塑料异型材口模构型要素对挤出形变的影响

塑料异型材的挤出胀大及其引起的不规则挤出形变,是异型材挤出制品尺寸控制的难点所在。针对此类问题,采用有限元方法研究了典型异型材口模构型要素如T型口模分支立臂位置、90°夹角L型口模过渡区域转角、L型口模两臂夹角等对挤出形变和模流平衡的影响。结果表明,随T型口模分支立臂由挤出中心位置向右偏移,挤出后的型材挤出中心位置发生偏移,立臂顶端向右上变形,从而使得挤出形变加剧,需要在模具设计时将立臂顶端向挤出中心方向进行补偿。在90°夹角L型口模内外转角处设置过渡圆角,有助于模具出口处的模流平衡。L型异型材两臂夹角在挤出后变大,且初始设计夹角为60°和90°时变化较大,需要根据相关实验找出其初始设计夹角与挤出后的实际夹角对应关系,以便在模具设计过程中进行参照。上述研究结果对逆向挤出问题的求解、异型材挤出模具的设计和口模构型的确定有着一定的参考意义。     

Improving Properties of Poly(vinylidene fluoride) by Adding Expanded Graphite without Surface Modification via Water‐Assisted Mixing Extrusion

Expanded graphite (EG) is introduced into poly(vinylidene fluoride) (PVDF) by melt mixing extrusion with water injection. The results demonstrate that the unfunctionalized EG in composite prepared with water injection exbibits better dispersion than that in the one prepared without water injection due to the promoting role of water during extrusion. Thus, the PVDF/EG composite with loading of 4 wt% prepared by water‐assisted mixing extrusion (WAME) exhibits electrical conductivity of about three orders of magnitude higher than the neat PVDF and one order of magnitude higher than the one prepared without water injection. Comparing to the neat PVDF, the thermal conductivity of the composites prepared with and without water injection is increased by 101.5% and 75.0%, respectively. The introduced EG leads to increased Young’s modulus and tensile strength especially for the composite prepared by WAME. The present work indicates that WAME can promote the dispersion of EG in PVDF matrix without any extra functionalization.     

2A50铝合金等方形通道转角挤压工艺研究

通过等方形截面通道转角挤压试验,并借助有限元模拟等方法,对不同工艺路线挤压后的2A50铝合金试样硬度和裂纹的变化情况及机理进行了探讨,发现BA路线较其他工艺路线更具应用价值,为后续工艺试验的进行提供了有力的依据。     

食品挤压过程中水分的作用及变化研究进展

水分对挤压操作的顺利实施和最终产品特性的形成十分重要。本文综述水分在食品挤压过程中的运动变化,以及物料含水率对挤压过程系统参数和挤出产品特性的影响,最后分析目前研究存在的问题,指出进一步深入系统研究挤压过程中水分作用的必要性。     

Kinetic and rheokinetic study of dicarboxylic fatty acid chain extension using a dioxazoline coupling agent

A kinetic and rheokinetic study of the condensation reaction of a dicarboxylic fatty acid, Pripol®1009 (C36), and a dioxazoline coupling agent (1,3‐Phenylene)‐bis(2‐Oxazoline) (OO) was made. The kinetic study showed a similar reactivity of the two acid groups of C36 and also a similar reactivity of the two oxazoline groups of OO. The reaction kinetics can be described using a second‐order kinetic model. A kinetic constant k = 16.1 × 10⁻⁴ mol⁻¹ s⁻¹ at 156°C with an activation energy E_a = 80.6 kJ mol⁻¹ was calculated. A rheological evaluation of the reactants and the obtained polymers showed that the reactive system had Newtonian behavior during all the reaction times for shear rates lower than 100 s⁻¹. Using this kinetic modeling and measured viscosity evolution of the reactive system at different temperatures, rheokinetic models were proposed for viscosity evolution with the molar mass evolution of the synthesized polymer and the reaction time and conversion. Viscosity evolution of the reactive system during the first 10 min, corresponding to a typical mean residence time in reactive extrusion, were calculated using the proposed rheokinetic model. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1017–1024, 1999     

Toughened composites prepared from castor oil based polyurethane and soy dreg by a one‐step reactive extrusion process

