Flame-retardant Wrapped Ramie Fibers towards Suppressing “Candlewick Effect” of Polypropylene/Ramie Fiber Composites

In this work, a flame-retardant polypropylene(PP)/ramie fiber(RF) composite was prepared. The ramie fibers were wrapped chemically by a phosphorus- and nitrogen-containing flame retardant(FR) produced via in situ condensation reaction so as to suppress their candlewick effect. Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM) demonstrated that the ramie fibers wrapped chemically by FR(FR-RF) were obtained successfully. Thermogravimatric test showed that the PP/FR-RF composite had more residue and better thermal stability at high temperatures than the PP/RF composite. Cone calorimeter(CC) results indicated that the peak of heat release rate(PHRR) and total heat release(THR) correspondingly decreased by 23.4% and 12.5% compared with the values of neat PP/RF. The PP/FR-RF composite created a continuous and compact char layer after the combustion. Combining FTIR analysis of char residue after CC test with heat conduction coefficient results, it could be concluded that the charring of FR on RF greatly weakened the candlewick effect of RF, and more char residue in the RF domain facilitated the formation of more continuous and compact char layer in the whole combustion zone, consequently protected PP composites during combustion, resulting in the better flame retardancy of PP/FR-RF composite than that of PP/RF composite.     

酶催化动力学光度法测定抗坏血酸

基于抗坏血酸对血红蛋白模拟酶催化体系的抑制作用,建立酶催化动力学光度法测定抗坏血酸的新方法。研究了体系的最佳条件及动力学行为,测定的线性范围为2.0×10-7—5.9×10-5mol/L,方法检出限为7.0×10-8mol/L。对6.0×10-6mol/L的抗坏血酸进行11次平行测定相对标准偏差为2.5%。此方法可用于药剂和蔬菜中抗坏血酸含量的测定。     

钛合金异质自冲铆接头力学性能及失效机理分析

对钛合金异质单搭及T型自冲铆接头进行拉伸-剪切实验和剥离实验,对比接头的静力学性能,用扫描电子显微镜对接头典型断口进行研究,分析其微观失效机理。结果表明:TA1-Q215接头的最大失效载荷大于相同搭接类型的TA1-AA5052接头;TA1-AA5052单搭接头因下板断裂失效,为韧性断裂特征;TA1-Q215单搭接头上板铆钉孔撕裂处为韧窝形貌,铆钉与下板分离过程中,下板发生塑性变形并与铆钉产生严重刮擦现象;TA1-AA5052T型接头因铆钉与下板分离失效,下板出现明显的撕裂棱;当TA1-Q215T型接头失效形式为铆钉与上板分离时,上板撕裂处为准解理断裂机制;当铆钉与下板分离时下板撕裂处为韧性断裂,铆钉从下板剥离过程中产生刮痕。     

Thermal Degradation,Flame Retardance and Mechanical Properties of Thermoplastic Polyurethane Composites Based on AluminumHypophosphite简

Aluminum hypophosphite （AP） was used to prepare flame-retarded thermoplastic polyurethane （FR-TPU） composites, and their flame retardancy, thermal degradation and mechanical properties were investigated by limiting oxygen index （LOI）, vertical burning test （UL-94）, thermogravimetric analysis （TGA）, cone calorimeter （CC） test, Fourier transform infrared （FTIR） spectroscopy, scanning electron microscopy （SEM） and tensile test. TPU containing 30 wt% of AP could reach a V-0 rating in the UL-94 test, and its LOI value was 30.2. TGA tests revealed that AP enhanced the formation of residual chars at high temperatures, and slightly affected the thermal stability of TPU at high temperatures. The combustion tests indicated that AP affected the burning behavior of TPU. The peak of heat release rate （PHRR）, total heat release （THR） and mass loss rate （MLR） greatly reduced due to the incorporation of AP. The tensile test results showed that both the tensile strength and the elongation at break slightly decreased with the addition of AP. The digital photos and SEM micrographs vitrified that AP facilitated the formation of more compact intumescent char layer. Based on these results mentioned above, the flame-retarding mechanism of AP was discussed. Both the self-charring during the decomposing process of AP and its facilitation to the charring of TPU led to the great improvement in the flame retardancy of TPU.     

基于异源自分类串联反应集成策略构筑不对称的1,4-二氢吡啶衍生物

假设不同结构的底物可以同时参与自分类的串联反应,而且各自生成的合适官能化的分子能够进一步发生汇聚反应,将更为有效地制备复杂的产物。在此基础上,我们建立了一个简单的反应模型来验证该策略的可行性。例如,在醋酸铵和间硝基苯甲醛的存在下,两种1,3-二羰基化合物可以经过两个并存的串联反应路径分别生成烯胺和烯酮中间体,二者随后汇聚选择性生成不对称的1,4-二氢吡啶.通过核磁直接检测反应液进一步证实了该反应的高度选择性,即不同底物发生串联反应的高度自分类且汇聚的特性.我们希望该结果能启发化学家通过更为有效的异源自分类串联反应集成策略实现由简单底物来高效制备复杂的分子.     

