Effect of temperature and mixing conditions on quality and consistency of poly(methyl methacrylate) bone cement

Abstract

The mixing of poly(methyl methacrylate) (PMMA) bone cement has been studied to develop methods for preparing a consistently high quality cement. A novel droplet test experimental procedure was developed that characterised the wetting characteristics involved in bone cement mixing. Using this technique it was established that increased wetting occurred by mixing bone cement at a lower temperature (-28°C) than normal mixing at room temperature.

The effect of temperature on viscosity of the cement mix was also investigated. An increase in viscosity with mixing time was found for all temperatures (owing to dissolution of PMMA in the monomer). However, the rate of increase in viscosity was a function of the initial temperature of the cement components. Cooling of the components initially to -12·6°C resulted in a better mix than room temperature samples, due to the cooled components having more mixing time at a lower viscosity (less than 1000 cP).

Automated mixing of the cement was also investigated. A high speed ‘figure of eight’ mixing machine (Kerr^® Automix^TM computerised mixing dental amalgamator) was used in a comparison with traditional hand held mixing devices. The effect of initial component cooling was also investigated in the high speed unit and cement samples were analysed for porosity and homogeneity of mix (using scanning electron microscopy). Results indicate that the combined effects of low initial temperature and automated mixing produces a bone cement that is more homogeneous and of lower porosity than hand mixed cement.     

核／壳羧基乳液的合成,形态及流变性

本文研究了聚苯乙烯/聚(丙烯酸-2-乙基己酯-丙烯酸)核/壳型(?)基乳液的合成工艺,乳胶粒形态及乳液的流变性。实验结果表明,采用两阶段法制得的核/壳型羧基乳胶粒具有翻转结构,且其翻转结构不受引发剂浓度和搅拌速度的影响。还研究了丙烯酸的用量与加料方式,核/壳阶段比对乳液流变性的影响,结果表明采用梯度式分批滴加丙烯酸的方法,可得到具有碱增稠性的乳液。     

密炼机三段混炼工艺第一段的优化

对ＢＢ３７０型密炼机胎面胶三段混炼工艺第一段进行了优化试验。缩短塑炼时间，可提高混炼效率；减少一次空翻（压砣提起再压下），可使混炼较长时间保持在高剪切作用状态，对炭黑分散十分有利。采用这些优化措施后，既保证了混炼胶粘度，又提高了分散度，而且能量消耗并没有增大。     

Effect of the composition of structured rubber particles on the toughness of poly(methylmethacrylate)

Composite natural rubber (NR) and monodisperse poly(n-butylacrylate) (PBuA) based latex particles were tested as possible impact modifiers for a poly(methylmethacrylate) (PMMA) matrix. A continuous extrusion process was used for the incorporation of wet latexes directly into a twin-screw extruder. All latexes had been coated by a PMMA shell. Furthermore, polystyrene (PS) subinclusions were introduced into the NR core. The impact resistance of the prepared PMMA blends can be most effectively improved by NR particles containing a large weight fraction of compatibilising PMMA in the shell. The degree of crosslinking of the shell polymer has to be restricted. PBuA based latex particles of 180 nm in size are ineffective to toughen the PMMA matrix. The degree of grafting of the NR phase in core–shell particles containing PS subinclusions is not crucial. Scanning electron microscopy was used to analyse the failure processes in composite rubber particle toughened PMMA blends at fast (impact conditions) and slow (tensile testing) deformation speeds.     

MLJ—200型密炼机微机智能控制系统

介绍了MLJ－300型密炼机微机智能控制系统的主要作用;根据混炼过程功率曲线可初步分析判断现有混炼工艺的优缺点,具有全自动和半自动优化混炼工艺的作用;可在每批混炼胶混炼结束时给出混炼胶粘度（塑性值）和分散度的预测值,并可在预测的基础上实现控制,从而全部达到质量指标,控制系统对控制对象开放和控制过程的模糊设定方便了用户,提高了自动控制率。     

Poly (alpha-methylstyrene) as a processing aid for rigid poly (vinyl chloride)

Poly (alpha-methylstyrene) (PAMS) is a new approach to process improvement in rigid poly (vinyl chloride) (PVC)—the use of a low molecular weight polymer as a process aid. PAMS can reduce fusion time, melt viscosity and improve heat stability of rigid PVC compounds. The reduced melt viscosity allows the addition of fillers to PVC without adverse effect on extrusion rates. This polymer also improves the resistance to melt fracture and shear “burning” at high shear rates. When used within the optimum concentration range, physical properties such as tensile strength, Izod impact and heat distortion are maintained. In addition, PAMS gives, improved production rates in both pipe extrusion and injection molding processes without sacrifice in properties.     

