Thermodynamically equilibrium roton states of nanoparticles in molten and vapour phases

We show a possibility for a thermodynamically equilibrium nanocrystalline structure consisting of nanosized solid inclusions to appear in a melt just beyond the melting curve. Thermodynamic stability of the nanocrystalline structure in the melt results from the free energy lowering due to rotational motion of nanoparticles. The main contribution to the reduction of the free energy of the system is due to an increase in the rotational entropy and change in formation energy of nanocrystals, i.e. the nanocrystalline structure in the melt, like vacancies in a crystal, is an equilibrium defect structure of the melt. It is demonstrated that similar nanocrystalline structures can also appear in the vapour phase in the form of liquid nanodrops and in liquid solutions, e.g. in He II.     

Device for non-disruptive taking of melt samples from a compounding process and direct injection molding

A concept for taking a sample from a polymer melt stream plus the direct processing of this melt to specimen is presented. Therefore, a melt sampling and direct injection molding (MSIM) device was developed. Process parameters were studied and the set-up was implemented successfully. Using the MSIM device, different thermoplastics were processed and provided specimen characterized. The mechanical material properties from samples of the MSIM process show a good consistency compared with data from conventional processes. The MSIM device can be used in production processes for quality control, e.g. color or mechanical properties, as well as in the field of research and development to reduce development cycles.     

Fire performances of unvulcanized rubbers and influences of horizontal flowing melts

Fire performances of typical unvulcanized rubbers are investigated and the properties of rubbers and their flowing melts are characterized. If the horizontal melt flow is allowed the burning area increases by 75%–473% and proportionally the peak mass loss rate promotes by 55%–300%. When the rubber converts to its flowing melt the viscosity and heat of complete combustion reduce, and the total crosslink density increases, which might be ascribed to the curing, the curing reversion and the decomposition mechanism. Except for acrylonitrile-butadiene rubber both the T_d,5% and the decomposition activation energy decrease. The pool fire development is related with the melt viscosity, the decomposition temperature and heat release rate (HRR) in the cone calorimeter. Low viscosity contributes to large pool area. High HRR and low decomposition temperature accelerate the extension of burning area.     

烯丙基化碳纳米管改善丙烯酸酯压敏胶的性能

本文利用γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH570)对多壁碳纳米管(MWNTs)进行修饰使其表面接枝上烯丙基官能团,与丙烯酸酯类单体进行原位聚合,制备了一种耐高温丙烯酸酯压敏胶(PSA)。 通过傅里叶变换红外光谱仪(FT-IR)、热重分析仪(TGA)和扫描电子显微镜(SEM)表征了MWNTs和丙烯酸酯PSA的结构与性能,探讨了改性MWNTs的质量分数对PSA耐热性能和粘接性能的影响。 结果表明,与未改性的丙烯酸酯PSA相比,当改性MWNTs的质量分数为1.5%时,改性丙烯酸酯PSA的耐热性能和粘接性能最佳,热分解温度从360 ℃提高到了382 ℃,耐热温度从80 ℃提高到了155 ℃,初粘力、持粘力和180°剥离强度分别从2 h和13.66 N/(25 mm)(12号小球)提高到了27 h和17.34 N/(25 mm)(17号小球)。     

Poly(propylene carbonate)/poly(3‐hydroxybutyrate)‐based bionanocomposites reinforced with cellulose nanocrystal for potential application as a packaging material

Poly(propylene carbonate) (PPC) is an aliphatic polycarbonate synthesized from carbon dioxide and propylene oxide. Poly(3‐hydroxybutyrate) (PHB) is a type of thermoplastic polyester produced by biological fermentation. The blending of PHB with PPC can effectively enhance the mechanical properties and barrier properties of PPC. Bionanocomposites of PPC/PHB enhanced by cellulose nanocrystal (CNC) are prepared via a two‐step process using polyethylene glycol as a carrier. Results show that the oxygen barrier properties of the composites increased with the increase of the CNC content. When the CNC content is 1 wt%, the oxygen barrier performance increases nearly 18 times. The assumed model can predict the barrier performance of composites with the combined influence of morphology and CNC distribution. This will make PPC/PHB/CNC nanocomposites a very promising degradable material for food packaging application.     

