SA/CS-CaCl2/PMCG新型生物微胶囊的扩散与截留性能

通过测定不同相对分子质量的PEG传递透过SA/CS-CaCl₂/PMCG生物微胶囊的性能,确定了SA/CS-CaCl₂/PMCG膜的截留相对分子质量在2000左右。同时又测量了小分子物质葡萄糖、乳糖、乙醇和谷氨酸在3种SA/CS-CaCl₂/PMCG微胶囊中的扩散性能,并用数学模型计算出了这些物质在不同微胶囊的混合扩散系数D_m以及相应的微胶囊膜层中扩散系数D₁。结果表明： D_m随PMCG浓度的增大先增大而后呈减小趋势,而D₁则随PMCG浓度的增大而增大;并且D₁《D_m,说明微胶囊中的传质阻力主要在微胶囊膜层中。     

UHMWPE/LLDPE/HBP共混体系流变行为研究

为改善超高相对分子质量聚乙烯(UHMWPE)的加工流变性,将超支化聚酯酰胺(HBP)和线性低密度聚乙烯(LLDPE)与UHMWPE共混,研究了不同比例UHMWPE/LLDPE/HBP共混体系的流变行为。结果表明:UHMWPE/LLDPE/HBP共混体系熔体表观粘度随HBP质量分数的增加而减小;共混体系非牛顿指数<1,为典型的切力变稀流体;当剪切速率为10 s-1时,共混体系的粘流活化能较小;结构粘度指数随HBP质量分数增加而下降,随UHMWPE粘均相对分子质量增加而增大。     

马来酸酯烯类支化单体合成及其与甲基丙烯酸的共聚

采用三羟甲基丙烷(TMP)和马来酸酐(MA)制备多官能度烯类支化单体单三羟甲基丙烷三马来酸单酯(MTPTM)。MTPTM与甲基丙烯酸(MAA)在水溶液中通过自由基聚合,制备超支化聚合物。采用NMR表征了MTPTM和超支化聚合物的结构。考察了MAA和MTPTM单体摩尔比对超支化聚合物相对分子质量、水溶液黏度、热稳定性以及玻璃化转变温度的影响。结果表明,随MAA单体用量增加,聚合物相对分子质量及其分布先降后升,n(MTPTM)∶n(MAA)=1∶9时出现最小值(Mw=2.09×104,Mw/Mn=1.66),产物水溶液黏度也呈现先降后升的趋势,并在n(MTPTM)∶n(MAA)=1∶6时出现最小值。而玻璃化转变温度则先升后降,n(MTPTM)∶n(MAA)=1∶9时出现最大值(Tg=274.5℃),MAA单体比例增加,有助于超支化聚合物热稳定性提高。     

双峰PE生产工艺对其结晶行为和力学性能的影响

采用高温液相凝胶渗透色谱仪、广角X射线衍射仪和拉力机,研究了双峰聚乙烯(PE)生产中环管反应器和气相反应器的工艺参数对双峰PE产品的结晶行为和力学性能的影响。结果表明:环管反应器聚合产物的结晶度随停留时间的延长而减小,气相反应器产物的结晶度随n(H2)/n(C2H4)下降、n(1-C4H8)/n(C2H4)增大和床层分配率增加而减小,双峰PE的拉伸屈服应力和拉伸弹性模量随其结晶度和相对分子质量增加而减小。     

剪切稠化流体内气泡上浮运动特性

剪切稠化流体是一种典型的非牛顿流体,研究气泡在其中的运动特性对优化设备结构、提高反应效率具有重要意义。文中采用流体体积(VOF)法,通过改变Gallilei数(Ga)、E?tv?s数(Eo)与流变指数(n),对牛顿流体(n=1)及剪切稠化流体(n>1)内气泡的形状、尾涡、终端速度和气泡周围液相黏度分布的变化进行了深入的数值研究。结果表明:气泡变形程度和尾涡尺寸随着Ga数或Eo数的增大而增加;剪切稠化效应会阻碍尾涡的形成,减小气泡的尾涡尺寸;气泡周围剪切速率的差异会导致气泡上方及尾部产生高黏度区域,该高黏度区域会随剪切稠化效应的增加而增大;气泡终端速度随Ga数的增大或流变指数n,Eo数的减小而增大。     

