Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

A fluorescence spectroscopic study of a coagulating protein extracted from Moringa oleifera seeds

The fluorescence studies of coagulating protein extracted from Moringa oleifera seeds have been studied using steady-state intrinsic fluorescence. The fluorescence spectra are dominated by tryptophan emission and the emission peak maximum (lambda(max)=343+ or -2nm) indicated that the tryptophan residue is not located in the hydrophobic core of the protein. Changes in solution pH affected the protein conformation as indicated by changes in the tryptophan fluorescence above pH 9 whereas the ionic strength had minimal effect. The exposure and environments of the tryptophan residue were determined using collisional quenchers.     

Shear Bond Strength and Film Thickness of a Naturally Antimicrobial Modified Dental Luting Cement

Although several natural plants and mixtures have been known and used over the centuries for their antibacterial activity, few have been thoroughly explored in the field of dentistry. Thus, the aim of this study was to enhance the antimicrobial activity of a conventional glass ionomer cement (GIC) with natural plant extracts. The effect of this alteration on the bond strength and film thickness of glass ionomer cement was evaluated and related to an 0.5% chlorohexidine modified GIC. Olive leaves (Olea europaea), Fig tree (Ficus carica), and the leaves and roots of Miswak (Salvadora persica) were used to prepare an alcoholic extract mixture. The prepared extract mixture after the evaporation of the solvent was used to modify a freeze-dried glass ionomer cement at three different extracts: water mass ratios 1:2, 1:1, and 2:1. An 0.5% chlorhexidine diacetate powder was added to a conventional GIC for the preparation of a positive control group (CHX-GIC) for comparison. The bond strength to dentine was assessed using a material-testing machine at a cross head speed of 0.5 mm/min. Failure mode was analyzed using a stereomicroscope at 12× magnification. The cement film thickness was evaluated in accordance with ISO standard 9917-1. The minimum number of samples in each group was n = 10. Statistical analysis was performed using a Kruskal–Wallis test followed by Dunn’s post hoc test for pairwise comparison. There was a statistically insignificant difference between the median shear bond strength (p = 0.046) of the control group (M = 3.4 MPa), and each of the CHX-GIC (M = 1.7 MPa), and the three plant modified groups of 1:2, 1:1, 2:1 (M = 5.1, 3.2, and 4.3 MPa, respectively). The CHX-GIC group showed statistically significant lower median values compared to the three plant-modified groups. Mixed and cohesive failure modes were predominant among all the tested groups. All the tested groups (p < 0.001) met the ISO standard of having less than 25 µm film thickness, with the 2:1 group (M = 24 µm) being statistically the highest among all the other groups. The plant extracts did not alter either the shear bond strength or the film thickness of the GIC and thus might represent a promising additive to GICs.     

超高效液相色谱-串联质谱法同时测定食品接触材料及制品中9种抗氧化剂迁移量

为了评估食品接触材料及制品中抗氧化剂的迁移风险,采用超高效液相色谱-串联质谱法(UPLC-MS/MS)建立了同时测定食品接触材料及制品中9种抗氧化剂迁移量的方法。采用C18色谱柱对迁移实验后的食品模拟物中9种抗氧化剂进行分离,1 mmol/L氟化铵和甲醇为流动相洗脱,采用电喷雾离子源(ESI),多反应监测(MRM)正负离子模式进行扫描。结果表明,9种抗氧化剂的色谱分离效果良好,并在0.3~6 mg/L质量浓度范围内与其峰面积均呈良好的线性关系,检出限为0.1 mg/L。加标回收率为93.9%~106%,相对标准偏差(RSD)为0.80%~9.3%。该方法快速高效、线性范围好,适用于塑料食品接触材料及制品中9种抗氧化剂迁移量的检测。     

