甘蔗渣对聚甲基丙烯酸甲酯热降解的影响

目的分析生物质材料对塑料废弃物热降解的影响,以聚甲基丙烯酸甲酯(PMMA)为对象,探讨甘蔗渣对其热分解行为和动力学的作用。方法利用溶液共混法制备PMMA/甘蔗渣混合物,采用热失重法研究其在氮气中的热分解过程,通过最大失重速率法和Ozawa等失重法计算PMMA热分解反应的动力学参数活化能和频率因子。结果甘蔗渣使得PMMA的初期热分解温度明显降低,但是PMMA的热分解活化能和频率因子却都显著增加。最大失重速率法的计算结果表明,PMMA加入甘蔗渣后的热分解活化能增加了26.2 k J/mol,等失重法的结果显示活化能和频率因子分别为168.14 k J/mol和28.41 min-1,比纯PMMA相应地增大了72.6 k J/mol和12.52 min-1。结论甘蔗渣的加入对PMMA的热降解有显著的影响,使其热分解变得困难,因此有必要进一步探讨其他生物质对PMMA热分解的影响。     

不同碳黑含量PMMA的热降解行为和动力学分析

用熔融共混法制备不同碳黑(CB)含量的聚甲基丙烯酸甲酯(PMMA)材料,根据固态反应动力学研究了这种材料的热降解行为。在不同升温速率的非等温热重分析(TGA)实验的基础上用Friedman、FWO、KAS和Freeman-Carroll四种方法构建了不同碳黑含量PMMA的热降解动力学模型,并将TGA实验数据与求解模型对比验证了模型的可靠性。结果表明：添加碳黑使PMMA的热分解温度和活化能提高,碳黑含量(质量分数)为0.1%时达到峰值;随着碳黑含量的提高PMMA的活化能先增大后减小,其最大提高量为17.76 kJ·mol^-1,表明加入碳黑能在一定程度上提高PMMA的热稳定性。     

含新型发色团的非线性光学聚合物体系的热性能研究

分别对掺杂了新型发色团分子的聚甲基丙烯酸甲酯(PMMA)和纯的PMMA进行了热重分析,得到了2种体系在不同质量损失下的温度并计算了积分程序分解温度(IPDT).结果表明,掺杂后聚合物体系的热稳定性好于纯的PMMA.采用Achar方法和Coats-Redfern方法对2种体系热降解的动力学过程进行了分析,得到了对应的非等温动力学方程.     

煤粉/聚氯乙烯共混体系的热稳定性

采用熔融共混法制备了煤粉/聚氯乙烯(PVC)复合材料,利用热重分析研究了质量分数为5%、10%、15%煤粉含量对PVC在高纯度氩气中的热稳定性影响。通过Kissinger方法研究其热降解动力学,计算其热降解表观活化能(Ea),并利用扫描电镜对复合材料的断口进行分析。结果表明,共混体系的热降解过程表现为2个失重阶段,煤粉对PVC第一阶段热降解活化能影响不大,但提高了第二阶段热降解活化能。在煤粉加入质量分数为10%时,第二阶段Ea达到了最大值218.7kJ/mol,较纯PVC提高了58.5kJ/mol。通过复合材料的断口扫描电镜照片发现,共混体系的热稳定性与煤粉的含量和分布有关。     

煤粉/聚氯乙烯共混体系的热稳定性EI北大核心CSCD

采用熔融共混法制备了煤粉/聚氯乙烯(PVC)复合材料,利用热重分析研究了质量分数为5%、10%、15%煤粉含量对PVC在高纯度氩气中的热稳定性影响。通过Kissinger方法研究其热降解动力学,计算其热降解表观活化能(Ea),并利用扫描电镜对复合材料的断口进行分析。结果表明,共混体系的热降解过程表现为2个失重阶段,煤粉对PVC第一阶段热降解活化能影响不大,但提高了第二阶段热降解活化能。在煤粉加入质量分数为10%时,第二阶段Ea达到了最大值218.7kJ/mol,较纯PVC提高了58.5kJ/mol。通过复合材料的断口扫描电镜照片发现,共混体系的热稳定性与煤粉的含量和分布有关。     

D,L-聚乳酸热降解动力学研究

通过热重分析研究了D,L-聚乳酸(PDLLA)在N2气氛中,不同升温速率条件下的热降解过程及其动力学行为.结果表明,PDLLA的主热降解过程为一级反应,当温度超过250℃时即发生明显降解,同时分别利用Ozawa-Flynn-Wall、Friedman和Freeman-Carroll方法对其动力学参数进行了测定,得到PDLLA的热降解活化能值为97.78kJ/mol.     