超声波喷雾干燥微胶囊化橄榄油的存储稳定性研究

采用超声波喷雾干燥方法对橄榄油进行微胶囊化研究,探讨进风温度对橄榄油微胶囊含水量及包埋率的影响,进而评价微胶囊化橄榄油的存储稳定性。橄榄油的超声波喷雾微胶囊化研究结果显示：进风温度过高造成橄榄油微胶囊色泽加深,油脂析出,包埋率降低;进风温度过低导致橄榄油微胶囊干燥不充分,含水量较高。对喷雾干燥条件进行优化后获得橄榄油超声波喷雾微胶囊化条件：进风温度180℃,进料速率6 r/min。此条件下制备的橄榄油微胶囊包埋率可达98.2%。存储稳定性研究结果表明：橄榄油在不同光照、温度和湿度等条件下存储至30 d时,光照下微胶囊化橄榄油的过氧化值约是未包埋橄榄油的1/5,酸值约是未包埋橄榄油的1/3;避光下微胶囊化橄榄油过氧化值及酸值约是未包埋橄榄油的2/3;因温度升高,未包埋橄榄油氧化值增加1倍左右,酸值最大值可增加77.8%,而微胶囊化橄榄油过氧化值增加仅15%,酸值最大增加40.5%。微胶囊化橄榄油的过氧化值及酸值均低于未包埋橄榄油,微胶囊对橄榄油起到延缓氧化的作用,提高了橄榄油的存储稳定性。     

中和反应后pH值对溴化丁基橡胶结构与性能的影响

采用溶液法制备溴化丁基橡胶(BIIR),考察了中和反应后的pH值对BIIR微观结构、相对分子质量及其分布、溴含量和门尼黏度的影响.结果表明,随着中和反应后pH值的增大,仲位烯丙基溴的含量提高,而伯位烯丙基溴的含量下降;门尼黏度和相对分子质量随pH值增大而升高,且相对分子质量分布变窄.     

丙烯亚胺类外交联剂在压敏胶乳液中的应用研究

以丙烯亚胺类外交联剂(SAC-100)作为羧酸型丙烯酸酯PSA(压敏胶)乳液的改性剂,探讨了SAC-100掺量对PSA性能的影响,并采用DMA(动态力学分析)仪对固化前后乳胶膜的性能进行了表征。研究结果表明:引入SAC-100后,PSA的凝胶含量显著提高,凝胶部分的M_c(交联点之间平均相对分子质量)、溶胶的M_w(重均相对分子质量)或M_n(数均相对分子质量)不断减小;固化后乳胶膜的G′(储能模量)随SAC-100掺量增加而增大,相应PSA的内聚强度、持粘力提高;乳胶膜的tanδ(力学损耗因子)随SAC-100掺量增加而减小,相应PSA的初粘力和剥离强度降低。     

加成型Si/Ti杂化树脂胶粘剂的制备及其性能研究

以乙烯基三乙氧基硅烷、端羟基聚二甲基硅氧烷(107硅油)和钛酸四丁酯(TBT)为原料,采用水解缩合法制备出一种无溶剂型Si/Ti(硅/钛)杂化树脂胶粘剂。研究结果表明:该杂化树脂的拉伸强度、冲击强度随TBT掺量增加而增大;随着原料配比中107硅油掺量的增加,该杂化树脂的拉伸强度下降、冲击强度增大;该杂化树脂胶粘剂的剪切强度随TBT掺量增加、固化时间延长或固化温度升高而增大;玻璃基材表面经硅烷偶联剂(KH-560)处理后,相应胶接件的剪切强度相对最大,并且该剪切强度随KH-560掺量增加而增大。     

