Fabrication Mechanical Properties of Unidirectional Jute/PP Composites Using Jute Yarns by Film Stacking Method

This paper mainly focuses on the fabrication process of long fibre reinforced unidirectional thermoplastic composites made using both natural (untreated) treated jute yarns. Jute yarns were wound in layers onto a metallic frame. Polypropylene films were inserted between these layers and compression moulded to fabricate unidirectional jute/PP composite specimens. Static mechanical properties were evaluated from tensile three point bending tests. Pre- post-failure examination were carried out on the test specimens using optical scanning electron microscopy to analyse the test results and investigate the correlations between their impregnation state, processing conditions, mechanical performances and fracture morphologies. For the unidirectional jute/PP film-stacked composites, the results indicated that the processing condition at the moulding temperature of 160°C and moulding pressure of 2.0 MPa for 15 min was ideally suited to obtain optimized properties. Improved wettability of resin melts due to complete matrix fusion at this processing condition facilitated thorough impregnation with minimum microstructural imperfections (microvoids) being generated. Jute/PP composites that contained treated jute yarns have shown superiority in tensile bending properties. Jute yarns polished or coated with PVA/PP (polyvinyl alcohol/polypropylene) must have contributed positively to fibre/matrix interfacial interactions leading to matrix to fibre effective stress transfer, thereby improving their reinforcing effects. Tensile strength and modulus of PP resin increased by approximately 285% and 388%, respectively, due to 50 wt% reinforcement by natural jute yarns. Further improvements in strength and modulus were achieved by approximately 14% and 10%, respectively, when treated yarns were used . The maximum bending stress modulus of jute/PP composites containing untreated yarns were approximately 190% and 460% higher than those of the virgin PP materials, and bending properties were improved by further 11% and 23%, respectively, due to coating treatments on the yarn surface.     

微/纳米颗粒表面能测定方法适用性研究

采用静态液滴法、柱毛细法、板毛细法3种方法,分别测定了水、正己烷、甲酰胺、二碘甲烷4种液体与TiO_2(40 nm)、TiO_2(100 nm)、Al_2O_3(200 nm)、高岭土(200~400nm)、Fe_2O_3(400~600 nm)、SiO_2(20μm)6种粒径微/纳米颗粒之间的接触角,确定了适用于不同颗粒粒径的接触角测定方法.在此基础之上,利用Young-Dupré方程计算了各微/纳米颗粒的表面能及各分项.结果表明:粒径较小的颗粒(如200 nm)接触角的测定适合使用静态液滴法,而粒径较大的颗粒(如600 nm)接触角的测定适合使用柱毛细法.粒径大小适中时(如200~600 nm),静态液滴法和柱毛细法都适用,测定结果差别普遍较小(≤11°),但二碘甲烷与Fe_2O_3(400~600 nm)之间的接触角利用不同方法测定结果相差可达14°.静态液滴法操作方便,但由于粗糙度的影响需要对接触角测定值进行修正.板毛细法测定接触角时,液体容易挥发,不易得到准确测量结果,不推荐使用.对全部6种测定的微/纳米颗粒,表面能的计算结果相差不大.表面能的3个分项中,范德华分量(γLW)与路易斯碱分量(γ-)的贡献最大,路易斯酸分量(γ+)的贡献很小,主要是因为在微/纳米颗粒-液体界面中,电子受体的反应活性较低.     

频域子结构方法在力学环境预示中的应用研究

目的利用频域子结构方法(FBSM,FRF Based Sub-structuring Method)对结构的力学环境进行准确高效地预示。方法分别对处理子结构间为刚性连接和弹性连接两种问题的FBSM进行理论推导。为了验证FBSM的正确性,设计连接为刚性连接和弹性连接两种算例结构,并将FBSM对算例结构频响函数的计算结果与有限元方法(FEM,Finite Element Method)的对应计算结果进行对比。其中,弹性连接利用空间梁单元进行等效,并将该等效方法与利用六自由度标量弹簧的等效方法进行对比。结果对于刚性连接和弹性连接两种情况,FBSM对频响函数的计算结果均与FEM的对应计算结果吻合程度良好。此外,空间梁单元的结点刚度矩阵为非对角阵,与六自由度标量弹簧相比,可更为准确地等效工程实际中的弹性连接。结论FBSM可对结构的力学环境进行准确高效的预示,且在处理具有弹性连接结构的力学环境预示问题时,可采用空间梁单元等效弹性连接。     

