蒙脱石有机化对PVA/蒙脱石复合薄膜的性能影响

以精制钠基蒙脱石(Na-MMT)、有机化蒙脱石(OMMT)和聚乙烯醇(PVA)为原料,通过水溶液插层-流延成膜法制备纳米复合薄膜。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和热重分析(TGA)对复合材料的结构和性能进行表征,重点探讨蒙脱石有机化对PVA/MMT复合薄膜性能的影响。结果表明Na-MMT和OMMT纳米颗粒在PVA基体中均得到了良好分散;有机改性剂的存在促使PVA/MMT复合薄膜的MMT片层间距扩撑更大,但由于其与PVA相容性较差,导致有效插入MMT片层间的PVA分子较少,PVA/MMT复合薄膜的热稳定性改善效果不明显。     

熔融插层法制备聚乳酸/蒙脱土纳米复合材料的研究进展

综述了使用熔融插层法制备聚乳酸（PLA）/蒙脱土（MMT）纳米复合材料及其表征与性能的研究进展。研究表明,对MMT进行有机改性,可以增大MMT片层间距,使PLA/MMT形成剥离和插层的结构,同时有效地提高PLA/MMT复合材料的性能。随着MMT含量的增加,MMT片层粒子容易形成团簇,不利于结构分散以及性能提高;由于MMT片层粒子在PLA基体中良好分散,形成剥离/插层的结构,有利于抑制PLA分子链运动,从而提高了PLA的韧性、热稳定性、气体阻透性能;MMT片层粒子作为二维异向成核剂,可以提高复合材料的结晶度和结晶速率;分散的MMT片层粒子形成了一种空间连接结构,大大提高了复合材料的熔体强度,有利于拓宽其加工窗口;同时MMT结构中的末端羟基可以增加复合材料的生物降解速率。     

再生PVDF/蒙脱土纳米复合材料制备与性能

通过新型非对称双螺杆挤出机制备再生聚偏氟乙烯(PVDF)/蒙脱土(MMT)纳米复合材料,采用傅里叶变换红外光谱仪、差示扫描量热仪、热重分析仪、扫描电子显微镜(SEM)、转矩流变仪和万能电子试验机等对材料进行表征测试,研究MMT含量对复合材料结构和性能的影响。结果表明,MMT对复合材料的结晶行为有一定的影响,添加MMT后复合材料的熔融温度、结晶温度和结晶度都有提高,添加1% MMT复合材料的熔融温度和结晶温度分别比未加MMT的再生PVDF提高1℃和0.94℃;再生PVDF/MMT复合材料的降解温度随着MMT含量增加而降低,失重50%的温度反而随MMT含量增加而升高;SEM发现,MMT以100～200 nm的片状分散在PVDF基体中,随着MMT含量增加,出现MMT团聚、脱落现象;在实验范围内,随着MMT含量的增加,复合材料的拉伸强度和缺口冲击强度随之提高,添加5% MMT复合材料的拉伸强度比未添加MMT的提高33.5%,缺口冲击强度提高29.7%;转矩流变实验发现,适量的MMT增加了复合材料加工时的剪切作用,降低了熔体塑化平衡扭矩。     

BU成核剂对聚乳酸结晶行为的影响研究

研究了有机成核剂(TP)、蒙脱土(MMT)以及TP/MMT复合体系对聚乳酸(PLA)的成核作用。采用差示扫描量热法(DSC)、偏光显微镜(POM)、X射线衍射(XRD)对PLA结晶行为进行表征分析。结果表明,在实验范围内,TP及MMT分别加入PLA基体中时,能有效地提高PLA的结晶度,结晶度较纯PLA提高了约9%;TP/MMT复合体系对PLA结晶行为的影响更显著,结晶度比纯PLA提高了13%左右,缩短结晶时间。TP、MMT及TP/MMT均不会改变PLA的晶型,但起到异相成核作用,促进PLA的结晶。     

制样方法对SiO2/PA6复合材料基体PA6结晶熔融行为的影响

采用差示扫描量热法(DSC)研究了原位聚合法和熔融共混法制样方法对纳米SiO2/PA6纳米复合材料结晶熔融行为的影响,结果表明:通过阴离子原位聚合法制备的纳米复合材料,由于采用超声波分散技术,纳米粒子在基体的分散性好。随着纳米粒子含量的升高,纳米粒子的诱导成核能力增强;熔融共混法制得复合材料中,SiO2在机械力的剪切作用下,很难均匀地分散,多以团聚体的形式存在,在PA6基体结晶时,结晶成核的条件相匹配,有较强的成核效应,纳米粒子的含量影响不大。     