Rheological behaviour of fresh cement pastes formulated from a Self Compacting Concrete (SCC)

Self Compacting Concrete (SCC) has a high flowability and can be placed without vibration. It is defined as a concrete that exhibits a high deformability and a good resistance to segregation. This kind of concrete is of great interest and has gained wide use especially in the case of difficult casting conditions such as heavily reinforced sections. From a rheological point of view, the use of a Viscosity Enhancing Admixture (VEA) along with an adequate superplasticizer content enables to ensure high deformability and stability. However, little is known about the interactions between superplasticizer and viscosity agent. Hence, we propose to study several cement pastes formulated from the original paste of a typical SCC mix. Depending on their rheological behaviour, these pastes will be used later to study the stability of coarse aggregates. The major aim of this paper is to show that empirical tests such as spread and flow time are suitable to characterise the rheological behaviour of cement pastes instead of more complex ones. Rheological properties, i.e. viscosity and shear yield stress, are well correlated with empirical test results in the range of flowable mixes. Moreover, the experimental program leads to emphasize the effects of the mixing procedure on the rhelogical properties of cement pastes. Finally, test results enable to underline the interactions between superplasticizer and Viscosity Enhancing Admixture used in designing Self Compacting Concrete.     

UHMWPE/PEG共混方式及配比对UHMWPE缠结行为及性能的影响

超高分子量聚乙烯（UHMWPE）是常用的高性能聚合物。由于高黏度的影响,极大地限制了其加工成型与应用。聚乙二醇（PEG）具有高流动性,被广泛用来改善UHMWPE的流变行为,但复合材料中添加相的分散效果对材料的性能有重要影响。采用干粉混合、溶液混合、熔融挤出共混等方式制备了不同配比UHMWPE/PEG复合材料。基于熔融拉伸实验研究了共混方式及配比对UHMWPE缠结行为及性能的影响。结果表明,PEG的加入降低了复合材料的链缠结密度。三种混合方式中,加入5%PEG时干粉混合与挤出混合解缠作用较明显,链缠结密度均降低26%左右。     

Mixing in reactive extrusion of low-density polyethylene melts: Linear vs. branched

The melt flows of linear low-density polyethylene (LLDPE) and branched low-density polyethylene (LDPE) have been compared in a fully intermeshing co-rotating twin-screw extruder. The polyethylene melts were selected in order to investigate the effects of the melt rheology on the mixing. Their shear vicosity curves are quite similar, but the LDPE has a markedly higher apparent extensional viscosity over a wide range of stretch rates. The stagger of the paddles in the mixing zone of the extruder creates axial pressure-driven axial flow can have significant extensional strain components. Residence time distributions obtained in the melt zones of the extruder with tracer dye reveal that the LDPE has a narrower residence time distribution than the LLDPE over a wide range of operating conditions. The axial dispersion for the LDPE is significantly lower than the axial dispersion for the LLDPE. This is attributed to the greater extensional viscosity of the LDPE. During the reactive extrusion process, solid maleic anhydride and polyethylene were added at the feed port but the peroxide provides better control of the crosslinking reaction. Residence time distributions measured for the chemically more reactive LLDPE melt indicate reduced levels of axial mixing with reaction. The reduction in mixing is due to a crosslinking reaction that occurs in parallel to the grafting reaction. This change in mixing is smaller than the difference in mixing between LDPE and LLDPE.     

基于多因素的混炼胶质量预测模型

根据密炼机胶料混炼流变理论和瞬时功率控制法等理论,基于填充因数、转子功率、转子转速、排胶温度和压砣压力5个因素建立混炼胶粘度预测模型.检验结果表明,门尼粘度预测值与实际值很接近,两者差的平均值为0.827,预测效果良好。     

粉煤灰掺量对天然盐渍土强度和变形的影响

选取天然盐渍土在不同粉煤灰配合比条件下进行三轴试验、压缩试验和溶陷试验,研究粉煤灰对天然盐渍土的改良特性规律。试验结果表明:同种类盐渍土在一定条件下,盐渍土的抗剪强度随着粉煤灰配合比的增加逐渐增加;粉煤灰可改良盐渍土的压缩特性,压缩系数变化较大的垂直压力在400kPa之前,粉煤灰掺量越多,改良效果越好。氯渍土的压缩系数较硫酸盐渍土小,相应的压缩模量较大;粉煤灰对天然盐渍土溶陷特性的改良存在峰值压力为400kPa,对于粉煤灰的配合比也存在一界限值,氯盐渍土的粉煤灰最优配合比为15%,亚硫酸盐渍土的粉煤灰最优配合比为20%。     

Combinatorial Ink-Jet Printer for Ceramics: Calibration

This article describes an ink-jet printer for the construction of combinatorial libraries and functionally graded ceramics. It can mix and print all possible compositions for high-throughput screening. The number of components is set by the number of mixing valves that deliver ceramic ink from pressurized reservoirs into a circulation chamber. Compositional control is by either complete or incremental change. Organic liquids and ceramic inks are used in a systematic three-stage calibration. The calibration protocol accounts for the effects of ink viscosity, reservoir pressure, valve-opening time, and temperature, but reveals unexpected segregation effects that occur in the ink after deposition.     

