高聚物结晶动力学方程的研究

对国内外学者提出的高聚物结晶动力学方程进行了归纳,列举了较成熟的2种等温结晶动力学方程和7种非等温结晶动力学方程,分析不同方程产生的基础和存在的意义,总结现有方程的局限性,提出高聚物结晶动力学方程的研究方向。     

聚合物等温结晶过程的模拟实验

采用Monte Carlo法，利用计算机模拟预先成核条件下聚合物的等温结晶过程，研究了影响聚合物等温结晶过程的多种因素，如结晶体系外形、体系体积变化、晶核数目、晶体线生长速率等，基于Avrami方程的计算机模拟实验结果表明：与立方体体系比较，球体体系的结晶速率常数Z和Avrami指数n值更接近理论值；随着体系体积、晶核数目和晶核后期线生长速率的减小，Avrami指数n值随之减小；结晶后期晶核线生长速率的变化使得模拟实验曲线与理论值偏离严重。     

散现成核对聚合物等温结晶动力学过程影响的模拟实验研究

为研究散现成核对聚合物等温结晶动力学过程的影响，以聚对苯二甲酸乙二酯（PET）为样品，用计算机模拟聚合物等温结晶过程，建立晶核随时间变化的数学模型．结果发现，潜在晶核越快地转变成生长的晶核，模拟实验数据处理的曲线越早地偏离Avrami理论直线，散现成核是聚合物等温结晶实验数据处理曲线偏离理论直线的原因之一．     

“高聚物微体积元结晶动力学研究”项目通过天津市教委验收

由我校材料科学与化学工程学院董知之讲师等人承担的天津市高等学校科技发展基金项目“高聚物微体积元结晶动力学研究”，于2007年7月18日通过了天津市教委组织的专家组验收．[第一段]     

高聚物非等温结晶过程的Monte Carlo法模拟

采用Monte Cado方法模拟高聚物非等温结晶过程，获得PET试样在从熔体降温过程中相对结晶度随时间的变化曲线．通过Monte Carlo方法模拟曲线与DSC实验值的对比，发现通过调整结晶的起始温度和晶核数目可以使模拟曲线与实验值具有很好的一致性，表明所建模型正确，并为获取体系中晶核的数目和结晶起始温度奠定了基础。     

氢化棉籽油非等温结晶动力学研究

应用差示扫描量热仪(DSC)研究氢化棉籽油的非等温结晶行为.考察了两种氢化棉籽油在5、10、15和20℃/min降温速率下的非等温结晶行为,并用Ozawa方程进行动力学分析.非等温结晶曲线表明:随着降温速率的增大,结晶的温度范围增大;Ozawa方程解析非等温结晶曲线表明:当温度升高时,结晶常数m值增大,结晶速率常数K(T)减小.与等温结晶常数相比,非等温结晶常数偏大,说明非等温状态下氢化棉籽油结晶时可能会发生异相成核.     

纤维状β成核剂对聚丙烯非等温结晶动力学的影响

明晰纤维状β成核剂作用下聚丙烯(PP)的非等温结晶过程,对提升PP的力学性能至关重要。本文通过控制自组装β成核剂TMB-5为点状和纤维状形态,对比研究纤维状TMB-5对PP非等温结晶动力学的影响。结果表明:实验条件下,TMB-5不仅可使PP择优形成β晶,还可促进PP在高温成核,提高PP的结晶速率;不同于点状形态,纤维状TMB-5诱导PP冷却结晶时,α晶易在β晶生长前端异相成核,打断初始晶体的生长,使PP表现出非典型的3段生长模式和相对更慢的结晶过程。     

