固相剪切碾磨制备聚丙烯/废旧橡胶/聚烯烃弹性体复合材料

利用固相剪切碾磨技术在常温下制备了聚丙烯(PP)/废旧轮胎橡胶(GTR)/聚烯烃弹性体(POE)复合材料。采用力学性能测试、差热分析(DSC)和扫描电镜(SEM)对固相剪切碾磨制备的GTR/POE复合粉体和相应PP/GTR/POE复合材料进行表征和分析,研究了碾磨次数和GTR/POE含量对PP/GTR/POE复合材料结构与性能的影响。结果表明,对固相剪切碾磨方法制备的PP/GTR/POE复合材料,GTR和POE被有效粉碎和均匀分散,其冲击强度和断裂伸长率比常规熔融共混方法制备的复合材料高;增加GTR/POE共碾磨复合粉体的含量或增加碾磨次数均可提高冲击强度和断裂伸长率。     

纳米高岭土的固相剪切碾磨制备及对PVC的增强增韧

采用固相剪切碾磨方法成功制备了聚氯乙烯(PVC)-高岭土复合粉体,实现了高岭土的片层剥离和在PVC基体中的纳米分散及对PVC的同步增强增韧。通过X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)表征了PVC-高岭土纳米复合材料的结构,研究了其力学性能。结果表明,30次碾磨,高岭土的特征衍射峰几乎消失,高岭土以约30 nm片层厚度均匀分散于PVC基体,径厚比超过10。与简单填充复合方法相比,固相剪切碾磨技术制备的PVC/高岭土纳米复合材料的力学性能有较大提高。在高岭土质量分数为4%时,断裂伸长率由87.3%提高到274.6%,提高了214.7%;拉伸强度由47.7 MPa提高到54.0 MPa。     

高β相离子液体/聚偏氟乙烯介电材料及熔融沉积成型

通过将聚偏氟乙烯(PVDF)与离子液体(IL)熔融共混制备IL/PVDF复合材料，并研究其晶相结构。结果表明，离子液体的咪唑阳离子与PVDF的-CF₂基团之间的相互作用能够有效诱导PVDF极性β相的生成，复合材料的β相相对含量最高可达81.83%,是纯PVDF的2.7倍。IL/PVDF复合材料的介电常数最高可达21.0(100 Hz),相比纯PVDF提高了4倍。此外，探讨了熔融沉积成型(FDM)对IL/PVDF复合材料的影响，发现FDM成型能够进一步提升复合材料的极性β相含量X_c(β),这对FDM成型制备PVDF基电子储能及传感设备具有一定的参考价值。     

固相剪切碾磨制备尼龙12/多壁碳纳米管复合粉体及选择性激光烧结3D打印

采用固相剪切碾磨(S~3M)技术并结合冷冻粉碎制备了适于选择性激光烧结(SLS)的尼龙12(PA12)/多壁碳纳米管(CNTs)复合粉体及相应的烧结制品。采用激光粒度分析仪、扫描电镜、透射电镜、动态力学分析、傅里叶变换红外光谱分析、差示扫描量热仪等对所得PA12/CNTs复合粉体和相应SLS制品的结构与性能进行了表征。结果表明,固相剪切碾磨-冷冻粉碎制备的复合粉体颗粒以椭球形为主,平均粒径75μm,SLS加工窗口为10℃左右,满足SLS对被烧结材料的性能要求,通过加入质量分数为0.1%的流动助剂纳米SiO_2能进一步改善复合粉体的SLS加工性能。磨盘碾磨通过其强大的三维剪切力场实现了CNTs的切割及在PA12基体中的良好分散以及CNTs与PA12大分子链的接枝,显著改善了二者之间的界面相容性。此外,通过优化SLS加工参数,成功制备了表面平整、结构复杂、性能良好的PA12/CNTs烧结制品。所得PA12/CNTs烧结样品具有优良的力学性能,拉伸强度达到44.2 MPa,缺口冲击强度达到8.12 k J/m~2。     

