Variation of MUF and PMUF resins mass fractions during preparation

The variation of molecular mass distribution with the progress of the reaction was studied for the following: (i) sequential‐type melamine–urea–formaldehyde (MUF) resin formulations in which the sequence of addition of chemicals follows well‐defined species reactivity principles; (ii) a nonsequential MUF formulation in which simultaneous melamine and urea competition for formaldehyde yields a MF resin cocondensed with small amounts of urea. This resin became soaked with reacted and unreacted monomeric urea species. (iii) A PMUF resin, namely a MUF resin with a small proportion of phenol (7.8% by weight on melamine and urea) cocondensed with the main MUF fraction. All the formulations used were industrial resins formulations in current use. Development and variation of molecular mass fractions, from which performance and other useful resin parameters depend, have been found to depend on the type of resin formulation used for these type of aminoplastic resins. The two very different MUF resin formulations yielded different variations in molecular mass fractions during the progress of the reaction and during the so‐called ambient temperature “maturing” of the resin. The PMUF resin also showed both similar and different fractions present during manufacturing and during short term ageing at ambient temperature. While similarities in recurrent fractions and in trends are common to all the three different formulations, differences between them are also clearly observed. A major proportion of the reaction of some of the aminoplastic resins examined also occurs on ageing (i.e.“maturing” of the resin at ambient temperature), this appearing to be an essential phase of the resin preparation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4842–4855, 2006     

Functionality distribution and crosslink density of hydroxyl-terminated polybutadiene

A novel approach is proposed for estimating the average molecular weight between crosslinks (M?_c) from the functionality distribution of hydroxyl-terminated polybutadiene ( HTPB ). The functionality distribution of four free-radically polymerised HTPB prepolymers of varying hydroxyl content and molecular weight was determined by a combination of preparative and analytical gel permeation chromatography. The gumstock properties of the samples cured with stoichiometric amounts of toluene diisocyanate were not correlatable with the relative amounts of difunctional chain extender and multifunctional crosslinker present, unlike the case of HTPB with similar hydroxyl content and molecular weight. However, the mechanical properties and sol content could be correlated with the average molecular weight between crosslink sites, M?_c, of the cured polymer. The M?_c values derived by our method compare well with those of classical methods, and the observed differences are attributed to segmental entanglement. These M?_c values give consistently good correlation with all the gumstock properties, confirming the validity of our approach and the soundness of the techniques developed for the determination of the functionality distribution of HTPB .     

基于广义预测的双电机同步控制

为减小多电机运动过程中的同步误差,提出了基于广义预测控制的两轴同步控制算法,其基本思想是在二次性能指标中加入同步误差的影响,使得该性能指标对单轴的跟踪误差、控制增量以及两轴之间的同步误差同时进行有限时段内的在线滚动优化,所得到的控制规律包含了两轴之间的交叉耦合作用,克服了单个电机受到扰动时两轴不能精确同步的问题,且该算法对系统的建模精度要求较低,在线滚动优化对负载扰动、随机噪声有很好的抑制作用。Matlab仿真实验结果表明,该控制算法能获得良好的单轴跟踪精度、两轴同步精度以及抗干扰能力。     

一种改进的广义预测控制算法

为了解决广义预测控制(GPC)算法本身计算量大以及无法兼顾快速性和超调的问题,提出了一种改进的广义预测控制算法。首先介绍了广义预测控制的基本算法和一种新型算法,包括算法的基本理论和优缺点,然后经过一定的数学分析,提出了一种改进算法,最后对3种算法进行了Matlab仿真,以比较静态误差。实验结果表明,该改进算法不仅能大大减少计算量,而且能很好地抑制超调,同时兼顾了快速性。     

凝胶色谱净化-毛细管气相色谱法测定渔业水体中乐果

建立凝胶色谱净化-毛细管气相色谱法测定养殖水体中乐果的分析方法。三氯甲烷萃取水样,经凝胶渗透色谱(GPC)净化除去脂类、色素等,采用脉冲不分流进样模式气相色谱法分析,外标法定量。方法检测限为0.022μg/L;加标水平为1.00μg/L时,实际样品回收率为82.5%～97.1%。该方法自动化程度高、净化效果好、重现性好、准确灵敏。实际样品检测结果表明,此方法满足复杂水体中乐果残留检测要求。     

Characterization of enzyme‐deproteinized skim rubber

Skim natural rubber latex is a protein‐rich byproduct obtained during the centrifugal concentration of natural rubber latex. Skim latex has a very low dry rubber content (4–8%), and the rubber particles are smaller in size. It has a higher proportion of nonrubber solids, which are mostly proteinaceous in nature. It is difficult to coagulate, and it takes more processing time. The proteins in skim latex can be decomposed by proteolytic enzymes. This article discusses the use of stabilized liquid papain from the papaya plant (Carica papaya) for deproteinization followed by creaming for quick and easy coagulation of skim latex. The technological properties and aging characteristics of the deproteinized skim rubber are compared with those of conventionally prepared skim rubber and block rubber. The deproteinized skim rubber showed enhanced quality parameters. Particle size analysis revealed that deproteinization and creaming of the skim latex did not markedly change the particle size. Gel permeation chromatography showed a reduction in the quantity of fatty acids after deproteinization and creaming, which was reflected in the improvement of the aging characteristics in comparison with the control sample. Vulcanizates prepared with the deproteinized skim rubber had higher resilience, lower heat buildup, lower compression set, and good tensile strength and elongation at break in comparison with conventionally prepared skim rubber, and the properties were almost comparable to those of block rubber. The improvement in the mechanical properties and aging characteristics could be attributed to the reduction of the protein content, the partial removal of unsaturated fatty acids, and the removal of metal ions that were pro‐oxidants during the deproteinization and creaming process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Simultaneous continuous,nonchromatographic monitoring and discrete chromatographic monitoring of polymerization reactions

Automatic continuous nonchromatographic monitoring and discrete chromatographic monitoring were coupled together for the first time and used to monitor free radical and controlled‐radical polymerization reactions. This was achieved by adding a multidetector Size Exclusion Chromatography (SEC) system (alternatively termed Gel Permeation Chromatography, GPC) to the ACOMP platform (Automatic Continuous Online Monitoring of Polymerization reactions). The fact that the reactor solution is already preconditioned in the ACOMP front‐end to the concentration levels used in SEC makes direct coupling possible. Kinetics from two different types of reactions, Reversible Addition Fragmentation Transfer (RAFT) and free radical polymerization of butyl acrylate were studied, including the production of a bimodal population. Complementary and contrasting features from the continuous and SEC approaches are highlighted. The main advantage of the SEC detection is to follow the evolution of full molecular weight distributions (MWD), especially in ‘living’ type reactions, where polydispersity decreases with monomer conversion, whereas the continuous detection provides a much more detailed characterization of the reaction. Interestingly, in the case where a bimodal molecular weight distribution was produced, the continuous method automatically detected the onset of the second mode in a model independent fashion, whereas SEC could only discern the bimodality by applying preconceived models. The SEC approach will have valuable niche applications, however, such as when reactions are relatively slow, monitoring narrow polydispersity is of primary importance, and also in copolymerization and terpolymerization reactions where complex mixtures of reagents (e.g., RAFT agents, copper ions, etc.) make unfractionated spectroscopic resolution of comonomers difficult. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Methyl acrylate/1‐octene copolymers: Lewis acid‐mediated polymerization

Copolymerization of methyl acrylate (MA) with 1‐octene (1‐Oct) was conducted in the presence of free radical initiator, 2,2′‐azobis(2‐methylpropionitrile) (AIBN) using heterogeneous Lewis acid, acidic alumina. The polymers obtained were transparent and highly viscous liquids. The copolymer composition calculated from ¹H NMR showed alkene incorporation in the range of 10–61%. The monomodal nature of chromatographic curves corresponding to the molecular weight distribution in gel permeation chromatography (GPC) further confirmed that the polymers obtained are true copolymers. The number–average molecular weights (M_n) of the copolymers were in the range of 1.1 × 10⁴–1.6 × 10⁴ with polydispersity index of 1.75–2.29. The effects of varying the acidic alumina amount, time of polymerization, and monomer infeed on the incorporation of 1‐Oct in the polymer chain were studied. Increased 1‐Oct infeed led to its higher inclusion in the copolymer chain as elucidated by NMR. DEPT‐135 NMR spectral analysis was used to explicate the nature of arrangement of monomer sequences in the copolymer chain. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

循环模式DSG槽式太阳能集热器出口蒸汽温度控制策略研究

循环模式直接蒸汽发电(direct steam generation,DSG)强度变化的影响很大,并具有大滞后、大惯性、参数时变等特点。针对该控制对象,提出采用多模型切换受限增量广义预测控制策略,建立典型工况下的子模型并设计相应的控制器。按照跟踪实际工况的运行结果,根据模糊推理的隶属度概念评判子模型的匹配程度,选择适配的子模型和控制器整定参数,并采用输入增量加权控制律和等待周期法实现平滑切换和无扰切换。仿真分析表明,提出的控制策略与常规PI控制方法相比,具有响应速度快、无稳态偏差、系统输出波动小、降低了模型失配影响等优点。仿真结果验证了该控制模型和策略的可行性和有效性。