Experimental characterization and multi-scale modeling of mixing in static mixers. Part 2. Effect of viscosity and scale-up

Static micro-mixers are used in precipitation processes to avoid mixing limitations. The mixing performance of these mixers, which are used in this study to mix two streams of different viscosity, is characterized using competitive-parallel chemical reactions and computational fluid dynamics (CFD). This work is an extension of a previous paper where mixing of fluids with equal viscosity has been studied [Lindenberg, C., Schöll, J., Vicum, L., Brozio, J., Mazzotti, M., 2008. Experimental characterization and multi-scale modeling of mixing in static mixers. Chemical Engineering Science 63, 4135-4149]. It is found that the mixing performance in terms of reaction yield and mixing time decreases slightly with increasing viscosity ratio in a two jet vortex mixer (Roughton mixer). In the Y-mixer the trend is the same at low flow rates, but it is the opposite at large flow rates due to a symmetry breaking phenomenon. The Roughton mixer is scaled-up using the CFD model and a linear relationship between scale-up factor and mixing time is observed. Finally, it is shown that mixing times can be described satisfactorily as a function of velocity, jet diameter and viscosity.     

Thermally expandable microcapsules for polymer foaming—Relationship between expandability and viscoelasticity

A new thermally expandable microcapsule was developed for use with foaming polypropylene (PP) by injection molding and extrusion processes at operating temperatures above 200°C. The microcapsule consists of a blowing agent as the core and a shell polymer. The rheological properties of the shell polymer were controlled by a crosslinking agent to design the expandability and shrinkage. The effects of rheological properties on the expandability and the surface appearance of foam products were thoroughly investigated. It was found that storage modulus G′ and tan δ significantly affected the expandability and shrinkage and were controllable through crosslinking polymerization. Visual observation of batch foaming, rheological measurement, and experiments of foam injection molding and extrusion elucidated the existence of the optimal degree of crosslinking that could realize more than 30% density reduction while maintaining a smoothsurface at PP foam injection molding and extrusion. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Polymer blend de‐mixing and morphology development of immiscible polymer blends during tube flow

This work is an investigation of morphology and de‐mixing of polymer blends during melt flow through a tube. Morphology is the relative size, shape and location of each distinguishable phase present in a polymer blend. De‐mixing is the shear‐induced migration of different types of polymers away from each other during the flow. The ability to tailor de‐mixing during extrusion can potentially result in a new family of plastics waste recycling processes with mixed waste entering an extruder and separate streams of different polymer types leaving it. Also, control of morphology development can lead to the formation of layered structures without the need for two or more extruders and co‐extrusion. This work is directed at elucidating morphology development and de‐mixing of polymer blends in the most simple process design: melt flow through a tube. Shear‐induced migration was quantitatively shown in various polyethylene‐polypropylene, polypropylene‐nylon 6 and polyethylene‐nylon 6 blends. The migration observed was in accord with the hypothesis that the system tends to minimize its rate of energy dissipation for a fixed flow rate. The ratio of the viscosity of the dispersed phased to that of the continuous phase greatly influenced the morphology of polypropylene‐nylon 6 and polyethylenenylon 6 blends: a droplet‐dispersed phase structure occurred at a high viscosity ratio, whereas a multi‐layer structure resulted at viscosity ratios near unity. Shear‐induced deformation and coalescence contributed to formation of the multi‐layer structure.     

Reactive modification of polyethylene terephthalate with polyepoxides

In attempts to produce modified poldified polyethlene terephthalate (PET) ressins with improved rheology for applications requiring high viscosity and elasticity (e.g., lowdensity extrusion foaming, extrusion blow molding), a novel dimidodiepoxide of low molecular weight was evaluated aschain extender/branching ageent. Its reactivity was compared with that of an ethylene/glycidy1 methacrylate copolymer. The diepoxide showed higher reactivity than the copolymer and could be used at muchlower concentrations. The complex chain extension/degradation reactions occurring in the melt were followed in a batch mixer by torque changes, and by analyzing the prouducts for residual carboxy1 and hydroxy1 content, intrinsic viscosity, insoluble content and melt viscoelastic properties. The perliminary results of this work indicated an overall decrease in carboxy1 content, increase in hydroxy1 content, increase in intrinsic viscosity ans melt viscosity and storage modulus values depending on mixing time and the type and concentration of the additive. It is shown that under certain conditions. reaction of PET with less than 1 wt% diimidodiepoxide may produce materials with rheological characteristics similar to thouse of PET grades that are extrusion foamable by gas injection to low densities.     