主链含苯基均三嗪联苯型聚芳醚的热稳定性

利用热重分析(TG、DTG)研究了主链含苯基均三嗪联苯型聚芳醚在不同气氛和升温速率时的热降解动力学。比较了升温速率和气体气氛对热降解行为的影响,结果表明,该聚合物具有优异的耐热性和耐热氧化稳定性。用Flynn-Wall-Ozawa,Freeman-carroll等方法进行了动力学处理,计算得热降解反应活化能分别为291.19kJ/mol,286.83kJ/mol,与Kissinger法计算活化能值283.25kJ/mol非常接近。结合Coats-Redfern方法,推测出聚合物在氮气气氛中的热分解机理为F2机理,其机理函数积分式为g(α)=1/(1-α)。     

水热反应温度对PMMA/TiO_2复合纳米纤维膜的形貌和性能的影响

利用静电纺丝技术成功制备了聚甲基丙烯酸甲酯/钛酸四正丁酯(PMMA/TBT)复合纳米纤维膜,通过水热法处理得到了PMMA/TiO_2柔性复合纳米纤维膜。通过傅立叶红外光谱(FTIR)、热失重分析法(TGA)、X射线衍射法(XRD)等手段对PMMA/TiO_2复合纳米纤维膜进行了表征,借助扫描电子显微镜(SEM)、全自动比表面积及孔隙分析仪(BET)对该材料的形貌结构、孔隙结构进行分析,最后探讨了所制备的纳米纤维膜的光催化降解能力,综合分析了反应温度对水热法制备PMMA/TiO_2复合纳米纤维膜的形貌、结构及性能的影响。结果表明:水热反应温度为200℃时,得到的PMMA/TiO_2复合纳米纤维膜中TiO_2晶型为纯锐钛矿型,且晶体生长速率较快,比表面积较大,对污染物亚甲基蓝的脱色效率最高,可达98.93%。     

柔性PMMA/TiO_2复合超细纤维的制备及表征

利用静电纺丝技术制备出聚甲基丙烯酸甲酯/钛酸四正丁酯(PMMA/TBT)复合超细纤维膜,并通过水热法处理得到PMMA/TiO_2柔性复合纳米纤维膜。通过傅里叶红外光谱(FT-IR)、热失重分析法(TGA)、X射线衍射法(XRD)等手段对PMMA/TiO_2复合纳米纤维膜进行表征,借助扫描电子显微镜(SEM)、全自动比表面积及孔隙分析仪(BET)对该材料的形貌结构、孔隙结构进行分析,最后探讨了所制备的纳米纤维膜的光催化降解能力,综合分析了pH值对水热法制备PMMA/TiO_2复合纳米纤维膜的形貌、结构及性能的影响。结果表明,成功制备出了比表面积较大,催化活性较高的PMMA/TiO_2复合纳米纤维膜;在水热反应过程中pH=8时,得到的PMMA/TiO_2复合纳米纤维膜中TiO_2晶型为锐钛矿型,且比表面积较大,对拟污染物亚甲基蓝的脱色率达到95%。     

聚丙撑碳酸酯/聚苯乙烯复合材料的制备与性能

利用熔融共混的方法制备了聚丙撑碳酸酯/聚苯乙烯(PPC/PS)复合材料,并通过万能试验机、差示扫描量热分析仪(DSC)、热重分析仪(TG)以及扫描电子显微镜(SEM)分别研究了复合材料的力学性能、热性能及微观形态.结果表明,PS的引入提高了复合材料的拉伸强度和拉伸模量及热稳定性,对体系中两相的玻璃化转变温度也有一定的影响.因此,通过简单的熔融共混的方法制备PPC/PS复合材料,可达到对PPC增强改性的目的,且大大降低了PPC的应用成本,对PPC的工业化应用提供了一条新的途径.     

iCVD growth of poly(N-vinylimidazole) and poly(N-vinylimidazole-co-N-vinylpyrrolidone)

The imidazole group plays an important role in α-chymotrypsin catalysis, metal-ion complexation, counterion or dye binding. Poly(N-vinylimidazole), PVI, is also a good model polymer interacting with neutral salts. The poly(N-vinylimidazole-co-N-vinylpyrrolidone) copolymer P(VI-co-VP), can be used to produce highly functionalized polymers.PVI and P(VI-co-VP) thins films were achieved via initiated chemical vapor deposition (iCVD), a solvent-free process to form films under mild conditions. The polymerization was initiated by hot wire heated tert-butyl peroxide (TBPO). The chemical structure and compositions of the polymers were analyzed using FTIR and XPS. The growth rate of PVI as a function of the pressure inside the iCVD reactor was measured to be 1 nm/h mTorr. The XPS results show that the functional groups were retained in the polymer deposited. For the P(VI-co-VP) deposition, there are more VI groups found in the co-polymer chain even when the reacting monomers were fed in the same ratio.     

Polymeric nanomedicines based on poly(lactide) and poly(lactide-co-glycolide)

Small molecule chemotherapeutics often have undesired physiochemical and pharmacological properties, such as low solubility, severe side effect and narrow therapeutic index. To address these challenges, polymeric nanomedicine drug delivery technology has been routinely employed, in particular with the use of biodegradable and biocompatible polyesters, such as poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA). Here we review the development and use of PLA and PLGA for the delivery of chemotherapeutic agents in the forms of polymer–drug conjugates and nanoconjugates.     