PVDF铁电聚合物薄膜的溶液法制备

采用溶液流延法制备了β相聚偏二氟乙烯(PVDF)铁电聚合物薄膜,研究了不同热处理条件和不同溶剂对薄膜晶相结构形成的影响.利用X射线衍射仪、傅立叶红外光谱仪(FTIR)对晶形结构进行了分析.结果表明,在合适的温度条件下,基片的热诱导作用有利于β晶相形成,而在较高温度下主要形成γ晶相,较低的温度将会抑制PVDF结晶;溶剂的溶度性能对薄膜的结晶能力和晶型的形成有很大影响,采用对PVDF溶解能力较强的溶剂DMSO所制备的薄膜中晶区内β晶型的含量高但其结晶能力差,而采用溶解能力较弱的DMAc溶剂虽然提高了薄膜的结晶度,却降低了β晶型的含量.     

拉伸工艺对聚偏氟乙烯薄膜结晶特性的影响

采用挤出法制备了PVDF片材;利用单轴拉伸工艺制备了β相含量相对较高的聚偏氟乙烯(PVDF)薄膜;采用偏光显微镜、差示扫描测试仪、X射线衍射仪等仪器,分析了拉伸过程中PVDF薄膜的形貌、结晶度以及结构变化,讨论了不同拉伸温度、不同拉伸比以及不同拉伸速率对薄膜微观结构及β相相对含量的影响。结果表明:PVDF薄膜拉伸过程中α相受外力作用转变成β相。PVDF挤出片材在拉伸温度80℃、拉伸比5倍,拉伸速率50mm/min条件下进行拉伸时,薄膜中β相的相对含量可高达57%。     

电场极化与振荡剪切对聚偏氟乙烯β相形成的影响

通过电场极化、振荡剪切及以上两种外场同时作用于聚偏氟乙烯(PVDF)熔体,借助红外光谱仪对PVDF在外场作用下结晶形成β相的行为进行了研究。结果表明,电场极化作用能促进PVDF极性β相的形成,随着电场强度提高,β相含量逐渐增加。振荡剪切对β相的形成也有一定促进作用,β相含量随振荡频率的提高略有增加;但两种外场的同时作用,却并不表现出协同效果。     

聚偏氟乙烯压电薄膜的制备及结构

采用溶液浸渍提拉法制备了β型PVDF压电聚合物薄膜,采用X衍射、扫描电镜等手段测定了PVDF薄膜的物相结构,结晶形态及薄膜厚度等.结果表明,基板的诱导作用使PVDF在较低温度下结晶形成极性的正交β相晶,在较高温度下结晶形成非极性的单斜相α晶.在低温下得到的PVDF薄膜中β晶呈典型的球晶结构,晶粒粒径随着膜厚的增加而增大,α晶体颗粒的堆积疏松,薄膜致密性差;在较高温度下形成的α晶相,以二维生长为主,晶粒大小随着膜厚的增加基本上保持不变,晶颗粒间接触紧密,薄膜致密性好.     

动态硫化制备高密度聚乙烯/脱硫轮胎胶粉热塑性弹性体

采用固相力化学技术实现了废旧轮胎橡胶(GTR)的脱硫化及与高密度聚乙烯(HDPE)的复合,并采用动态硫化技术成功制备了HDPE/GTR热塑性弹性体(TPE)。结果表明,经力化学碾磨后,胶粉的凝胶含量显著降低。碾磨20次后,共混材料的拉伸强度由碾磨前的5MPa提高到8.6MPa;扯断伸长率由碾磨前的9.7%提高到63.3%。经动态硫化制备热塑性弹性体,材料的力学性能进一步提高,碾磨20次的复合粉体制备的TPE拉伸强度和扯断伸长率分别提高到10.6MPa和76.5%。所制备的TPE均保持了橡胶良好的回弹性,拉伸永久变形均保持在20%以内。扫描电子显微镜(SEM)研究表明经力化学处理制备的HDPE/GTR热塑性弹性体两相间具有良好的界面结合。     

