Preparation of thermoplastic elastomer from natural rubber grafted with polystyrene

Thermoplastic elastomer was prepared from deproteinized natural rubber (DPNR) by graft-copolymerization of styrene, which was performed onto rubber particles of about 1 μm in diameter in latex stage with tert-butyl hydroperoxide/tetraethylenepentamine as an initiator. Suitable initiator concentrations were determined to be 3.3 × 10⁻² and 20 × 10⁻² mol/kg-rubber for the graft-coplymerization of styrene of 1.5 and 5.5 mol/kg-rubber, respectively, in which conversion and grafting efficiency of styrene were more than 90 mol% and 80 mol%, respectively. The resulting polystyrene, grafted onto the rubber particles, was characterized by size exclusion chromatography after ozonolysis. Morphology of the DPNR grafted with polystyrene (DPNR-graft-PS) was observed by transmission electron microscopy (TEM). Change in morphology after processing the DPNR-graft-PS at 150 °C was associated with change in mechanical properties, i.e. stress at strain of 1 and stress at break. The outstanding mechanical properties, maintained even after processing, were assigned to the thermoplasticity of the DPNR-graft-PS, based on the high conversion and high grafting efficiency.     

Reactive compatibilization of PA12/plasticized starch blends: Towards improved mechanical properties

Glycerol-plasticized starch (TPS)/polyamide 12 (PA12) blends were processed by melt mixing using two types of interfacial agent, i.e. diglycidyl ether of bisphenol A and a poly(ethylene-co-butyl acrylate-co-maleic anhydride) copolymer. Morphologies of the blends were tailored from the nature and amount of the interfacial agents. The average size of the dispersed phase was shown to decrease with the incorporation of the reactive agents and was proved to respect models, usually employed for conventional blends, for size predictions of the dispersed phase. By means of rheological experiments, it has been investigated whether the size reduction of the dispersed phase was coming from the compatibilization of the blend or from the viscosity changes due to chain extension in the matrix. The influence of the coupling agents on the viscoelastic behavior of the blend was characterized. Both interfacial agents led to increase the absolute complex viscosity but in the case of diepoxy reactive agent, the Newtonian flow behavior of complex viscosity totally disappeared in the low-frequency region. Mechanical properties of the TPS/PA12 blends were characterized and were proved to be strongly impacted by the use of interfacial agents. Elongation at break was enhanced as a consequence of a better adhesion between the matrix and the dispersed phase, whereas a decrease of the Young’s modulus was observed with increasing DGEBA content. Polyamide 12 crystallization in TPS/PA12 blends was found to be strongly dependent on DGEBA content while the introduction of maleic anhydride-grafted copolymer had no influence.     

Influence of thermal aging on tensile and creep behavior of thermoplastic polyurethane

Changes in mechanical and physical properties of polyurethane thermoplastic during aging at 70 °C and 90 °C were investigated. The loss weight response was analyzed by gravimetric measurements under these temperatures. Changes in appearance and morphology of TPU after thermal aging were revealed by optical microscopy. The prolongation of the thermal exposure time, up to 270 days, leads to a progressive increase in tensile strength. In fact, elastic modulus and stress at 200% of strain were increased with thermal exposure time. These results can be explained by the increase of thermal stability due to the increase of material rigidity and the decrease in chain mobility. The evolution of the mechanical properties from tensile tests seems to be well correlated to the creep behavior. Finally, Scanning Electron Microscopy (SEM) revealed the modification of TPU morphology fracture surface after thermal aging.     

基于光谱学分析的聚氨酯弹性体/聚磷酸铵/氢氧化铝复合材料阻燃机理研究

采用熔融共混技术,将聚磷酸铵(APP)和氢氧化铝(ATH)引入到聚氨酯弹性体(TPU)中,制备了一系列热塑性聚氨酯/聚磷酸铵/氢氧化铝(TPU/APP/ATH)复合材料。采用傅里叶红外光谱(FTIR)、X-射线光电子能谱(XPS)、扫描电镜(SEM)、激光拉曼光谱研究了TPU和阻燃TPU(FR-TPU)复合材料燃烧后炭渣的微观形貌、表面结构、元素组成、键合状态和石墨化程度,结合阻燃性能测试,揭示APP和ATH的协同阻燃机制。SEM分析表明相较于APP与ATH单独使用,TPU/APP/ATH炭层的空洞结构更少,炭渣的致密性更高。XPS分析表明FR-TPU的炭渣中C元素含量相比于纯TPU有所降低,O元素的含量有所上升,其中TPU/APP10/ATH10的C元素含量从88.2%降至69.24%,O元素的含量从8.07%升至17.78%,P和Al元素含量相较于单独添加分别从11.74%和16.36%下降至3.91%和3.31%。在此基础上,通过对C元素的分峰拟合发现TPU炭渣中C—C/C—H,C—O/C—N和CO/CN含量分别为61.05%,35.65%和3.30%;TPU/APP10/ATH10炭渣中三种结构含量分别为45.38%,45.00%和9.63%,说明ATH和APP复配使用有利于C元素形成酯、醚、羰基、羧酸（盐）、酯基等结构。通过对O元素的分峰拟合发现,TPU炭渣中O₂/H₂O,—O—,O三种结构含量分别为28.75%,44.36%和26.89%;TPU/APP10/ATH10炭渣中O₂/H₂O,—O—,O三种结构含量分别为44.33%,32.78%和22.89%,说明APP和ATH的加入有利于炭渣中O元素形成O₂/H₂O结构。通过对N元素的分峰拟合发现,TPU炭渣中—NH—,N结构的N元素含量分别为40.93%和59.07%;TPU/APP10/ATH10中—NH—,N结构的N元素含量分别47.17%和52.83%,说明ATH与APP复配使用促进了—NH—结构的形成。拉曼测试表明,相比于单独使用,APP和ATH复配使用,炭层的石墨化程度更好,致密性更高。以上分析结合阻燃测试可以得出TPU/APP/ATH复合材料阻燃机制：ATH受热分解生成氧化铝,吸收热量并释放大量水蒸气,有效促进APP降解,生成不燃性的氨气和聚磷酸,氨气和水蒸气稀释可燃性气体的浓度。随着温度继续升高,氧化铝可继续与聚磷酸反应生成偏磷酸铝[Al(PO₃)₃],同步催化聚氨酯基体成炭,形成高度石墨化炭层,石墨化炭层与偏磷酸铝一起覆盖在基体表面,有效抑制燃烧区域物质以及能量的输运,从而达到阻燃目的。     