多壁碳纳米管官能化对PVDF结晶行为的影响

采用溶液共混结合溶剂蒸发法制备了聚偏氟乙烯(PVDF)/多壁碳纳米管(MWCNTs)复合薄膜。研究了MWCNTs表面羟基化(MWCNTs-OH)、羧基化(MWCNTs-COOH)、氨基化(MWCNTs-NH_2)以及接枝聚甲基丙烯酸甲酯(PMMA)(MWCNTs-g-PMMA)后对PVDF结晶行为的影响。结果表明:官能化前后的MWCNTs均可提高PVDF的β晶型相含量,复合薄膜的熔融温度、结晶温度、结晶度和结晶速度均得到提高。其中含MWCNTs-g-PMMA的复合薄膜中β相含量最高,晶核密度最大,晶体尺寸较小,而结晶度有所降低,但总体都高于纯PVDF;由于MWCNTs-NH_2的氨基与PVDF分子链之间的相互偶极作用和氢键协同影响,对PVDF的结晶促进作用最为明显。     

苯甲酸钠/层状填料复合成核体系对聚丙烯结晶性能的影响

将苯甲酸钠(SB)成核剂负载到云母(Mica)和蒙脱土(MMT)表面,考察两种复合成核体系对聚丙烯(PP)结晶性能的影响.结果表明:SB分别与Mica和MMT有协同成核作用,负载处理后成核剂能够较好地分散在体系中,起到良好的成核作用,使得结晶峰温度和结晶速率提高,同时大大地减小了晶体尺寸,有较好的成核效率.但是填料的尺寸对负载效果没有太大的影响.     

PVDF/PLLA共混体系的结晶行为和球晶生长形貌研究

通过溶液浇铸共混法制备聚偏氟乙烯(PVDF)/聚左旋乳酸(PLLA)共混物,采用傅里叶变换红外光谱仪(FTIR)、偏光显微镜(POM)以及差示扫描量热仪(DSC)研究共混物的晶体生长形貌和熔融结晶行为。结果表明:PLLA对PVDF的球晶生长有明显的阻碍作用,当PLLA质量分数达到80%时完全抑制了PVDF的结晶。共混物中PVDF晶体的生长方式随PLLA含量的增多,由原来的三维球状生长变为三维和二维生长并存。相反,少量的PVDF却有促进PLLA成核、结晶的作用,尤其当PVDF质量分数低于20%时,PLLA的结晶时间大幅缩短,结晶起始温度也显著提高。     

聚氧乙烯薄膜的结晶形态研究

以不同相对分子质量的聚氧乙烯(PEO)为研究对象,采用差示扫描量热仪、偏光显微镜和原子力显微镜研究了影响PEO薄膜结晶的主要因素。结果表明:影响PEO结晶的主要因素是结晶温度,PEO在25℃形成球晶,温度升高时,晶体尺寸亦略微增加,黑十字消光现象明显,且可观察到环形裂纹;结晶温度较低时,片晶生长先由成核生长机理控制,而后由扩散生长机理控制,结晶温度较高时,片晶生长主要由成核机理控制;相对分子质量对晶体尺寸有一定影响,但不影响结晶形态,随着相对分子质量的增加,PEO薄膜的片晶形成由成核机理控制转变成扩散机理控制,PEO晶体从Flat-on结构逐渐转变为Edge-on结构。     

聚氧乙烯超薄膜等温结晶过程的研究

利用原子力显微镜(AFM)研究了不同温度的聚氧乙烯(PEO)超薄膜等温结晶过程。结果表明:超薄膜晶体形貌具有生长控制因素的依赖性;当晶体生长同时受到表面成核和熔体扩散控制时,各方向生长速率明显不同,且在晶体形成过程中,先发生液相-固相转变,后发生固相-固相转变。     

Formation of an interconnected lamellar structure in PVDF membranes with nanoparticles addition via solid‐liquid thermally induced phase separation

Novel microporous membranes were prepared via thermally induced solid‐liquid (S‐L) phase separation of mixtures containing poly(vinylidene fluoride) (PVDF)/diphenyl ketone (DPK)/nanoparticles [such as montmorillonite (MMT) and polytetrafluoroethylene (PTFE)] in diluted systems with a mass ratio of 29.7/70/0.3 wt %. The crystallization and melting characteristics of these diluted systems were investigated by polarizing optical microscopy (POM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and wide angle X‐ray diffraction (WAXD). The nanoparticle structure and the interaction between PVDF chains and nanoparticle surfaces determined the crystallization behavior and morphology of the PVDF membrane. The addition of MMT and PTFE had a significant nucleation enhancement on the crystallization of PVDF accompanied by S‐L phase separation during the thermally induced phase separation (TIPS) process. It was observed that an interconnected lamellar structure was formed in these two membranes, leading to a higher tensile strength compared with that of the reference membrane without nanoparticles addition. Additionally, addition of MMT facilitates the fiber‐like β phase crystal formation, resulting in the highest elongation at break. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crystallization behavior of poly(vinylidene fluoride)/montmorillonite nanocomposite