KNN/PVDF纳米复合膜的制备及介电性能研究

采用聚合物前驱体法合成了K0.5Na0.5Nb O3(KNN)纳米粉体。X射线衍射(XRD)和扫描电子显微镜(SEM)分析表明,制备出的KNN粉体为单一的纯钙钛矿结构,并且其晶粒尺寸在15~25 nm之间。采用溶液混合法制备了KNN/聚偏氟乙烯(KNN/PVDF)纳米复合膜,研究了KNN纳米粉体的含量对复合膜微观形貌和介电性能的影响。结果表明,KNN纳米粉体均匀地分散在聚偏氟乙烯(PVDF)基体中,KNN/PVDF复合膜材料的介电常数和介电损耗均随着KNN含量的增加而增加。在1 k Hz下,当KNN质量分数为20%时,复合膜的介电性能较为优越,其介电常数为29.9,介电损耗为0.053。     

Piezoelectric formation mechanisms and phase transformation of poly(vinylidene fluoride)/graphite nanosheets nanocomposites

The β-phase of poly(vinylidene fluoride) (PVDF) is of great technical importance because of its high dielectric constant and piezoelectric effect. In this work, we exfoliated and dispersed natural graphite to prepare 2D-graphite nanosheets (GNS) and prepared PVDF/GNS nanocomposites with different GNS volumes from 1 to 7 ml as film via solution casting method. The concentration of the supernatant was about 0.3 mg/mL. The effect of GNS on the β-phase formation and mechanisms of piezoelectric formation in the PVDF/GNS nanocomposites were investigated. The results showed that with the varying amounts of GNS, the crystalline structure, the morphology, and the dielectric and piezoelectric properties of PVDF/GNS nanocomposites changed. GNS acts as an effective nucleation agent with the orientation almost parallel to the surface of the film meanwhile increasing the amount of beta phase in the PVDF matrix with increasing amount of GNS, also the relative dielectric constant and dielectric loss of the nanocomposites increased with increasing amount of GNS. The value d₃₃ also increased with increasing amount of GNS, and reached a maximum (6.7 pC/N) with 6 ml GNS. The mechanism of piezoelectric formation was proposed based on experiment results of PVDF/GNS nanocomposites.     

Influence of annealing on dielectric and polarization behavior of PVDF thick films

The polyvinylidene fluoride (PVDF) thick film has been fabricated by a solution casting method. The fabricated film is subjected to annealing at 50, 90, 100, 110 and 130?°C for 5 h. The effect of annealing on structural, crystalline, dielectric and polarization behavior is investigated. The β-phase PVDF is found to coexist with α-phase for annealing temperature upto 100?°C, after that β-phase is converted to α-phase. The film annealed at 100?°C, exhibits enhanced permittivity, reduced tangent loss and enhanced polarization. The dielectric permittivity and tangent loss of film annealed at 100?°C are ~11 and ~0.025 respectively for the frequency range of 10³–10⁵ Hz. The saturation polarization for this film is ~1.27 µC/cm². The enhanced dielectric permittivity and polarization for the film annealed at 100?°C might be attributed to increase in crystalline α and β-phase interface as well as crystalline amorphous interface. The thick film of PVDF with improved dielectric and polarization behavior could be useful for high power electronics application.     

石墨在固相剪切碾磨力场下的片层剥离及与PVC的纳米复合

采用固相剪切复合技术成功制备石墨-聚氯乙烯(PVC)复合粉体, 实现了石墨的片层剥离和在PVC基体中的纳米分散及对PVC的抗静电改性。通过XRD、 SEM、 TEM等表征了石墨-PVC/PVC复合材料的结构, 研究了其抗静电性能。结果表明, 石墨的片层厚度约20 nm, 径厚比超过10。固相剪切碾磨技术制备的石墨-PVC/PVC复合材料的导电性能有较大提高。在石墨质量分数为2%时, 表面电阻率为4.6×10⁷ Ω·cm, 已达到了抗静电材料的要求, 实现了低填充。在石墨质量分数为10%时, 表面电阻率达到最低的4.1×10⁴ Ω·cm。     

Large dielectric constant and high thermal conductivity in poly(vinylidene fluoride)/barium titanate/silicon carbide three-phase nanocomposites

