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Composites of Linear Low Density Polyethylene (LLDPE) and Graphene Nanoplatelets (GNPs) were processed using a twin screw extruder under different extrusion conditions. The effects of screw speed, feeder speed and GNP content on the electrical, thermal and mechanical properties of composites were investigated. The inclusion of GNPs in the matrix improved the thermal stability and conductivity by 2.7% and 43%, respectively. The electrical conductivity improved from 10-11 to 10-5 S/m at 150 rpm due to the high thermal stability of the GNPs and the formation of phonon and charge carrier networks in the polymer matrix. Higher extruder speeds result in a better distribution of the GNPs in the matrix and a significant increase in thermal stability and thermal conductivity. However, this effect is not significant for the electrical conductivity and tensile strength. The addition of GNPs increased the viscosity of the polymer, which will lead to higher processing power requirements. Increasing the extruder speed led to a reduction in viscosity, which is due to thermal degradation and/or chain scission. Thus, while high speeds result in better dispersions, the speed needs to be optimized to prevent detrimental impacts on the properties. 2016 The Authors. Published by Elsevier Ltd. This work was made possible by NPRP grant No. NPRP5-039-2-014 from the Qatar National Research Fund (A Member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors Scopus

The focus of this work is to develop the knowledge of prediction of the physical and chemical properties of processed linear low density polyethylene (LLDPE)/graphene nanoplatelets composites. Composites made from LLDPE reinforced with 1, 2, 4, 6, 8, and 10 wt% grade C graphene nanoplatelets (C-GNP) were processed in a twin screw extruder with three different screw speeds and feeder speeds (50, 100, and 150 rpm). These applied conditions are used to optimize the following properties: thermal conductivity, crystallization temperature, degradation temperature, and tensile strength while prediction of these properties was done through artificial neural network (ANN). The three first properties increased with increase in both screw speed and C-GNP content. The tensile strength reached a maximum value at 4 wt% C-GNP and a speed of 150 rpm as this represented the optimum condition for the stress transfer through the amorphous chains of the matrix to the C-GNP. ANN can be confidently used as a tool to predict the above material properties before investing in development programs and actual manufacturing, thus significantly saving money, time, and effort. 2016 P. Noorunnisa Khanam et al. Scopus

In this work, flexible and high-performance piezoresistive strain sensors were fabricated by simple layer-by-layer electrostatic self-assembly of carbon nanoparticles on commercial polyurethane (PU) sponges. It was shown that the sponge-based strain sensors exhibited obviously positive and negative piezoresistive characteristics under tensile and compressive strains, respectively. The alternate assembly of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) contributed to the construction of a more complete conductive network and significantly improved the sensing performance of the sensor due to the synergistic effect between CNTs and GNPs. Compared with the CNT@PU and CNT/GNP@PU sponge strain sensors, the CNT/GNP/CNT@PU sensor had a larger strain detection range and higher linearity. Besides, the CNT/GNP/CNT@PU sponge strain sensor showed high sensitivity (GF = 43,000 at 60% tensile strain and GF = −1.1 at 50% compressive strain), responsive capability to very small strain (0.05%) and outstanding stability during 3000 loading cycles. Due to its excellent sensing performance, the CNT/GNP/CNT@PU sensor enabled monitoring of various physiological activities, including finger movements, wrist bending and walking etc. In addition, a 5 × 5 sensor array based on the sponge-based strain sensor was prepared to achieve accurate identification of weight distribution. This study provides valuable information for the development of flexible strain sensors with high-performance and low-cost.

In this work, thermoplastic polyurethane based conductive polymer composites containing carbon nanotubes (CNTs) and synthesized silver nanoparticles (AgNPs) were used to fabricate highly elastic strain sensors via fused deposition modeling. The printability of the materials was improved with the introduction of the nanofillers, and the size and content of the AgNPs significantly influenced the sensing performance of the 3D printed sensors. When the CNTs:AgNPs weight ratio was 5:1, the sensors exhibited outstanding performance with high sensitivity (GF = 43260 at 250% strain), high linearity (R2 = 0.97 within 50% strain), fast response (~57 ms), and excellent repeatability (1000 cycles) due to synergistic effects. A modeling study based on the Simmons' tunneling theory was also undertaken to analyze the sensing mechanism. The sensor was applied to monitor diverse joint movements and facial motion, showing its potential for application in intelligent robots, prosthetics, and wearable devices where customizability are usually demanded.