电子束辐照交联超高分子量聚乙烯等温结晶动力学

研究了电子束辐照交联超高分子量聚乙烯的等温结晶行为与辐照剂量、交联度和结晶温度的关系.首先,用差示扫描量热技术(DSC)研究了以0,50,100 kGy电子束辐照的超高分子量聚乙烯分别在不同的温度下等温结晶过程,发现半结晶时间(t1/2)和Avrami指数(n值)与结晶温度有关.与未交联超高分子量聚乙烯相比,交联聚乙烯等温结晶动力学的t1/2和n值较小,证明交联网络可加速聚乙烯成核,且抑制晶体生长.在此基础上,采用阶梯式温度"跃变"方法,诱导交联聚乙烯分子链在不同温度下分别结晶,得到具有多个熔融温度的交联聚乙烯结晶,而未交联的超高分子量聚乙烯则只显示单一熔融温度,证实了在交联聚乙烯中存在的不均匀交联网络结构导致分子链结晶能力不同.     

MC尼龙6／纳米ZnO复合材料等温结晶动力学的研究

采用原位聚合反应制备了MC尼龙6／纳米ZnO复合材料,并用差示扫描量热法（DSC）研究了MC尼龙6／纳米ZnO复合材料的等温结晶动力学。结果表明,在188～196℃时MC尼龙6及MC尼龙6／纳米ZnO复合材料结晶速率主要由成核过程控制。MC尼龙6／纳米ZnO复合材料的结晶速率G比MC尼龙6提高了0．1～0．3min^-1.研究发现,纳米ZnO的加入起到了异相成核的作用,提高了MC尼龙6的结晶速率。MC尼龙6和MC尼龙6／纳米ZnO复合材料的结晶速率G和结晶速率常数k均随结晶温度的升高而降低,半结晶时间t1/2和达到最大结晶速率的时间tmax随结晶温度的升高而缩短。但是MC尼龙6／纳米ZnO复合材料比MC尼龙6降低的幅度更大。     

尼龙6/11共聚物的非等温结晶动力学研究

以尼龙11预聚物和尼龙6预聚物为原料,采用熔融聚合的方法制备了尼龙6/11共聚物.利用差示量热扫描热分析仪(Differential Scanning Calorimetry,DSC)研究了尼龙6/11共聚物的非等温结晶过程,用经Jeziorny修正的Avrami方程对其非等温结晶动力学进行了研究,计算并得到非等温结晶动力学参数.结果表明:该方程适合于处理尼龙6/11共聚物的非等温结晶过程.在尼龙6/11共聚物非等温结晶过程中,在其初期结晶阶段可能同时包含了均相成核和异相成核,在二次结晶阶段结晶生长可能是一维生长;此外,还利用Kissinger方法求得尼龙6/11共聚物非等温结晶的结晶活化能为-201.76 kJ/mol.     

Influence of ZrO_2 on sintering and crystallization of CaO-Al_2O_3-SiO_2 glass-ceramics

1INTRODUCTION Nowadays,glassresearchersandarchitecture designersbecomeinterestedinthesinteringglass ceramics,anewlyappearingmaterialforarchitec turaldecoration[13].Comparedwithnaturalstone materials,sinteringglass ceramicsdecoratedmate rialshavethefollowingadvantages:densestruc tureandhighstrength.Itsbasicglasscomponents belongtoCaO Al2O3SiO2system.Becausenonu cleationagentisrequired,thissystemisattributed tothesuperficialcrystallizationmechanismofglass[4].Theproductionprocessofsinteri…     

Isothermal crystallization kinetics and melting behavior of poe-g-mah compatibilized PA11/POE blends

A new Nylon 11(PA11)/polyethylene-octene(POE) blends compatibilized by maleic anhydride grafted mixture polyethyleneocten(POE-g-MAH) was prepared through melt blending method.The isothermal crystallization kinetics and melting behaviors of PA11/POE blends were investigated in detail by differential scanning calorimetry(DSC) and polarized optical microscope.The n values of PA11 blending with POE or POE-g-MAH are almost similar with pure PA11,which indicates that the effect of POE and POE-g-MAH on nucleation and growth of PA11 crystal is slight.The overall crystallization rate of PA11/POE blends are higher than ones of pure PA11 at the same crystallization temperatures,but they decrease significantly when POE-g-MAH is added into PA11/POE blends.DSC heating curves of both PA11 and its blends exhibit two melting peaks,but the two melting peak become weaker when POE-g-MAH is add into PA11/POE blend systems.And the spherulite size is reduced significantly by the addition of POE-g-MAH compared with pure PA11 and PA11/POE blends.     