剪切应力场中聚丙烯熔体在近熔点处冷却结晶的晶体结构研究

通过自主设计的动态保压注塑成型装置研究剪切应力场下聚丙烯(PP)熔体在近熔点处冷却结晶的晶体结构.用扫描电子显微镜(SEM)、示差扫描量热法(DSC)和广角X射线衍射(WAXD)分析了PP试样在近熔点处冷却后从表层到剪切层的结晶结构的变化.SEM研究表明,与传统注塑成型样品(SL)和剪切力场中高熔体温度下冷却得到的试样(DH)相比,近熔点附近冷却得到的PP试样(DL)从表层到剪切层的结晶结构和形态有明显变化.DL从表层到剪切层均生成了尺寸较大的取向结晶结构,无明显的串晶产生.DSC研究表明,与SL和DH相比,DL剪切层无脊纤维晶熔融峰且晶片熔融温度较高,证明其样品内部晶片尺寸较大.WAXD进一步研究显示,DL内部主要晶面(110,040和130)的结晶尺寸与SL和DH相比并没有发生明显改变.     

An efficient halogen-free flame retardant for polyethylene: piperazinemodified ammonium polyphosphates with different structures

In this study, piperazine-modified ammonium polyphosphates(PA-APPs) with hierarchical structure were synthesized through ion exchange reaction. ~1H nuclear magnetic resonance(~1H-NMR), Fourier transform infrared spectra(FTIR), elemental analysis(EA), and inductively coupled plasma atomic emission spectroscopy(ICP-AES) confirmed that the PA-APPs with different structures were prepared successfully. Then these flame retardants were used alone as monocomponent intumescent flame retardant for low-density polyethylene(LDPE). Combustion tests demonstrated that the flameretardant efficiency of PA-APP containing about 7 wt% carbon(PA-APP_7) was significantly higher than that of the other PAAPPs with more or less carbon. The flame-retarded LDPE system with 30 wt% PA-APP_7 passed the UL-94 V-0 rating, and had the oxygen index(LOI) of 33.0%. Thermal analysis illustrated that the thermal decomposition behavior of PA-APP changed with incorporating different contents of PA. For all these PA-APPs, PA-APP_7 showed higher thermal stability than the other PA-APP flame retardants. All the experimental results proved that PA-APP_7 could reach the balance of an acid source, a blowing source, and a charring source as a mono-component intumescent flame retardant for LDPE. Further, it led to the formation of a compact intumescent char layer containing the structures of rich P―O―P, P―N―C, C=C, etc. during burning which in turn resulted in the excellent flame-retardant efficiency of PA-APP_7.     

水在甲缩醛与三聚甲醛合成聚甲氧基二甲醚中的作用研究

聚甲醛二甲醚（PODE）添加到柴油中,可以减少不完全燃烧造成的空气污染。在不同温度下,以HZSM-5为催化剂,三聚甲醛（TOX）和甲缩醛（DMM）为原料,加入不同含量的水以模拟甲醛原料水含量（0~10 wt%）对PODE合成的影响。结果表明：在相同的甲醛/甲缩醛摩尔比的条件下,随着TOX中水含量的增加,TOX和DMM的转化率变化不明显,而产物中PODE_3-8的含量则明显降低,从无水时的39.55%减少到3 wt%水时的32.09%,10 wt%水时的23.66%。同时,发现MeOH等的含量随着含水量的增加明显增加,由无水时的0.53%增加至3wt%水时的2.82%和10 wt%时的4.42%。进一步研究表明:反应体系中的水与MeOH的生成密切相关。通过物料衡算证实PODE合成过程中的水主要与DMM反应生成MeOH。      

Simultaneous improvement in the flame retardancy and water resistance of PP/APP through coating UV-curable pentaerythritol triacrylate onto APP

To improve the flame-retardant efficiency and water resistance of ammonium polyphosphate(APP), the UV-curable pentaerythritol triacrylate(PETA) was used to microencapsulate APP via the UV curing polymerization method. The prepared PETA-microencapsulated APP(PETA-APP) was characterized by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), and thermogravimetric(TG) analysis. PETA-APP was used as intumescent flame retardant(IFR) alone to flame retard polypropylene(PP). The water resistance of PP/PETA-APP composites was investigated, and the effect of PETA on the combustion behaviors of PP/APP composites was studied through limiting oxygen index(LOI), vertical burning test(UL-94) and cone calorimeter(CC) test, respectively. With 40 wt% of PETA-APP, the PP/PETA-APP system could achieve a LOI value of 30.0% and UL-94 V-0 rating after treatment in hot water for 168 h, while the LOI value of the system containing 40 wt% uncoated APP was only 19.2%, and it failed to pass the UL-94 rating. CC test results showed that the heat release rate(HRR), mass loss rate(MLR) and smoke production rate(SPR) of PP/PETAAPP system decreased significantly compared with PP/APP system, especially the peak of HRR was decreased by 51.4%. The mechanism for the improvement of flame reatardancy for PP/PETA-APP composites was discussed based on FTIR and X-ray photoelectron spectroscopy(XPS) tests. All these results illustrated that simultaneous improvement of flame retardancy and water resistance for PP/APP was achieved through coating UV-curable PETA onto APP.     

粘接剂对钛合金异质自冲铆接头力学性能的影响

为了研究粘接剂对自冲铆接头性能的影响,分别以TA1-5052和TA1-Q215的单搭自冲铆接头及粘接-自冲铆复合接头为研究对象,采用剖面直观检测法分析接头成形质量,基于静力学试验研究各组接头的静力学性能及失效形式。结果表明:与自冲铆接头相比,复合接头的钉脚张开度和残余底厚值减小;粘接剂对TA1-5052单搭自冲铆接头失效形式无影响,但改变了TA1-Q215单搭自冲铆接头的失效形式;复合接头的静力学性能比自冲铆接头更优;相对于自冲铆接头,TA1-5052复合接头静失效载荷增加了17.5%,能量吸收值增加了13.3%;TA1-Q215复合接头静失效载荷增加了6.8%,能量吸收值增加了25.8%。