分散剂对YAG粉末形貌和性能的影响

以硝酸铝［Al(NO3)39H2O］和硝酸钇［Y(NO3)36H2O］为原料,碳酸氢铵［NH4HCO3］为沉淀剂,PEG400,PEG800和PEG1000等为分散剂,采用正向共沉淀法合成了钇铝石榴石（YAG）前驱体粉末。并用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、粒度测试仪等分析了粉末的形貌和性能。结果表明,分散剂的加入,减少了粉末的团聚现象,而且由PEG400,PEG800分散剂制备的先驱体粉末经1200 ℃煅烧60 min后均能形成纯度较高的YAG相,但PEG1000样品粒度更细,比表面积为1748.78 m2/kg,中位径为1.42 m,而前者所得粉末的比表面积分别为29.39和128.60 m2/kg,中位径分别为196.14和20.55 m。     

Facile Iron‐Mediated Dispersant‐Free Suspension Polymerization of Methyl Methacrylate via Reverse ATRP in Water

An iron‐mediated reverse ATRP of methyl methacrylate (MMA) is successfully carried out in water in the absence of any dispersants, using a water‐soluble 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) as the initiator and the stabilizer, and using an oil‐soluble N,N‐butyldithiocarbamate ferrum (Fe(S₂CN(C₄H₉)₂)₃) as the catalyst without adding any additional ligands. Micron‐sized PMMA particles with UV light‐sensitive ‐S₂CN(C₄H₉)₂ end group are obtained, and monomer droplet nucleation and suspension polymerization mechanism are proposed. Polymerization results demonstrated typical “living”/controlled characteristics of ATRP: first‐order polymerization kinetics, linear increase of molecular weights with monomer conversion and narrow molecular weight distributions for the resultant PMMA particles. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirm the attachment and livingness of UV light‐sensitive ‐S₂CN(C₄H₉)₂ group in the chain end.

     

Kinetics of adhesive contact formation between thermoplastic melts and solid surfaces: Effect on bond strength

Formation of an adhesive contact between a polymer melt (or solution) and reinforcing fibers is considered from the viewpoint of kinetics. A two-stage model of this process has been proposed, and an expression for the interfacial bond strength as a function of time and temperature is derived. Experimental data on bond strength in adhesive joints between thermoplastic polymers and reinforcing fibers formed under various conditions were obtained, and the concept of activation energy was used to analyze them. Since the process is controlled by the stage having the larger activation energy, the adhesive contact formation between fibers and polymer solutions is governed by the rate of adhesive bonding, whereas that between fibers and polymer melts is governed by the rate of the melt spreading.     

不同聚合物分散剂对Pt/SAPO-11催化剂性能的影响

采用浸渍法制备了经过不同聚合物分散剂处理的Pt/SAPO-11催化剂,并通过X射线衍射(XRD)、透射电子显微镜(TEM)、N₂吸附-脱附和NH₃程序升温脱附(TPD)等对催化剂的组织结构进行了表征。结果表明,分散剂不会破坏催化剂的结构,反而提高了其孔体积、孔径和比表面积,同时改变了沸石的酸强度和酸量,其中以聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂孔体积、孔径和酸性分布最佳。在固定床反应器上对不同分散剂处理的Pt/SAPO-11催化剂催化性能进行评价,结果表明聚乙烯吡咯烷酮处理的Pt/SAPO-11催化剂也表现出最佳的催化性能,麻风树油的加氢脱氧率高达99.45%,生物航空煤油组分收率和异构烷烃组分(C₈~C₁₆)的选择性分别达到了44.67%和56.37%。     

Multiblock Copolymers Based on Highly Crystalline Polyethylene and Soft Poly(ethylene-co-butadiene) Segments: Towards Polyolefin Thermoplastic Elastomers

Block copolymers based on polyethylene (PE) and ethylene butadiene rubber (EBR) were obtained by successive controlled coordinative chain transfer polymerization (CCTP) of a mixture of ethylene and butadiene (80/20) and pure ethylene. EBR-b-PE diblock copolymers were synthesized using the {Me₂Si(C₁₃H₈)₂Nd(BH₄)₂Li(THF)}₂ complex in combination with n-butyl,n-octyl magnesium (BOMAG) used as both the alkylating and chain transfer agent (CTA). Triblock and multiblock copolymers featuring highly semi-crystalline PE hard segments and soft EBR segments were further obtained by the development of a bimetallic CTA, the pentanediyl-1,5-di(magnesium bromide) (PDMB). These new block copolymers undergo crystallization-driven organization into lamellar structures and exhibit a variety of mechanical properties, including excellent extensibility and elastic recovery in the case of triblock and multiblock copolymers.