A series of water‐resistant composites were successfully prepared from a mixture of soy dreg (SD), castor oil, and 2,4‐toluene diisocyanate (TDI) by a one‐step reactive extrusion (REX) process. The structure and properties of the composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile testing, and swelling experiments. The results indicated that the toughness of the composites prepared from castor oil based polyurethane and SD was significantly improved. In this case, TDI played an in situ compatibilization role through the crosslinking reaction of ? NCO groups with ? NH₂, ? NH? , and ? OH groups in SD and castor oil. With an increase in the molar ratio of ? NCO groups of TDI and ? OH groups of castor oil, the degree of crosslinking, tensile strength, glass‐transition temperature, water resistivity, and solvent resistivity of the composites increased. With an increase in the SD content of the composites, the tensile strength and solvent resistivity of the composites increased because of the reinforcement of the cellulose component in SD. This work provided a simple and effective way of preparing SD‐based composites by a REX process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 953–960, 2006     

Synthesis and characterization of hindered‐phenol‐containing amine moieties as antioxidants for polypropylene copolymers

(4‐Ethylphenyl)‐3,5‐ditertiarybutyl‐4‐hydroxybenzylamine, 1‐phenyl‐4‐(3,5‐ditertiarybutyl‐4‐hydroxybenzyl)piperazine, and 1‐(3,5‐ditertiarybutyl‐4‐hydroxybenzyl)piperidine were synthesized and characterized, and their performance in polypropylene copolymer (PPCP) was tested by multiple extrusions in a Brabender plasticorder. The thermooxidative stability of PPCP was assessed by the measurement of oxidative induction time at 200 ± 1°C, and the thermal stability was assessed by observation of the change in the melt flow rate. A comparative study of the synthesized antioxidants with the commercially available antioxidant 2,6‐ditertiarybutyl‐4‐methylphenol was made. The presence of phenolic and amino groups influenced the performance of the antioxidants. The performance of the antioxidants influenced the thermal stability of the PPCP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1097–1103, 2004     

Monoclinic Zirconia Bodies by Thermoplastic Ceramic Extrusion

Two ultrafine, undoped ZrO₂ powders with median primary particle sizes of 9 and 25 nm were used to prepare ceramic suspensions for thermoplastic extrusion. The organic vehicle consisted of an industrial-grade poly(ethylene- co -vinyl acetate) (EVA) or polyethylene (PE-HD) and decanoic acid as a dispersing agent. The powder volume loadings achieved were 44% and 52% by volume for the two powders, respectively. The amount of dispersant needed was calculated from a new model based on available chemisorption sites on the powder surface. Mixing and extrusion were conducted using a conventional modular plastic processing unit. Green bodies were dewaxed up to 450°C in an inert atmosphere and sintered to full density in air at 1060° and 1100°C, respectively. Analysis of the ceramic phase content and the microstructure of the bodies is presented.     

基于单片机的PID温控系统在塑料挤出机中的应用

针对在塑料挤出过程中温度控制的重要性，介绍了一种新型的PID温度控制系统。该系统采用高性能单片机芯片，可以方便地对系统加热、冷却周期及PID的各个参数进行在线设定和修改，提高了塑料挤出机的温控精度。     

Effect of degree of polymerization on gelation and flow processability of poly(vinyl chloride)

The effect of degree of polymerization (DP) on the gelation and flow processability of poly(vinyl chloride) (PVC) was studied. Sheets with adjusted degree of gelation were prepared by rolling rigid pipe formulation suspension PVC compounds with DPs of 800, 1050 and 1300 by changing the milling temperature. Their degrees of gelation were measured with DSC and their capillary flow properties were measured with a capillary rheometer at 150, 170 and 190°C and the effect of DP on the relation between gelation and flow processabilities was studied. Because of the higher shearing heat during milling, the sample with the higher DP had a higher history temperature and thus tended to show a higher degree of gelation. The viscosity increased as the gelation increased. The dependency of viscosity on DP was higher at higher milling and extrusion temperatures and thus at a higher degree of gelation and a lower shear rate. This was assumed to be attributed to the more prominent uniform molecular flow as against the particle flow. The die swell increased with increasing the milling and extrusion temperatures and hence with increasing the gelation. A sample with a lower DP tended to show a larger die swell and this tendency was even more pronounced at the higher extrusion temperature. The melt fracture easily occurred when a sample with advanced gelation was extruded at low temperature. Whereas at low milling temperatures a sample with the lower DP showed a lower critical shear rate at onset of melt fracture, and thus easily generating melt fracture, at high milling temperatures it showed a higher critical shear rate and hence scarcely generated melt fracture. These experimental results were explained by the fact and concept that a sample with a lower DP shows a higher increase in the gelation during extrusion and/or the slighter feature of particle flow as against the uniform molecular flow at the same gelation level. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1915–1938, 2004