Effect of substrates on crystallization of high density polyethylene

The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystallization rate:the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer,which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum,brass and stainless steel plates,respectively.As to the dominant influence factor,the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil.Instead,we propose the plate’s ability of removing the latent heat of crystallization from the specimen.Rheological measurement is sensitive to the crystallization process.The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.     

矿渣微粉掺量对混凝土收缩开裂的影响

收缩开裂是现代混凝土劣化的重要原因.采用改进的椭圆环收缩开裂试验、自由收缩和抗折强度试验,以及不同养护条件下混凝土抗压强度对比试验来综合评价矿渣微粉掺量对混凝土收缩开裂的影响.结果表明,矿渣微粉掺量为40%～50%时,胶砂初始开裂时间明显增长,混凝土自由收缩减小,混凝土早期收缩开裂性能显著改善,混凝土抗压强度达到最高;标准养护条件比干燥养护条件对矿渣微粉混凝土强度的发展更有利.     

Influence of ZrO2 on sintering and crystallization of CaO-Al2O3-SiO2 glass-ceramics

ZrO2 was added into CaO-Al2O3-SiO2 glass-ceramics and the effect of ZrO2 on sintering and crystallization of CaO-Al2O3-SiO2 glass ceramics was investigated. The results show that the sintering shrinkage ratio of glass particles decreases with the increase of the content of ZrO2. ZrO2 has an unfavourable effect on sintering shrinkage ratio of glass particles. The sintering shrinkage ratio of glass particles increases with the increase of sintering temperature. The increase of sintering temperature favors the decrease of the liquid phase viscosity of glass particles. ZrO2 has little effect on crystallization of main crystalline phase （β-wollastonite）. However, it promotes the crystallization at relatively low temperature.     

废砖骨料对再生混凝土抗压与收缩性能的影响

以废砖粗骨料的等体积取代率为变化因素,在分析预吸水处理与裹浆处理条件下,废砖粗骨料等体积取代废弃混凝土粗骨料对再生混凝土抗压强度影响的基础上,着重探讨了废砖粗骨料体积取代率对再生混凝土收缩变形性能的影响。研究结果表明,等体积取代率为25%时,预吸水处理与裹浆处理均可最有效地降低再生混凝土的收缩变形,而对再生混凝土抗压强度却没有明显的降低作用。等体积取代率为25%时,预吸水处理下再生混凝土的抗收缩变形性能优于裹浆处理,而裹浆处理下再生混凝土抗压强度高于预吸水处理。     

Non-isothermal crystallization kinetics of kaolin modified polyester

Fiber-class modified kaolin and PET have been blended in the twin-screw and granulated to chips containing 4 wt% of kaolin.Non-isothermal crystallization process of kaolin modified polyester was investigated using a differential scanning calorimetry (DSC),and the addition of kaolin enhances either the melting temperature (Tm) or the crystallization temperature (Tc).The morphology of kaolin modified polyester,the melt of which is cooled at different cooling rate,was observed by scanning electron microscope (SEM).The relationship between Tc and cooling rate F was studied.Semi-crystalline phase t1/2 makes an exponential decline with increasing F,and the higher the cooling rate,the shorter the time of crystallization completion.Non-isothermal crystallization kinetics parameters and the activation energy were calculated,indicating that the higher rate of cooling needs the higher relative crystallinity in the unit crystallization time,the crystallization rate increased while speeding up the temperature reduction,and the activation energy ΔE was calculated to be-204.1566 kJ/mol for the non-isothermal crystallization processes by the Kissinger’s methods.