Reinforcement of elastomeric poly(dimethylsiloxane) by glassy poly(diphenylsiloxane)

Some novel approaches were taken to provide the improvements in mechanical properties that are almost always necessary to prepare a commercially useful elastomer from poly(dimethylsiloxane) (PDMS) [-Si(CH₃)₂O-]. The reinforcement was provided by poly(diphenylsiloxane) (PDPS) [-Si(C₆H₅)₂O-], a hard glassy polymer, which was introduced into the PDMS by two rather different techniques. In the first, the PDPS was prepared separately by condensation polymerization of diphenylsilanediol and then solution-blended into the PDMS. In the second, it was generated by in situ polymerization of the same monomer absorbed into the PDMS network. The resulting materials were characterized by scanning electron microscopy and by stress-strain isotherms in elongation. At least under some conditions both techniques were found to be successful, leading to increases in ultimate strength by a factor of two or more.     

聚乙二醇改性聚乳酸的合成与性能表征

以外消旋乳酸(D,L-LA)和不同数均分子量(Mn)的聚乙二醇(PEG)为原料,通过熔融缩聚法,合成了系列聚乳酸聚乙二醇(PLEG)。最佳工艺条件为:以(Sn(Oct)2)为催化剂,m(Sn(Oct)2)为0.8%,n(PEG)∶n(D,L-LA)=1∶600,聚合温度170℃,压力0.096 MPa条件下,反应8h。用特性粘度测试、FT-IR、XRD、接触角等对其进行表征,实验结果表明系列PLEG中PLEG-800接触角为63°,表明其亲水性能最好;PEG-800和乳酸共聚合成的PLEG的粘均分子量最大,可达48997,与PDLLA相比,结晶度有较大提高,亲水性得到改善。     

Plasma surface treatments of poly(l-lactic acid) (PLLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)

The surfaces of poly(l-lactic acid) (PLLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) were modified by oxygen and nitrogen plasma treatments. The physical and chemical surface characteristics were evaluated by contact angle tests, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The plasma treatments caused an increase in both contact angle and roughening, altered the surface morphology, inserted polar groups, and, consequently, enhanced the hydrophilicity for both PLLA and PHBV polymers.     

Interphase transfer of tackifier between poly(butadiene) and poly(styrene-co-butadiene)

The interphase transfer behavior of poly(styrene-co-α-methyl styrene), which is known as a tackifier in rubber industry, is investigated using poly(butadiene) rubber (BR) and poly(styrene-co-butadiene) rubber (SBR). The films of pure rubbers and the blends with the tackifier were prepared by a solution-cast method using toluene as a solvent. Two sheets composed of different rubbers, in which the tackifier was mixed at least in one rubber sheet, were piled together and annealed beyond the glass transition temperature T _g of the tackifier. The transfer phenomenon of the tackifier between the sheets was evaluated by the peak shift in the tensile loss modulus E″ curve, ascribed to T _g of the rubbers, which was measured by the dynamic mechanical analysis. Moreover, crystallization temperature of BR was also employed as a measure of the transfer, because the tackifier retards the crystallization of BR. It is found that the tackifier moves from one rubber to another during annealing procedure to reduce severe localization. When the content is the same in each rubber, the tackifier immigrates from BR to SBR, suggesting a better miscibility with SBR. This behavior is attributed to the small difference in the solubility parameter between SBR and the tackifier as compared to that between BR and the tackifier.     

Properties of magnetic poly(glycidyl methacrylate) and poly(N-isopropylacrylamide) microspheres

Iron oxide colloids were prepared by coprecipitation of Fe(II) and Fe(III) salts in alkaline media and stabilized by perchloric acid, oleic acid, or poly(acrylic acid). In an attempt to obtain magnetic polymer microspheres differing in size, dispersion polymerization of glycidyl methacrylate (GMA) in ethanol containing HClO₄-stabilized magnetite, dispersion copolymerization of GMA and 2-hydroxyethyl methacrylate (HEMA) in toluene/2-methylpropan-1-ol mixture in the presence of oleic acid-coated magnetite, and inverse suspension copolymerization of N-isopropylacrylamide (NIPAAm) and N,N′-methylenebisacrylamide (MBAAm) in cyclohexane in the presence of poly(acrylic acid)-coated maghemite were compared. The microspheres were characterized by morphology, size, polydispersity, and some magnetic properties.     

Environmentally-affected indentation fracture in poly(ethersulphone) and poly(methyl methacrylate)

The effect of plasticization on the ductile-to-brittle fracture transitions (DBFT) in the ball indentation of poly (ethersulphone) (PES) and poly(methyl methacrylate) (PMMA) has been studied. The DBFT in various organic liquids are governed by a size effect related to the indenter radius, in accordance with the Puttick theory of fracture transitions. In addition, abrasive wear rates of the polymers in these liquids are shown to correlate with the critical indenter radius needed to produce a fracture transition, owing to the connection with fracture toughness.     

NMR analysis of poly(ethylene naphthalate) + poly(butylene terephthalate) blends

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. ¹³C and ¹H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in ¹H and ¹³C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases.