and porosity discontinuously vaned with environmental temperature.They were widely used in isolation purification,artificial organs,drug delivery system and bionics,and so on.Hydroxypropylcellulose(HPC)is an alkyl-substituted hydrophilic cellulose derivative that not only shows particular phase transition behavior in aqueous solution or some organic solvents,but also has a lot of advantages such as excellent film-forming property,degradability,biocompatibility,and so on.It could be dissolved in water when water temperature was lower than its low critical solution temperature(LCST).In recent years,considerable research attention has been focused on its film forming from aqueous solution and modification by blending with proton donor polymers.But there were no reports on the modification of HPC by blending with proton acceptor,rheological behavior of HPC solution,and ternary phase diagram of film forming process for HPC.In this paper,with HPC and PAN as raw materials,the properties of blend solutions and the permeability of thermo-sensitive membranes were investigated in order to develop a new blend membrane.Based on the exsistance of LCST on HPC, the temperature-sensitivity of HPC/PAN blend membranes was investigated by swelling-deswelling.The membrane properties were characterized by water flux, retention ratio and porosity through permeation.In addition,both theory analysis and computer simulation of the film-forming process of HPC were presented,and the ternary phase diagram was drawn,thus,a mass transfer process was elucidated in the end.In consideration of compatibility which is a key factor in design and development of a new blending material.Firstly,a new blending solution of hydrogen-bonding-group-containing polymers HPC/PAN was studied.The compatibilitiy of the two polymers were investigated by means of FTIR,POM,SEM,△H_m,viscosimetry and TGA over the composition range.The three Hansen solution parameters of HPC were remarkably different from those of PAN though the total solubility parameters of the two polymers were approaching.It was concluded that this binary blend system was incompatible by theoretical calculation of the solubility parameters,but was found compatible by the experimental results.Because the viscosimetry more sensitively,simply and accurately reflected the changes of compatibility in polyblends,interaction parameters,Huggins constants and association constants that were calculated based on the viscosimetry were very creditable.The same results were also obtained from SEM,POM,TGA and FTIR analyses.The nature of compatibility of HPC/PAN was attributed to the hydrogen-bonding interaction between hydroxyl group and nitrile group when blending.In view of rheological behavior of polymer solution being an important factor of polymer processability,in the second part,the rheological behavior was investigated in detail at different concentrations,blend ratios and temperatures.The results showed that the non-newtonian index of HPC/PAN blend solutions was less thanl,and decreased with the increase of concentration below 30℃.The apparent viscosity increased with the increase of concentration at the same shear rate.The structural viscosity index also increased with the increase of concentration.Formability and workability of blend solution became worse when concentration was 16%.With the increase of temperature Non-newtonian index increased greatly,and structural viscosity index decreased in the range of 30-40℃.However,the results were on the contrary when temperature was higher than 40℃.The viscous flow activation energy of the blends in which temperature was less than 40℃was higher than that in which temperature was higher than 40℃.It was because that the phase transition in HPC occurred when temperature was higher than LCST,and then,the phase separation appeared,thus,phase domains increased.So,the suitable temperature of molding process was less than 40℃.Based on that,permeability,porosity and temperature-sensitivity of HPC/PAN blend film were studied in detail.The results were as follows:the water flux decreased and retention increased with the increase of solid content;the water flux increased and retention decreased with the increase of HPC content in HPC/PAN blends.It was indicated that the hydrophilicity of the blend membrane was improved by the addition of HPC.The water flux decreased and retention increased with the increase of prevaporation time.Adjusting coagulation bath composition and temperature could control structure and properties of blend films.The phase transition temperature of blending solutions decreased with the increase of PAN,and the phase transition temperature was influenced by warming-up rate.Swelling rate increased with the increase of HPC,and the polymer chain relaxation process became a controlling process during membrane swelling at pH=1.4 and temperature lower than LCST.Up to now,there was no detailed report about the process of film-forming from HPC aqueous solution.In this paper,computer simulation of solidification process in HPC/water/glycerol ternary system was studied.Solvent-nonsolvent interaction parameter was measured by freezing point depression.The results showed that the interaction parameter increased with the increase of glycerol mass fraction,and the value of solvent-nonsolvent interaction parameter was between 1.4 and 2.0.In addition,polymer-nonsolvent interaction parameter was determined by equilibrium swelling.The binodal and spinodal of HPC/water/glycerol ternary system were calculated,and the ternary phase diagram was drawn.A mass transfer dynamics model was established based on Reuvers mass transfer model.Effects of the casting solution concentration and coagulation composition on mass transfer process were investigated based on polymer concentration distribution during coagulation.The conclusion of this research was that the volume fraction of polymers was gradually decreased with the increase of the distance from membrane surface.更多还原