The crystallization behavior of poly(vinylidene fluoride)/montmorillonite (PVDF/MMT) nanocomposite was investigated by using differential scanning calorimeter (DSC), polarizing optical microscope (POM), and X‐ray diffraction. The results showed that the crystallization behavior of PVDF was changed by adding MMT in PVDF matrix. The MMT layers in PVDF acted as effective nucleation agents. It is observed that the crystallization temperature of PVDF/MMT nanocomposite was higher than that of PVDF at various cooling rates. The value of half‐time of crystallization showed that the crystallization rate of PVDF/MMT nanocomposite was faster than that of PVDF at a given cooling rate. The addition of MMT hindered the growth of spherulite. Nonisothermal crystallization data was analyzed using Avrami, Ozawa, and Jeziorny method. The Jeziorny method successfully described the nonisothermal crystallization behaviors of PVDF/MMT nanocomposite. The MMT loading was favorable to produce the piezoelectric β phase in the PVDF matrix. The α phase coexisted with the β phase in the PVDF/MMT nanocomposite. For this polymorphic structure, a possible explanation was proposed based on the variable temperature X‐ray diffraction, DSC, and POM experiments. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Increasing solvent polarity and addition of salts promote β‐phase poly(vinylidene fluoride) formation

This article investigates the effects of solvent polarity and salt addition on β‐phase poly(vinylidene fluoride) (PVDF) formation. Films were solvent cast in aprotic solvents of varying polarities with or without salt addition. Characterization was done by Fourier transformed infra‐red spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Decreasing fractions of β‐phase PVDF was observed with increasing drying temperature when less polar solvents were used. The most polar solvent (hexamethylphosphoramide) consistently produced films with at least 90.0% β‐phase PVDF within the crystalline regions. Melting temperatures increased in correlation to absolute proportions of β‐phase PVDF. Salt addition increased the formation of β‐phase PVDF by 30%, with salts of higher valencies and smaller ionic radii resulting in more significant increases. Taken collectively, using solvents of higher polarities and addition of salts with high cationic valencies and small ionic radii will maximize β‐phase formation in solvent cast PVDF films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

四苯基氯化鏻对聚偏氟乙烯电活性相的诱导作用

通过简单的熔体共混方法,将不同质量分数的高熔点高活性的四苯基氯化鏻(TPPC)与聚偏氟乙烯(PVDF)混合,探究了TPPC对PVDF极性相的诱导作用,并研究了此体系与熔体结晶过程最为相近的非等温结晶过程。结果表明,添加极少量(0.4%)的TPPC即可以使PVDF直接从熔体中全部以极性相结晶,这归因于TPPC固体表面的电荷与PVDF分子链之间强烈的相互作用。TPPC的加入使PVDF的非等温结晶行为发生了很大的变化,当TPPC含量达到0.4%时,降温结晶曲线出现两个结晶峰,也是这种反常的结晶行为才能使PVDF几乎全部以极性相结晶。     

Membrane formation of poly(vinylidene fluoride)/poly(methyl methacrylate)/diluents via thermally induced phase separation

The role of the single diluents and mixed diluents on the poly (vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend membranes via thermally induced phase separation (TIPS) process was investigated. The crystallization behaviors of PVDF in the diluted samples were examined by differential scanning calorimetry. The melting and crystallization temperatures of those diluted PVDF blend were decreased with the enhanced interactions between polymer chains and diluent molecules. The crystallinity of PVDF in the diluent was always higher than that obtained in PVDF blend sample. This can be explained by the dilution effects, which increased the average spatial separation distances between crystallizable chains. Thus, the PVDF crystallization was favored. Additionally, solid‐liquid (S‐L) phase separation occurred in the quenched samples. Illustrated by scanning electron microscopy, inter‐ and intraspherulitic voids were formed in the ultimate membranes, which related to the polymer/diluent interactions, the kinetics of crystallization and diluent rejection from the growing crystal. The porosity of the PVDF blend membranes obtained from the mixed diluents was higher than those obtained from the single diluent samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on heterogeneous nucleation effect of dispersing intercalated montmorillonite clay platelets in polyaniline matrix

