基于时空分布模型的混凝土面板堆石坝挤压边墙变形监测资料分析

基于挤压边墙多测点变形监测资料,通过引入监测点的空间坐标标量,结合场理论建立了挤压边墙变形时空分布模型。结合建设中的涔天河水库扩建工程挤压边墙的实测变形资料,验证了本文建立的挤压边墙变形时空分布模型。结果表明,该混凝土面板堆石坝挤压边墙的监测区域上部仍处于发展状态,尚不适合面板混凝土的施工。     

Recovery of n-3 polyunsaturated fatty acids and conjugated linoleic acids in ripened cheese obtained from milk of cows fed different levels of extruded flaxseed

The aim of the study was to investigate whether the addition of extruded flaxseed (EF) in dairy cow diets had an effect on milk fat and individual fatty acids (FA) recovery in cheese after 90 d of ripening. Eighteen Holstein-Friesian cows, divided into 3 experimental groups (6 cows/group), were fed 3 isonitrogenous and isoenergetic diets with 0 (CTR), 500 (EF500), or 1,000 g/d (EF1000) of EF in 3 subsequent periods (2 wk/each), following a 3 × 3 Latin square design. Dry matter intake (DMI) and milk yield were recorded daily. Individual milk samples were collected on d 7 and 13 of each period to determine proximate and FA composition. Eighteen cheese-making sessions (2 for each group and period) were carried out, using a representative pooled milk sample obtained from the 6 cows of each group (10 L). At 90 d of ripening, cheeses were analyzed for proximate and FA composition. Cheese yield was computed as the ratio between the weights of ripened cheese and processed milk. Recoveries of fat, individual FA, and grouped FA were computed as the ratio between the corresponding weights in cheese and in milk. Inclusion of EF did not affect DMI, milk yield, or milk composition. Compared with CTR, the 2 diets containing EF increased the proportion of C18:3n-3 and total n-3 FA, in both milk and cheese. Cheese yield and cheese fat percentage did not differ among diets. Likewise, milk fat recovery in cheese was comparable in the 3 treatments and averaged 0.85. The recoveries of individual FA were, for the most part, not dissimilar from fat recovery, except for short-chain saturated FA (from 0.38 for C4:0 to 0.80 for C13:0), some long-chain saturated FA (0.56 and 0.62 for C20:0 and C21:0, respectively), and for C18:3n-6 (1.65). The recovery of saturated FA was lower than that of monounsaturated FA, whereas recovery of polyunsaturated FA was intermediate. Compared with medium- and long-chain FA, short-chain FA were recovered to a smaller extent in cheese. No differences in recovery were found between n-6 and n-3 FA. In conclusion, FA have different recoveries during cheese-making, with lower values for the short-chain compared with long-chain FA, and for saturated FA compared with unsaturated FA. The addition of EF in dairy cow diets did not influence cheese yield or fat recovery in cheese, irrespective of the inclusion level. The experiment confirmed that feeding cows with EF represents a successful strategy for improving the FA profile of dairy products, through an increase of n-3 FA.     

Effect of valeric acid on the agglomeration of zirconia particles and effects of the sintering temperature on the strut wall thickness of particle-stabilized foam

Highly porous zirconia ceramics were prepared utilizing a particle-stabilized direct foaming technique in which the hydrophilic characteristic of zirconia particles was altered by the in situ adsorption of valeric acid on its surface. These surface modified zirconia particles are irreversibility adsorbed at the air/water interface and create an armor coating around the bubbles to stabilize them. In this study, the foamability and stability of zirconia foam were investigated by varying the valeric acid concentration, and zirconia foam with a foam volume of approximately four times the colloidal system volume was successfully prepared. The sintered foam has cell size ranging from 50 to 150 μm and the pore structure was characterized by mercury porosimetry. The effects of the sintering temperature on the grain size, strut wall thickness, and tetragonal phase were studied and correlated with an increase in the mechanical strength to 3.5 MPa with porosity of more than 90%.     

一模多孔铝合金型材牵引技术的应用

采用Solidworks对一模多孔铝型材挤压技术进行了模拟,模拟结果表明:在一模多孔挤压过程中,不同孔的料受力不均匀,左上方受力最大,右下方受力最小;对恒定牵引力7 kN下一模多孔挤压过程进行模拟发现,在牵引力的作用下,各孔料受力变得均匀。基于模拟结果,提出了双头单轨牵引技术的工艺路线,并在14 MN挤压生产线上进行试验,在牵引机作用下,一模多孔铝型材平直,表面质量良好。     

聚丙烯珠粒发泡研究进展

聚丙烯(PP)珠粒发泡材料具有优异的耐热、隔音、抗冲击以及耐化学腐蚀等性能,近年来被广泛应用在包装、建筑、汽车等行业。PP在其熔点温度附近的熔体强度会急剧下降,低熔体强度导致其难以得到好的泡孔结构,所以PP珠粒发泡的技术难度大,目前只有少数国家掌握了PP珠粒发泡的技术,因此PP珠粒发泡的研究受到了国内外的广泛关注。文中从制备工艺、发泡装备、性能改进、表征方法等方面综述了近年来国内外PP珠粒发泡的研究动态,并对该领域今后的研究方向进行了展望。     