Successful printing of high-performance material with suitable properties using additive manufacturing methods such as Fused Filament Fabrication (FFF) can create many advanced applications in industries. However, the high viscosity of high-performance polymers causes complications during the FFF process and reduces the final print quality. To overcome this challenge, Inorganic Fullerene Tungsten Sulphide (IF-WS2) nanoparticles are applied in this study to enhance the flowability of poly-ether-ketone-ketone (PEEK) without compromising its mechanical and thermal properties. In the first step, different loadings of IF-WS2 nanoparticles are melt compounded with PEEK and the nanocomposites are characterized. SEM and EDX images of fractured surfaces indicate that a good dispersion of nanoparticles is achieved without any pre-treatment or pre-dispersion. A reduction in melt viscosity of 25%, and a simultaneous growth in storage modulus, crystallization and degradation temperature of about 60%, 53% and 100 °C is found with addition of 2 wt% IF-WS2 to PEEK, respectively. This great achievement is mainly ascribed to the unique characteristics of IF-WS2 nanoparticles, acting as both reinforcing and lubricating agents, indicated by a reduction in coefficient of friction. There is no significant increase of crystallization and melting temperatures with the addition of IF-WS2 nanoparticles, which is beneficial in the FFF process. In the second step, the PEEK nanocomposite filaments are printed via FFF. The print quality and mechanical properties of the printed PEEK are also improved with the incorporation of IF-WS2 nanoparticles. Hence, incorporation of IF-WS2 nanoparticles into PEEK via melt compounding is an effective approach for the development of suitable high-performance engineering materials for FFF.

Multiwalled carbon nanotube (MWCNT)-doped polyamide 12 (PA12) films with various nanofiller loadings were prepared via a solution casting method to simultaneously improve the electrical conductivity and fracture toughness of carbon fiber/epoxy (CF/EP) composites. The films were interleaved between CF/EP prepreg layers and melted to bond with the matrix during the curing process. To improve the interfacial compatibility and adhesion between the conductive thermoplastic films (CTFs) and the epoxy matrix, the CTFs were perforated and then subjected to a low temperature oxygen plasma treatment before interleaving. Fourier transform infrared (FTIR) spectra results confirm that oxygen-containing functional groups were introduced on the surface of the CTFs, and experimental results demonstrate that the electrical conductivity of the laminates was significantly improved. There was a 2-fold increase in the transverse direction electrical conductivity of the laminate with 0.7 wt% MWCNT loading and a 21-fold increase in the through-thickness direction. Double cantilever beam (DCB) tests demonstrated that the Mode-I fracture toughness (GIC) and resistance (GIR) of the same laminates significantly increased by 59% and 113%, respectively. Enhancements of both interlaminar fracture toughness and electrical conductivity are mainly attributed to the strong interfacial adhesion achieved after plasma treatment and to the bridging effect of the carbon nanotubes.

