Effect of tetraacid on the properties of ODPA/4,4′‒ODA polyimide foams

In this research, a new flexible polyimide (PI) foams was successfully prepared and characterized based on precursor powder foaming. This foams were derived from 3,3',4,4'‒oxydiphethalic anhydride (ODPA), 3,3',4,4'‒oxydiphethalic tetraacid (ODPA‒tetraacid), and 4,4'‒oxydianiline (4,4'‒ODA). With varying molar percentage of ODPA‒tetraacid in (ODPA + ODPA‒tetraacid), the changes of properties of PI precursor powders and PI foams were comparatively investigated. The foaming processes of PI foams were observed by a self‒made visualization device. The decomposition products of precursor powders were analyzed by thermogravimetry‒Fourier transform infrared spectroscopy (TG‒FTIR). The crystallinity of precursor powders was investigated by wide‒angle X‒ray diffraction (WXRD). The chemical structure of PI precursor powders and foams was analyzed by FTIR. The thermal properties of PI foams were tested by the methods of dynamic mechanical analysis (DMA), and TG/differential thermogravimetry (DTG) analysis. The cell structure of PI foams was observed by a scanning electron microscopy. The rebound resilience of PI foams was studied by a self‒made drop‒ball instrument. With the increasing of ODPA‒tetraacid, the inflation onset temperatures and inflation degrees of PI foams decreased from 210°C to 118°C and increased from 10 to 14.8 times, respectively. The crystallinity of PI precursor powders increased. The thermal stability of PI foams decreased. The cell structure of PI foams became more uniform and the rebound rates increased linearly. Besides, ODPA‒tetraacid did not yield any negative effect on the complete imidization of the PI precursor powder by the FTIR spectra. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

泡沫炭的最新研究进展

泡沫炭是一种新型的炭材料,具有密度小、强度高、导电、导热、热稳定、化学稳定等良好的物理和化学性能。制备泡沫炭的前驱体主要包括有机聚合物和中间相沥青,不同前驱体所制备的泡沫炭结构和性能也有一定差异。本文从泡沫炭的制备、改性、性能及应用等方面综述了近年来泡沫炭的最新研究进展,重点阐述了中间相沥青基泡沫炭的制备和性能,并指出了泡沫炭的未来研究方向。     

挤压脱水与普通浇筑成型纤维水泥板性能对比

研究了挤压脱水成型与普通浇筑成型方法对纤维增强水泥板收缩及抗弯性能的影响.结果表明:在相同水灰比下,挤压脱水成型的纤维增强水泥板比普通浇筑成型的纤维增强水泥板收缩小,且其收缩发展速率比后者快;2种成型方法对PP纤维增强水泥板的力学性能影响不大,但对PVA纤维增强水泥板力学性能有一定影响,其影响程度与水灰比有关;无论是抗弯承载力还是抗弯延性,PP纤维增强水泥板均不如PVA纤维增强水泥板;对于普通浇筑成型,随着水灰比的增加,纤维增强水泥板的极限抗弯承载力有所下降,而抗弯延性却有所改善.     

The feeding value of extruded corn grain in a corn silage-based ration for high-producing Holstein cows and heifers during mid lactation

The objective of this study was to investigate the feeding value of extruded corn in a corn silage-based ration for high-producing Holstein cows during mid lactation. Sixteen multiparous and 8 primiparous Holstein cows (106 ± 49.7 d in milk; 43.7 ± 5.27 kg of milk/d) were paired based on parity, days in milk, milk production, and body condition score and assigned to 1 of 2 dietary treatments in a randomized block design for 10 wk including a 2-wk adaptation period. Cows were fed a total mixed ration and milked 3 times per day. Diets contained 44% forage (3:1; corn silage:grass silage), 44.7% grain, and either extruded corn (EXC) or finely ground corn (FGC) at 11.3% of ration dry matter. No significant differences were detected in dry matter intake, milk protein yields, fat-corrected milk yields, or body condition score between cows fed FGC and cows fed EXC. Multiparous cows fed EXC produced more milk during wk 3 through 8 with a reduced milk fat content compared with multiparous cows fed FGC. Milk protein content was greater for primiparous cows fed EXC during wk 5 through 8 compared with primiparous cows fed the FGC ration. The major effect of feeding 2.7 kg/d of EXC compared with FGC was an increase in milk production and a reduction in milk fat content for multiparous cows, and an increase in milk protein content for primiparous cows.     