Dielectric polymer composites with high dielectric constants and high thermal conductivity have many potential applications in modern electronic and electrical industry. In this study, three-phase composites comprising poly(vinylidene fluoride) (PVDF), barium titanate (BT) nanoparticles, and β-silicon carbide (β-SiC) whiskers were prepared. The superiority of this method is that, when compared with the two-phase PVDF/BT composites, three-phase composites not only show significantly increased dielectric constants but also have higher thermal conductivity. Our results show that the addition of 17.5 vol % β-SiC whiskers increases the dielectric constants of PVDF/BT nanocomposites from 39 to 325 at 1000 Hz, while the addition of 20.0 vol % β-SiC whiskers increases the thermal conductivity of PVDF/BT nanocomposites from 1.05 to 1.68 W m(-1) K(-1) at 25 °C. PVDF/β-SiC composites were also prepared for comparative research. It was found that PVDF/BT/β-SiC composites show much higher dielectric constants in comparison with the PVDF/β-SiC composites within 17.5 vol % β-SiC. The PVDF/β-SiC composites show dielectric constants comparable to those of the three-phase composites only when the β-SiC volume fraction is 20.0%, whereas the dielectric loss of the PVDF/β-SiC composites was much higher than that of the three-phase composites. The frequency dependence of the dielectric property for the composites was investigated by using broad-band (10(-2)-10(6) Hz) dielectric spectroscopy.     

Effect of filler size and concentration on the structure and properties of poly(vinylidene fluoride)/BaTiO<Subscript>3</Subscript> nanocomposites

The effect of filler size and content in the thermal, mechanical, and electrical response of poly(vinylidene fluoride) (PVDF)/BaTiO₃ nanocomposites has been investigated. Dielectric constant increases significantly with increasing filler content and decreasing filler size. Space charge effects at the interface between BaTiO₃ and PVDF strongly influence the dielectric response. The electroactive β-phase of PVDF is nucleated by the presence of the ceramic filler, the effect being strongly dependent on filler size and independent on filler content. This filler/matrix interaction is also responsible for the variations observed in the activation energy of the thermal degradation of the polymer. Smaller particles lead to larger relative contact areas and are responsible for the main variations observed in the thermal, mechanical, and electrical properties of the composites.     

废旧轮胎橡胶的常温应力诱导固相力化学脱硫化研究

利用固相力化学反应器实现对废旧轮胎橡胶的常温力化学脱硫化。实验结果,表明胶粉的交联密度和凝胶含量随碾磨次数增加显著降低,通过碾磨,再硫化橡胶的力学性能得到显著提高。碾磨40次后,拉伸强度由碾磨前2.3 M Pa提高到10.9 M Pa;断裂伸长率由碾磨前的69.6%提高到290.0%。再硫化胶的断面形貌分析表明,用脱硫胶制得的胶片具有良好的界面结合。     

The use of X-ray diffraction peak-broadening analysis to characterize ground Al2O3 powders

X-ray peak broadening has been used to study the milling behaviour of a number of commercial alumina powders. It is shown that the milling behaviour is dependent upon the original particle size, internal defects in particles and the milling liquid used. Peak-broadening studies allow the effects of milling upon reduction of crystallite size and increase in stored energy to be separated. The effect of these two parameters was separated using the Cauchy correction method. Measurement of the particle size of the unmilled alumina powders in the transmission electron microscope was used to determine that the Cauchy method gave the most correct estimation of crystallite size. Both alumina crystallite size and stored energy are expected to enhance sintering of the powder to a high density. Attempts are made to predict the sintering ability of the materials studied in terms of the above parameters.     

Dielectric and magnetic properties of ferrite/poly(vinylidene fluoride) nanocomposites

Particulate composite films of poly(vinylidene fluoride) and CoFe₂O₄ and NiFe₂O₄ were prepared by solvent casting and melt processing. The well-dispersed ferrite nanoparticles nucleate the piezoelectric β-phase of the polymer, but the different ferrites nucleate the whole polymer crystalline phase at different filler concentrations. The macroscopic magnetic and dielectric response of the composites demonstrates a strong dependence on the volume fraction of ferrite nanoparticles, with both magnetization and dielectric constant increasing for increasing filler content. The β-relaxation in the composite samples is similar to the one observed for β-PVDF obtained by stretching. A superparamagnetic behavior was observed for NiFe₂O₄/PVDF composites, whereas CoFe₂O₄/PVDF samples developed a hysteresis cycle with coercivity of 0.3 T.