等离子球磨机的研制及其振动平台试验

目的实现球磨室在常压下的大面积介质阻挡放电等离子体,开发出商用等离子球磨机。方法通过在不同弹簧和平台质量条件下,利用振动传感器测试平台的振幅(峰峰值)和加速度(有效值)数值,对比确定最优配置和机械振动参数。结果当振动平台振幅接近球磨室内径时,获得高振幅和高加速度的磨球,显著缩短了气体放电间距,实现了球磨室在常压下的大面积介质阻挡放电等离子体。所设计的单筒等离子振动球磨机,其振动平台可选用φ7 mm、φ8 mm两组弹簧,根据平台质量的不同,选择不同类型的激振块组合,可以在30 Hz转速以上实现平台振幅峰峰值达到或者接近球磨罐内径值,同时拥有10g以上的加速度有效值。结论本试验综合机械振动学、高压绝缘放电和材料加工技术,所研制的等离子体球磨机实现了机械能和等离子体能在球磨过程中的协同作用,显著提高了粉末活性,降低了化合物合成反应激活能,从而显著提高了所制备材料的性能。     

Toxicity of the venom in three neotropical Crematogaster ants (Formicidae: Myrmicinae)

Bioassays were performed to investigate and compare the toxic properties of the contact venoms of three Neotropical Crematogaster species (C. sp. prox. abstinens, C. distans and C. brevispinosa rochai), whose main venom compounds are chemically different (long chain derivatives linked to an aldehyde or a primary acetate, and furanocembrenoid diterpenes, respectively). Different quantities of venom were topically applied on the bodies of three target insect species (workers of the termite Nasutitermes ephratae, workers of the ant Solenopsis sp., “media” and “major” workers of the ant Cephalotes pusillus). The toxicity of the venom greatly varied according to the Crematogaster species, the venom of C. b. rochai showing the highest toxic activity towards all target species. The sensitivity of the target species also greatly varied, the workers of N. ephratae showing a great sensitivity to the venoms, while the heavily armoured workers of the ant C. pusillus, particularly “major” ones, were resistant. Cuticle thickness was found to be a key factor in the resistance to the toxic effects of Crematogaster venom. Sensitivity of the target workers was also directly related to the amount of venom applied to their cuticle. Workers of C. distans were resistant to topical application of their own venom, while C. sp. prox. abstinens and C. b. rochai were not. In all cases, the venoms were slow acting, as several hours to one or even several days were needed to obtain a significant mortality. The main biological activities of the Crematogaster venom could be related to more immediate repellent properties, as recently shown with the European species C. scutellaris.     

电选法回收利用废印刷线路板

废印刷线路板含有多种有价值的物质,随意丢弃或处理处置方法不当既污染环境,又造成资源流失。采用剪切式破碎和电力分选技术对废印刷线路板的机械分离进行了研究。结果表明,电选法可以实现废印刷线路板中金属和玻璃纤维、树脂的分离;在实验的粒径范围内(-14+20目到-120+200目分为5个粒径级别),金属主要集中在-20+120目粒级范围内,且该粒级范围分选效果最好。     

含铌微合金钢焊接性能研究

采用金相及透射电镜等方法研究了含铌微合金钢 14MnNbq焊接时焊缝区的组织特征 ,测试了其力学性能 ,结果表明钢中由于Nb的存在 ,使焊接区及热影响区组织发生变化 ,粗晶区得到细化 ,同时降低了焊缝脆化的倾向 ,使钢具有良好的焊接性能与力学性能。     

港口污水膜生物反应器回用处理技术研究

系统地论述了膜生物反应器的反应特征、去除机理，及其在港口污水中水回用处理应用的可行性。结果表明，膜生物接触氧化法用于港口污水处理，具有出水水质稳定、占地面积少、去除效率高等特点。经预处理后的港口污水再行由膜生物接触氧化反应器处理后可直接用作回用水。     

含制药残液废水的处理工艺研究

探讨了含制药残液废水的预曝-生物接触氧化-混凝沉降处理工艺。研究结果表明,经石灰乳调pH8.0曝气48h的废水,COD_(Cr)去除率可达47.5％;采用出水回流,进水COD_(Cr)1500～4000mg/L时,负荷为1.00～2.67kg/m~3·d,COD_(Cr)去除率超过86％;生化出水经投加PAC52.8mg/L,COD_(Cr)去除率为64.8％,达到国家工业废水排放标准。     

水源水生物处理工艺中亚硝酸盐氮的去除

通过中试规模试验系统 ,分析了不同运行条件下微污染水源水生物接触氧化处理工艺中亚硝酸盐氮的去除状况 ,探讨了亚硝酸盐氮积累量与氨氮去除率之间的关系。指出处理系统中硝酸盐细菌对亚硝酸盐细菌生化过程的依赖作用是亚硝酸盐氮积累的内因 ,而工艺参数等运行条件的变化是亚硝酸盐氮积累的外因 ,提高氨氮去除率是去除亚硝酸盐氮的关键。