不同相对分子质量的尼龙6流变性能研究

用毛细管流变仪研究了尼龙 6试样相对分子质量对其流变性能的影响。结果表明 ,在实验范围内试样熔体为假塑性流体。随着相对分子质量的增加 ,非牛顿指数 (n)减小 ;熔体稠度 (K)增大 ;lgη～lg γ直线的斜率和截距均增大 ;粘流活化能降低。且试样的相对分子质量与表观粘度及熔融指数均有较好的对数线性关系。     

Crystallization and morphology of cholesterol end‐capped poly(ethylene glycol)

Crystallization and morphology of polyethylene glycol with molecular weight M_n = 2000 (PEG2000) capped with cholesterol at one end (CS‐PEG2000) and at both ends (CS‐PEG2000‐CS) were investigated. It is found that the bulky cholesteryl end group can retard crystallization rate and decrease crystallinity of PEG, especially for CS‐PEG2000‐CS. Isothermal crystallization kinetics shows that the Avrami exponent of CS‐PEG2000 decreases as crystallization temperature (T_c). The Avrami exponent of CS‐PEG2000‐CS increases slightly with T_c, but it is lower than that of CS‐PEG2000. Compared to the perfect spherulite morphology of PEG2000, CS‐PEG2000 exhibits irregular and leaf‐like spherulite morphology, while only needle‐like crystals are observed in CS‐PEG2000‐CS. The linear growth rate of CS‐PEG2000 shows a stronger dependence on T_c than PEG2000. The cholesterol end group alters not only the free energy of the folding surface, but also the temperature range of crystallization regime. The small angle X‐ray scattering (SAXS) results show that lamellar structures are formed in all these three samples. By comparing the long periods obtained from SAXS with the theoretically calculated values, we find that the PEG chains are extended in PEG2000 and CS‐PEG2000, but they are once‐folded in CS‐PEG2000‐CS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2464–2471, 2007     

Dependence of the Avrami Exponent on Supercooling During Nonisothermal Crystallization of Poly(phenylene sulfide)

The nonisothermal crystallization behavior of poly(phenylene sulfide) (PPS) was studied by means of differential scanning calorimetry (DSC) at various cooling rates. The nonisothermal crystallization data were analyzed by the Ozawa theory. The Avrami exponent n was determined at several constant cooling rates. A notable variable trend of the Avrami exponent with the temperature was found. Within 215–238°C and 243–255°C, the Avrami exponent of PPS increases markedly with the increase of temperature, respectively, while within narrow temperature range from 238°C to 243°C, a sharp decrease of the Avrami exponent can be seen. It has been suggested that the nuclei formation and the geometry of spherulite growth in the nonisothermal crystallization of PPS are strongly affected by the temperature and correlated with the Regime Transition (the regime II→III transition for PPS).     

On the use and misuse of the avrami equation in characterization of the kinetics of fat crystallization

The Avrami model is widely used in the analysis of crystallization kinetic data. Unfortunately, the use of the original model has been abandoned in favor of modified versions. The modifications are largely arbitrary and create a dependence between the Avrami constant and the Avrami exponent. From a curve-fitting point of view, no advantages exist in using the modified over the original form of the Avrami model. The order of a polynomial fit to crystallization data is not equivalent to the Avrami exponent. The use of turbidity measurements for the quantitative characterization of crystallization kinetics is not valid.     

Crystallization kinetics of two polyesters with different main chain rigidity

The crystallization kinetics of two polyesters, poly(p-phenylene sebacate) (PPS) and poly(p-phenylene isophthalate) (PPI), have been investigated by DSC. The nonisothermal data indicate that the relative crystallization rate of PPI was slower than that of PPS due to the more rigid nature of the PPI the chains. The isothermal crystallization data were analyzed by the Avrami equation, 1 − X_(t) = exp(−ktⁿ). PPS exhibited Avrami exponent (n), values of about 4, indicating that its isothermal crystallization followed a process of homogeneous nucleation, spherical growth and a growth type of interface control. PPI exhibited Avrami exponent values of about 3 indicating its isothermal crystallization followed a process of homogeneous nucleation, a possible disc growth geometry and an interface control growth type. Possibly, the bending structure and rigid nature of PPI forced its growth to follow a three dimensional growth during crystallization.     