The significance of capillary rheology testing temperature for predicting PVC extrudability

A rheological investigation of the saturated fatty acids as lubricants for PVC was made in a Sieglaff-McKelvey rheometer over a wide temperature range. Results reveal that with an increase in carbon chain, fatty acids became more effective in reducing the melt viscosity of PVC. It was also discovered that the maximum viscosity variation due to these materials was observed at 350°F. At test temperatures of 400°F and above, no major viscosity differences were observed. Furthermore, the changes in the melt viscosity were more pronounced at shear rates less than 200 sec^?1. The usefulness of the measured viscosity variations at the critical test temperature of 350°F was shown by extrusion. An excellent correlation between the apparent melt viscosity and extrusion melt temperature was found. The criticalness of the test temperature in assessing the effect of lubricants on PVC flow is discussed.     

湿法喷涂料的研制

以铝矾土、棕刚玉、氧化铝微粉、硅微粉和铝酸钙水泥为原料制备了湿法喷涂料,对比分析了湿法喷涂料与干法喷涂料的物理性能,结果表明：湿法喷涂料的性能优于干法喷涂料,并且该湿法喷涂料施工环境优良,无粉尘危害,可替代干法喷涂料应用于水泥窑的衬里部位,使用效果良好。     

Polyethlene-modified bitumen for paving applications

In cold regions, transverse cracking of asphaltic paving materials is a serious problem which has not been completely resolved despite much effort. In this investigation, the low temperature stress–strain properties of bitumen containing dispersed polyethylene were measured over the temperature range from ?40 to 0°C and compared with unmodified bitumen in an attempt to develop a tougher, more ductile crack-resistant binder for paving materials. Several grades of polyethylene were individually dispersed in liquid, heated bitumen to produce therein colloidal suspensions of polyethylene. The viscosities of these suspensions were determined at various temperatures and concentrations for each grade of polyethylene. Despite rather large differences in composition, molecular weight, and crystallinity of the polyethylenes, the differences in viscosity at the same concentration were relatively minor. However, the viscosity was very sensitive to the polyethylene concentration and the mixture became difficult to process at concentrations greater than 10 percent by weight. Thesee hot mixtures were then cast into rectangular beams for flexural testing at temperatures below zero degrees Celsius. Near the optimum polyethylene concentration of 8 percent by weight, the bitumen mixture possessed increased flexural strength, increased flexural modulus, increased elongation, and increased fracture energ at temperatures near ?30°C. In one example the energy to fracture was increased ninefold compared to a standard 80/100 pen. bitumen control at ?20°C. Mix design results are presented for a typical aggregate and compared with a MTC HL4 hot-mix paving formulation which is used extensively throughout Ontario. The polyethylene-modified asphalt concrete mix displayed a curious increases in both the Marshall flow and the Marshall stability values. Dynamic mechanical measurements confirmed the expected increase in resilient modulus at temperatures above zero degrees Celsius. The Marshall briquets containing polyethylene also exhibited slightly greater wet strength retention after prolonged immersion in water. These observations are consistent with the published data for commercial Novophalt paving materials developed in Austria and predict that the use of polyethylene in asphaltic hot-mix paving materials can extend service temperature range at both high and low temperatures, thereby simultaneously reducing both pavement distortion (rutting) and low-temperature cracking, so that pavement lifetimes can be more than doubled. The cost of such modification can be substantially reduced if scrap or reclaim polyethylene is employed instead of virgin polyethylene. Dispersing agents, such as Shell Chemical Kraton G block copolymers were advantageously employed to control the emulsion stability, particle size, and compatibility of the dispersed polyethylene phase.     

Interfacial instabilities in multimaterial co-injection mouldings: Part 2 - Interfacial mixing in transparent mouldings

Abstract

Previous research in co-injection moulding has produced viscosity ratio guidelines for skin and core components, which must be followed if good core distribution is to be achieved. However, by examining two phase systems of PMMA-PC, which fall within the recommended viscosity range, this work shows that viscosity matching of materials is not a sufficient requirement for interfacial stability. The transparency of the materials allows areas of interfacial mixing to show up as streaks in the mouldings, so that factors affecting stability can be determined. One system is found to be more stable than the others. Explanations for such effects are given by consideration of interfacial mixing, viscosity, tooling geometry, injection speeds, interfacial stresses and shear in multilayered mouldings.