Reinforced and hardened three-phase-foams

Currently and in the past several lightweight materials were evolved focusing on different applications. Many developments are based on biomimetic approaches to reach material and cost savings with a simultaneous combination of thermal insulation and sustainability, for example. The desire of needed high porosity and lower density lead to less strength of the materials. Thus, applications are limited. One way to solve this problem is the creation of foams based on three phases. A new approach is the implementation of nanotubes and further chemical treatment of the inorganic foams to avoid further energy consuming thermal treatment for strengthening. Three-phase-foams consist of pozzolanic active nanomaterials as a third phase, which can be varied and surface treated. The resulting materials can be combined with other binders to further improve their properties or used as self-contained materials.Aided by chemical treatment a hardening of the foams has been achieved. Implementation of prefabricated and synthesized nanotubes as a nanoreinforcement were successfully done and properties of the foams investigated. Results based on studies of the microstructure and phase formation will be illustrated and discussed.     

Foam injection molding of poly(lactic acid) with environmentally friendly physical blowing agents

Biodegradable polymers present a very narrow processing window, with the suitable processing temperatures close to the degradation conditions. The aim of this work was to analyze the foamability of a biodegradable polymer, namely the poly(lactic acid), PLA. Foam injection molding was conducted by using a blowing agent under high pressure and temperature to produce parts having a cellular core and a compact solid skin (the so-called “structural foam”). The effect of a physical blowing agent (PBA) on density and morphology of foamed parts was characterized. A masterbatch of PLA and talc was prepared and adopted to obtain a compound containing 3% of talc. On adding this percentage of talc to PLA it was possible to obtain foamed parts with a much better morphology.     

Smoke and toxicity suppression by zinc salts in flame‐retardant polyurethane‐polyisocyanurate foams filled with phosphonate and chlorinated phosphate

Three types of zinc salts, ZnAl₂O₄, ZnFe₂O_4, and Zn₂SiO_4, were prepared by coprecipitation. Potential smoke and toxicity suppression by zinc salts in flame‐retardant polyurethane‐polyisocyanurate foams (FPUR‐PIR) with dimethylmethylphosphonate (DMMP) and tris (2‐chloropropyl) phosphate (TCPP) were investigated. The crystal structure and dispersity of zinc salts in FPUR‐PIR were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Smoke density, flame retardancy, and thermal degradation were studied using smoke density rating (SDR), limiting oxygen index (LOI), the cone calorimeter test, and thermogravimetry coupled with FTIR spectrophotometry (TGA‐FTIR). The results indicated that pure zinc salts were obtained and evenly dispersed on the cell wall of FPUR‐PIR. SDR and the specific extinction area (SEA) were significantly decreased, the time to second heat release rate peak (pk‐HRR) of FRUP‐PIR was delayed after incorporation of the zinc salts; zinc salts partially inhibited phosphorus oxide release into the gas phase, enhanced the condensed phase effect of phosphorus, reduced, and prolonged the release of isocyanate compound and hydrogen cyanide from FRUP‐PIR; due to an increase in the amount of char residues, which indicated the suppression of smoke and toxicity volatiles. ZnFe₂O₄ resulted in better char formation at the initial degradation stage of FPUR‐PIR, and ZnAl₂O₄ retained more phosphorus in the solid phase at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41846.     

Influence of the nanofiber dimensions on the properties of nanocellulose/poly(vinyl alcohol) aerogels

The investigation of aerogels made from cellulose nanofibers and poly(vinyl alcohol) (PVOH) as a polymeric binder is reported. Aerogels based on different nanocellulose types were studied to investigate the influence of the nanocellulose dimensions and their rigidity on the morphology and mechanical properties of the resulting aerogels. Thus, cellulose nanocrystals (CNCs) with low (10), medium (25), and high (80) aspect ratios, isolated from cotton, banana plants, and tunicates, respectively, microfibrillated cellulose (MFC) and microcrystalline cellulose (MCC) were dispersed in aqueous PVOH solutions and aerogels were prepared by freeze‐drying. In addition to the cellulose type, the PVOH‐ and the CNC‐concentration as well as the freeze‐drying conditions were varied, and the materials were optionally cross‐linked by an annealing step or the use of a chemical cross‐linker. The data reveal that at low PVOH content, rigid, high‐aspect ratio CNCs isolated from tunicates afford aerogels that show the least amount of shrinking upon freeze‐drying and display the best mechanical properties. However, with increasing concentration of PVOH or upon introduction of a chemical cross‐linker the differences between materials made from different nanocellulose types decrease. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41740.