Poly(terephthalic anhydride) single crystals: Morphology and crystal structure

Single crystals of poly(terephthalic anhydride) (PTA) have been grown using the confined thin film melt polymerization technique. Thin lamellae (ca. 50 Å) are found for low polymerization temperatures, with thick crystals forming for polymerization at 200°C. Shearing of the material shortly after the initiation of polymerization at 200°C yielded single crystal domains composed of fibrillar texture material; these samples gave [010] zone ED patterns complementing the [001] zone patterns from the unsheared CTFMP samples. A monoclinic, single chain, two repeat unit, unit cell (Pc11) is proposed based on four different electron diffraction zone patterns: a = 6.01 Å, b = 3.94₅ Å, c = 14.11 Å, α = 106.9°. Simulations, using the Cerius² program, of the corresponding molecular conformation, packing and electron diffraction (ED) patterns were performed; the ED simulations are in good agreement with the observed patterns. An R-factor of 0.23 is obtained based on a comparison of calculated and observed structure factors for the 39 independent ED reflections observed on the different zone patterns. © 1996 John Wiley & Sons, Inc.     

Ring-opening polymerization of macrocyclic aryl ether ketone oligomers containing the 1,2-dibenzoylbenzene moiety

Facile ring-opening polymerization of cyclic aryl ether oligomers containing the 1,2-dibenzoylbenzene moiety to form high molecular weight linear polymers in the presence of a nucleophilic initiator is described. The polymerization can be initiated in the melt in the presence of a nucleophilic initiator such as potassium carbonate, cesium fluoride, and alkali phenoxides. Various alkali phenoxides were investigated as potential nucleophilic initiators. The polymerization reaction rate in the melt increases in the order of K⁺ > Na⁺ > Cs⁺, and in the order of ⁻OPhPhO⁻ > PhO⁻ > PhOPhO⁻ > PhPhO⁻. However, the polymerization in an aprotic dipolar solvent is faster in the presence of cesium phenoxide than in the presence of potassium phenoxide. Polymerization of the cyclic oligomers in solution demonstrates that the ring-opening polymerization proceeds via a chain-growth mechanism and involves a transetherification reaction between linear and cyclic aryl ether oligomers. The ring-chain equilibrium is much more favorable towards linear polymers. Since little or no ring strain exists in the cyclic system, the transetherification reactions are indiscriminate with regards to cyclic or linear chains and the interchain equilibration is also a facile process during polymerization. This intermolecular transetherification has been demonstrated by using low molecular weight aryl ethers to control the molecular weight of the polymer formed via ring-opening polymerization. © 1996 John Wiley & Sons, Inc.     

Synthesis of AB and ABA block copolymers as compatibilizers in nylon 6/polycarbonate blends

Nylon 6 (Ny6) and Bisphenol A polycarbonate (PC) are immiscible and form biphasic blends. To improve the compatibility of Ny6 and PC several ABA and AB Ny6/PC block copolymers were synthesized, and their compatibilizing behavior on the blends were tested. Block copolymers were prepared by reacting monoamino- or diamino-terminated Ny6 homopolymers with high molecular weight PC at 130°C in anhydrous DMSO. The reaction of diamino- and monoamino-terminated Ny6 with polycarbonate produces block copolymers of the type PC-Ny6-PC (ABA) and PC-Ny6 (AB), respectively, plus a certain amount of unconverted PC degradated to lower molecular weights. To separate the block copolymer from the unconverted PC, a selective fractionation with tetrahydrofuran (THF) and trifluoroethanol (TFE) was carried out. Three different fractions were obtained: THF-soluble fraction, TFE-soluble fraction, and the TFE-insoluble fraction. The scanning electron microscopy (SEM) analysis of a 75/25 (wt/wt) Ny6/PC blend added with 2% of ABA or AB block copolymers, showed the presence of smaller PC particles more adherent to the polyamide matrix, with respect to the same blend nonadded, which is clearly biphasic. The size of the PC particles decreases from ABA to AB compatibilized blends and the adhesion with the matrix is increases in the same way. © 1996 John Wiley & Sons, Inc.     

热塑性塑料熔体质量流动速率测量不确定度的评定

以聚乙烯为例讨论了热塑性塑料熔体质量流动速率测量不确定度的来源,依据JJF 1059-1999对熔体流动速率测试过程中的测量不确定度分量进行了分析和评定。7149型聚乙烯熔体质量流动速率测量结果的扩展不确定度为0.096 g/(10 m in)。