基于肟-氨基甲酸酯的超强自修复水性聚氨酯胶粘剂的制备及性能分析

基于肟-氨基甲酸酯热可逆成键原理, 利用可工业批量获得的二甲基乙二肟为构建单元, 设计合成了一类具有高强动态网络结构的水性乳液, 制备出综合性能与重复利用兼顾的聚氨酯胶粘剂; 通过变温红外光谱结合差式扫描量热仪分析了肟-氨基甲酸酯升温过程的可逆成键特性, 并利用动态力学谱仪对变温过程的网络松弛行为进行了研究. 结果表明, 合理的硬段含量与结构设计赋予了胶粘剂极高的粘结强度(25 MPa, 一般商业通用热熔胶的粘结强度< 6 MPa)、 优异的乳液稳定性(粒径<100 nm)以及接近97%的修复效率(160 ℃, 10 min下的剪切搭接实验). 该类乳液具有超强、 稳定及工艺可放大等特性, 为水性自修复胶粘剂的商业化开发提供了新途径和新思路.     

Sonochemical degradation of surfactants with different charge types: Effect of the critical micelle concentration in the interfacial region of the cavity

Ionic surfactants tend to accumulate in the interfacial region of ultrasonic cavitation bubbles (cavities) because of their surface active properties and because they are difficult to evaporate in cavitation bubbles owing to their extremely low volatilities. Hence, sonolysis of ionic surfactants is expected to occur in the interfacial region of the cavity. In this study, we performed sonochemical degradation of surfactants with different charge types: anionic, cationic, zwitterionic, and nonionic. We then estimated the degradation rates of the surfactants to clarify the surfactant behavior in the interfacial region of cavitation bubbles. For all of the surfactants investigated, the degradation rate increased with increasing initial bulk concentration and reached a maximum value. The initial bulk concentration to obtain the maximum degradation rate had a positive correlation with the critical micelle concentration (cmc). The initial bulk concentrations of the anionic surfactants were lower than their cmcs, while those of the cationic surfactants were higher than their cmcs. These results can be explained by the negatively charged cavity surface and the effect of the coexisting counterions of the surfactants.     

胶态磁组装光子晶体及其离子强度响应

采用细乳液聚合方法合成了聚合物包覆的磁性复合纳米粒子(MCNPs),通过磁场诱导组装制备得到胶态磁组装光子晶体(CMA-PCs).透射电子显微镜(TEM)和扫描电子显微镜(SEM)表征结果表明,MCNPs具有规整的球形形貌和明显的核壳结构,并且单分散性较好,平均粒径为112 nm,聚合物壳层厚约10 nm.MCNPs在外界磁场的作用下可以快速(1 s)组装形成光子晶体结构.当离子强度在0.03~0.75 mmol/L范围内变化时,CMA-PCs的衍射色呈现从橙红色到紫色的变化,反射波长从607 nm蓝移至434 nm,并且离子强度的响应在10 s内即可达到平衡,表明制得的CMA-PCs可以作为化学传感器应用于离子强度的半定量检测,并且具有简便、快速及裸眼可视化检测的优点.     

Compression after impact of flax/PLA biodegradable composites

A study of the impact behaviour and the post-impact residual strength of fully biodegradable composites is presented in this work. To this end, low-velocity impact tests and compressive residual strength tests were carried out on flax/PLA laminates. The results were compared with carbon/epoxy laminates, showing some important advantages in terms of absorbed energy and normalized residual strength. The reason was attributed to different energy absorption mechanisms; the main failure mode in flax/PLA laminates is fibre failure while residual strength of carbon/epoxy laminates is dominated by delaminations.     

Dielectric phenomena and electrical energy storage of poly(vinylidene fluoride) based high-k polymers

Since the discovery of relaxor ferroelectric behavior was firstly reported in irradiated poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) copolymer, many strategies have been developed to enhance the electrical energy storage capability, including copolymerization, grafting, blending and fabricating of multilayer. This review article mainly summarizes the recent progresses on these strategies and aims to motivate the development of novel PVDF-based polymers for electrical energy storage and dielectric applications.