This paper presents a multiscale computational homogenisation approach for the calculation of homogenised structural level mechanical properties of 3D textile/woven based fiber reinforced polymer (FRP) composites. Textile or woven composites, in which interlaced fibres are used as reinforcement, are a class of FRP composites which provide flexibility of design and functionality and are used in many engineering applications, including ships, aircrafts, automobiles, civil structures and prosthetics [1]. The more recently developed 3D-textile composites, consisting of 3D arrangements of yarns in a polymer matrix, allow weaving of near-net-shape and complex structures as compared to the traditional 2D-textile composites. In addition, these 3D-textile composites provide high through-thickness mechanical properties, lower manufacturing cost and improved impact and delamination resistance. The macro or structural level mechanical properties of these composites are rooted in their underlying complicated and heterogeneous micro structures. The heterogeneous microstructure of these composites requires a detailed multiscale computational homogenisation, which results in the macroscopic constitutive behaviour based on their microscopically heterogeneous representative volume elements (RVE). Elliptical cross sections and cubic splines are used respectively to model the cross sections and paths of the yarns within these RVEs. The RVE geometry along with other input parameters, e.g. material properties and boundary conditions, are modelled in CUBIT/Trelis using a parameterised Python script. The multiscale computational homogenisation scheme, with a unified imposition of RVE boundary conditions, is implemented in MoFEM (Mesh Oriented Finite Element Method) [2], which allows convenient switching between linear displacement, uniform traction and periodic boundary conditions. MoFEM utilises hierarchic basis functions [3], which permits the use of arbitrary order of approximation leading to accurate results for relatively coarse meshes. The matrix and yarns within the RVEs are modelled by considering isotropic and transversely isotropic materials models respectively. The principal direction of the yarns required for the transversely isotropic material model is calculated using a computationally inexpensive potential flow analysis along these yarns. Furthermore, the computational framework is designed to take advantage of distributed memory high-performance computing. The implementation and performance of the computational tool is demonstrated with a variety of 2.5D and 3D woven based FRP composites including 3D orthogonal interlock, 3D orthogonal layer-to-layer interlock, 3D orthogonal through-the-thickness angle interlock, 2.5D layer-to-layer angle interlock and 2.5D layer-layer angle interlock [4]. Keywords: Fiber reinforced polymer composites, 3D textile/woven composites, Finite element analysis, Multiscale computational homogenization. References: [1] Z. Ullah, Ł. Kaczmarczyk, S. A. Grammatikos, M. C. Evernden and C. J. Pearce (2016). Multi-scale computational homogenisation to predict the long-term durability of composite structures. Computers and Structures, 181 . pp. 21- 31. [3] Ł. Kaczmarczyk, Z. Ullah, K. Lewandowski, X. Meng, X. -Y. Zhou, I. Athanasiadis, I and C. J. Pearce (2017). MoFEM-v0.6.20. Zenodo. http://doi.org/10.5281/zenodo.1053811 [3] M. Ainsworth and J. Coyle (2003). Hierarchic finite element bases on unstructured tetrahedral meshes. International Journal for Numerical Methods in Engineering, 58 (14): 2103–2130, [4] Y. Rahali, M. Assidi, I. Goda, A. Zghal, and J. F. Ganghoffer (2016). Computation of the effective mechanical properties including nonclassical moduli of 2.5 D and 3D interlocks by micromechanical approaches. Composites Part B: Engineering, 98, 194-212.

Carbon fibre reinforced polymer composites offer significant improvement in overall material strength to weight, when compared with metals traditionally used in engineering. As a result, they are replacing metals where overall weight is a significant consideration, such as in the aerospace and automotive industries. However, due to their laminate structure, delamination is a prime concern. Through-thickness stitching has been shown to be a relatively simple method of improving resistance to delamination. In this paper, monofilament and multifilament fibres of a similar overall diameter were characterised and their properties compared for their suitability as stitching yarns. Dissimilar to other published works which rely on commercially available materials, such as polyparaphenylene terephthalamide, criteria were produced on the required properties and two potentially promising polymers were selected for extrusion. It was found that although the multifilament fibres had a greater ultimate tensile strength, they began to yield at a lower force than their monofilament equivalent. yes

Melt-mixed high density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) nanocomposites with 1–10 wt% MWCNTs were prepared by twin screw extrusion and compression moulded into sheet form. The compression moulded nanocomposites exhibit a 112% increase in modulus at a MWCNT loading of 4 wt%, and a low electrical percolation threshold of 1.9 wt%. Subsequently, uniaxial, sequential (seq-) biaxial and simultaneous (sim-) biaxial stretching of the virgin HDPE and nanocomposite sheets was conducted at different strain rates and stretching temperatures to investigate the processability of HDPE with the addition of nanotubes and the influence of deformation on the structure and final properties of nanocomposites. The results show that the processability of HDPE is improved under all the uniaxial and biaxial deformation conditions due to a strengthened strain hardening behaviour with the addition of MWCNTs. Extensional deformation is observed to disentangle nanotube agglomerates and the disentanglement degree is shown to depend on the stretching mode, strain rate and stretching temperatures applied. The disentanglement effectiveness is: uniaxial stretching < sim-biaxial stretching < seq-biaxial stretching, under the same deformation parameters. In sim-biaxial stretching, reducing the strain rate and stretching temperature can lead to more nanotube agglomerate breakup. Enhanced nanotube agglomerate disentanglement exhibits a positive effect on the mechanical properties and a negative effect on the electrical properties of the deformed nanocomposites. The ultimate stress of the composite containing 4 wt% MWCNTs increased by ∼492% after seq-biaxial stretching, while the resistivity increased by ∼1012 Ω cm.