聚乳酸切片及纤维的性能探讨

利用解偏振法测定了1#-4# PLA切片的等温结晶动力学,求解了PLA切片的Avrami指数n;用X射线衍射法测定了等温结晶后PLA切片样品及纤维的结晶度,测试了PLA纤维的力学性能。结果表明：PLA切片等温结晶动力学参数Avrami指数n在1.29～2.16之间,且4#〉3#〉2#〉1#;各批PLA切片等温结晶后的结晶度顺序与各批PLA纤维结晶度的顺序相一致;PLA纤维的强力随结晶度的增加而增加。     

Crystallization behavior of Bi1.25Y1.75Fe5O12 prepared by coprecipitation process

A non-isothermal study of the crystallization kinetic of coprecipitation of Bi_1.25Y_1.75Fe₅O₁₂ was carried out by differential scanning calorimetry (DSC). The Avrami exponent n suggesting the dimensionality of crystal growth was determined using the Ozawa equation. From non-isothermal DSC data presented values in range of 775–1023 kJ/mol and 3.28–2.10 for the activation energy of crystallization and the Avrami exponent, respectively. These Avrami exponent values were consistent with surface and internal crystallizations growth simultaneously.     

Application of the parallel Avrami model to crystallization of poly(etheretherketone)

We have reexamined the parallel Avrami model recently proposed by Velisaris and Seferis (1) to describe the non-Isothermal crystallization of poly(etheretherketone), PEEK. We show that, based on considerations of morphology development, the crystallization process with the larger Avrami exponent has the higher melting point, whereas the process with the smaller Avrami exponent has the lower melting point. This assignment differs from that of Velisaris and Seferis. In addition, we have used the infinite crystal melting point, as required by crystallization theory, to determine the Avrami rate parameters for the two processes. With this revision of the parallel Avrami model, we have applied the model to non-isothermal crystallization of APC-2 PEEK composite. Under the assumption that the linear growth rate determines the Avrami rate parameter, both the transport activation energy, U, and the kinetic parameter, K_g, are found to compare favorably with the values previously determined from isothermal crystallization of neat resin PEEK.     

SEBS-g-MAH对聚乙烯等温及非等温结晶动力学的影响

利用差示扫描量热法结合Avrami方程研究了苯乙烯-乙烯-丁烯-苯乙烯嵌段共聚物接枝马来酸酐(SEBS-g-MAH)对线型低密度聚乙烯(LLDPE)等温及非等温结晶动力学的影响。结果表明,热塑性弹性体SEBS及其接枝物的加入阻碍了LLDPE分子链的规则排列,影响了链段在结晶扩散迁移规整排列的速度,使得结晶速率变慢,对LLDPE晶体生长起了抑制作用;LLDPE/SEBS-g-MAH共混体系的半结晶时间t1/2和结晶活化能E明显增大,Avrami指数n对结晶温度有依赖性,kn值随温度的升高而减小。通过Jeziorny法对非等温结晶过程进行处理,试样的Avrami指数n值均在1.1~1.5,表明LLDPE的结晶成核机理和生长方式没有改变。     

Kinetics of non-isothermal cold crystallization of uniaxially oriented poly(ethylene terephthalate)

The non-isothermal equation was extended to describe non-isothermal cold crystallization kinetics of oriented polymers. The validity of the equation was examined by using a DSC crystallization curve of oriented poly(ethylene terephthalate) (PET) fibers with a constant heating rate. The double cold crystallization peaks appeared in the DSC curve. The relative degrees of crystallinity at different temperatures were analyzed by using the equation. The results show that the value of the Avrami exponent near to 1 at lower temperatures implies the bundle-like crystal growth geometry and the value of the Avrami exponent near to, 2, at higher temperatures implies the higher dimension crystal growth geometry. The first crystallization process crystallizes at faster rate than that of the isotropic sample, while the second process crystallizes at slower rate than that of isotropic sample. If a simple single process model was used, the value of the Avrami exponent, 0.77, was obtained. The result shows the simple single process model cannot describe the processes of crystallization of oriented PET fibers satisfactorily.