膨化颗粒饲料真空喷涂油、水的工艺参数研究

使用小型真空喷涂装置对直径4mm膨化颗粒饲料进行了真空喷涂油脂、水时工艺参数对颗粒硬度、喷涂均匀度的影响的研究，结果表明：在喷涂油脂时，真空度、泻压时间和油温对于颗粒硬度均有不同的影响；真空度、油温对喷涂均匀度有显著影响。在喷涂水溶液时，真空度、泻压时间对颗粒硬度均有较大的影响；真空度对喷涂均匀度有显著影响。     

粗酚部分替代苯酚制备酚醛泡沫保温材料

采用多聚甲醛、粗酚和苯酚为原料制备了酚醛泡沫保温材料,研究了聚合时间、聚合温度、醛酚[多聚甲醛与总酚(粗酚和苯酚的总称)]摩尔比、催化剂用量和粗酚替代量等合成条件对可发性酚醛树脂性能的影响。经优化的酚醛树脂合成条件:聚合时间为3.0 h,聚合温度为85℃,醛酚摩尔比为1.60,催化剂用量为0.04 mol(总酚1.00 mol),粗酚替代量为总酚质量的30%。酚醛泡沫(表观密度为45 kg/m3)的导热系数为0.028 W/(m.K),氧指数为36%,压缩强度为0.29 MPa。     

Synergistic effects of hydroxides and dimethyl methylphosphonate on rigid halogen‐free and flame‐retarding polyurethane foams

Rigid halogen‐free and flame‐retarding polyurethane foams are prepared with aluminum hydroxide, brucite, and DMMP. The effects of the hydroxides and DMMP on the foaming process and flame retarding properties of the foams are investigated by thermo gravimetric analysis, limiting oxygen index, and X‐ray powder diffraction. The thermal stability of the rigid polyurethane foams is close to that of the hydroxide fillers, with aluminum hydroxide providing better flammability performance than brucite. The hydroxide fillers and DMMP play a synergistic role in the rigid polyurethane foams and the limiting oxygen indices are up to 28.4% and 32.4%, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structures and properties of closed‐cell polyimide rigid foams

Closed‐cell polyimide rigid foams with different Calculated Molecular Weight (Calc'd M_n) and foam density (ρ) have been prepared by thermal foaming of nadimide‐endcapped imideoligomers (NAIO) powder. The NAIO powder was obtained by thermally treating of a PMR poly(amide ester) solution derived from the reaction of diethyl ester of 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (α‐BPDE) and p‐phenylenediamine (p‐PDA) using monoethyl ester of cis‐5‐norbornene‐ endo‐2,3‐dicarboxylic acid (NE) as reactive endcapping agent in ethyl alcohol. Effect of Calc'd M_n and foam density (ρ) on mechanical and thermal properties of the polyimide rigid foams have been systematically investigated. It was found that the thermal foaming properties of NAIO powders were affected by the Calc'd M_n. The appreciate Calc'd M_n could yield polyimide foams with both high closed‐cell content (C_c) (>80%) and outstanding mechanical properties. Moreover, the thermal properties were reduced by increasing of Calc'd M_n and the mechanical properties improved gradually by increasing foam densities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3282–3291, 2013     

Effects of foam composition on the microstructure and piezoelectric properties of macroporous PZT ceramics from ultrastable particle-stabilized foams

Porous lead zirconate titanate (PZT) ceramics could be produced by combining the particle-stabilized foams and the gelcasting technique. In this study, the foaming capacity of particle-stabilized wet foams was tailored by changing the concentration of valeric acid and pH values of suspension. Accordingly, porous PZT ceramics with different porosity, microstructure, dielectric and piezoelectric properties were prepared with the respective wet foam. Increase in the porosity led to a reduction in the relative permittivity (ε_r), a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃) and a rapid decline in the transverse piezoelectric strain coefficient (d₃₁), which endowed porous PZT ceramics with a high value of hydrostatic strain coefficient (d_h) and hydrostatic figure of merit (HFOM). As a result, the prepared samples possessed a maximal HFOM value of 19,520×10^?15 Pa^?1 with the porosity of 76.3%. The acoustic impedance (Z) of specimens had the lowest value of 1.35 Mrayl, which could match well with those of water or biological tissue; accordingly, the material would be beneficial in underwater sonar detectors or medical ultrasonic imaging.