In this article, a series of nanocomposite materials that consisted of emeraldine base (EB) of polyaniline (PANI) and montmorillonite (MMT) clay were prepared by effectively dispersing the inorganic MMT clay platelets into organic PANI matrix via in situ chemically oxidative polymerization. Organic aniline monomers were first intercalated into the interlayer regions of organophilic clay hosts and followed by an one‐step oxidative polymerization with ammonium persulfate as oxidant. The as‐synthesized PANI‐clay nanocomposite (PCN) materials were characterized by Fourier‐Transformation infrared spectroscopy and transmission electron microscopy. It should be noted that the EB of PANI in the presence of dispersed intercalated MMT clay platelets was found to display an observable enhancement in polymer crystallinity as compared with that of neat PANI based on series of investigations of wide‐angle powder X‐ray diffraction patterns and differential scanning calorimetric studies. This remarkable increase of polymer crystallinity might be resulted from the effective heterogeneous nucleation effect of dispersed clay platelets existed in PCN materials. The surface morphology study of PCN materials was further evaluated by polarizing optical microscopy, scanning electron microscopy, and atomic force microscopy. POLYM. COMPOS., 31:2049–2056, 2010. © 2010 Society of Plastics Engineers     

Phase transformation mechanisms and piezoelectric properties of poly(vinylidene fluoride)/montmorillonite composite

Poly(vinylidene fluoride) (PVDF)/montmorillonite (MMT) composite with different MMT contents were prepared by solutions‐casting method. The effects of MMT on crystalline structure, morphology, dielectric property, piezoelectric property and phase transformation mechanism were studied. The results showed that acted as effective nucleation agents, the orientation of MMT were almost parallel to the surface of the film. The beta phase in the PVDF matrix was increased and the alpha phase was decreased. Relative dielectric constant and loss of the composite were increased with the increasing of MMT. The d₃₃ was also increased with MMT, which reached a maximum (5.8pC/N) with 2.0 wt % MMT. The mechanisms of changes in phase transformation and piezoelectric property were proposed based on experiment results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology,polymorphism, and metal ion adsorption studies of electrospun nanofibers based on PVDF and organically modified layered double hydroxide

Nonwoven nanofiber mats of polyvinylidene fluoride (PVDF) with modified layered double hydroxide (MLDH) were prepared by electrospinning. The fiber morphology was studied using scanning electron microscopy. X‐ray diffraction and FTIR spectroscopy was used to characterize the polymorphism in electrospun mats. Fibers of diameter in the range 80–800 nm with beads of about 2–3 µm size were observed for pure PVDF, while in case of PVDF/MLDH nanocomposites the number and size of beads were found to be significantly reduced. Uniform and fine nanofibers were obtained at lower content of MLDH, but slightly rough surface was seen for higher content. FTIR and X‐ray diffraction patterns signify various crystalline forms of electrospun PVDF. The content of polar β‐crystalline phase of PVDF, which exhibit piezo and ferroelectric properties was found to be enhanced significantly due to reinforcement of MLDH. Use of these nanofiber mats for heavy metal Cu (II) removal was explored. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4508–4515, 2013     

Compatibilization of PVDF/PA6 Blend by the Addition of a Third Polymer PTFE

The compatibilization of poly(vinylidene fluoride) (PVDF) with polyamide 6(PA6, higher acrylonitrile content) blend was improved by adding poly(methyl methacrylate) (PTFE). It was confirmed by characterizing the mechanical and tribological properties of the blends. More homogeneous morphology was formed when PTFE was added into PVDF/PA6 blend, which was shown in scanning electron microscopy (SEM). The surface tension of blends was increased due to the higher polar surface tension of PTFE. As the content of PTFE was increased further, the tensile strength of the blend was slightly decreased.     

Effect of solvents on morphology and polymorphism of polyvinylidene fluoride membrane via supercritical CO2 induced phase separation

Poly vinylidene fluoride (PVDF) membranes were prepared via supercritical CO₂ induced phase separation. The effects of solvent power on PVDF membrane morphology and polymorphism were investigated using N‐N‐dimethylformamide (DMF), triethyl phosphate (TEP), and their mixture respectively. The morphology evolution including cross‐section and surfaces were thoroughly studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). The differences of solubility parameters between the solvent and PVDF affected the phase separation and the resultant morphology. The various crystalline phases of the membranes were mainly investigated by Fourier transform infrared spectroscopy (FTIR) and X‐ray diffractometer (XRD). Solvent with larger dipole moment tended to form polar β phase. Decreasing the difference of solubility parameters favored the formation of α phase. Furthermore, the effects of salt additive on PVDF membrane morphology and crystalline form were studied as well. Results turned out that lithium chloride (LiCl) induced a porous top surface and boosted the formation of β phase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41065.