Graphene, due to its outstanding properties, has become the topic of much research activity in recent years. Much of that work has been on a laboratory scale however, if we are to introduce graphene into real product applications it is necessary to examine how the material behaves under industrial processing conditions. In this paper the melt processing of polyamide 6/graphene nanoplatelet composites via twin screw extrusion is investigated and structure-property relationships are examined for mechanical and electrical properties. Graphene nanoplatelets (GNPs) with two aspect ratios (700 and 1000) were used in order to examine the influence of particle dimensions on composite properties. It was found that the introduction of GNPs had a nucleating effect on polyamide 6 (PA6) crystallization and substantially increased crystallinity by up to 120% for a 20% loading in PA6. A small increase in crystallinity was observed when extruder screw speed increased from 50 rpm to 200 rpm which could be attributed to better dispersion and more nucleation sites for crystallization. A maximum enhancement of 412% in Young's modulus was achieved at 20 wt% loading of GNPs. This is the highest reported enhancement in modulus achieved to date for a melt mixed thermoplastic/GNPs composite. A further result of importance here is that the modulus continued to increase as the loading of GNPs increased even at 20 wt% loading and results are in excellent agreement with theoretical predictions for modulus enhancement. Electrical percolation was achieved between 10-15 wt% loading for both aspect ratios of GNPs with an increase in conductivity of approximately 6 orders of magnitude compared to the unfilled PA6. Qatar National Research Fund - grant # [NPRP 5 - 039 - 2 - 014].

highlights � This paper discusses the energy conservation of an extruder. � This describes the energy and thermal efficiencies in polymer extrusion. � This explores the correlation between energy demand and thermal stability. � This explores radial temperature fluctuations of the melt flow in extrusion. � This models the total power demand in polymer extrusion empirically. abstract Thermal stability is of major importance in polymer extrusion, where product quality is dependent upon the level of melt homogeneity achieved by the extruder screw. Extrusion is an energy intensive process and optimisation of process energy usage while maintaining melt stability is necessary in order to pro- duce good quality product at low unit cost. Optimisation of process energy usage is timely as world energy prices have increased rapidly over the last few years. In the first part of this study, a general dis- cussion was made on the efficiency of an extruder. Then, an attempt was made to explore correlations between melt thermal stability and energy demand in polymer extrusion under different process settings and screw geometries. A commodity grade of polystyrene was extruded using a highly instrumented sin- gle screw extruder, equipped with energy consumption and melt temperature field measurement. More- over, the melt viscosity of the experimental material was observed by using an off-line rheometer. Results showed that specific energy demand of the extruder (i.e. energy for processing of unit mass of polymer) decreased with increasing throughput whilst fluctuation in energy demand also reduced. How- ever, the relationship between melt temperature and extruder throughput was found to be complex, with temperature varying with radial position across the melt flow. Moreover, the melt thermal stability dete- riorated as throughput was increased, meaning that a greater efficiency was achieved at the detriment of melt consistency. Extruder screw design also had a significant effect on the relationship between energy consumption and melt consistency. Overall, the relationship between the process energy demand and thermal stability seemed to be negatively correlated and also it was shown to be highly complex in nat- ure. Moreover, the level of process understanding achieved here can help to inform selection of equip- ment and setting of operating conditions to optimise both energy and thermal efficiencies in parallel. 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://

In this work, a highly instrumented single screw extruder has been used to study the effect of polymer rheology on the thermal efficiency of the extrusion process. Three different molecular weight grades of high density polyethylene (HDPE) were extruded at a range of conditions. Three geometries of extruder screws were used at several set temperatures and screw rotation speeds. The extruder was equipped with real-time quantification of energy consumption; thermal dynamics of the process were examined using thermocouple grid sensors at the entrance to the die. Results showed that polymer rheology had a significant effect on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. In particular, specific energy consumption was lower using a barrier flighted screw compared to single flighted screws at the same set conditions. These results highlight the complex nature of extrusion thermal dynamics and provide evidence that rheological properties of the polymer can significantly influence the thermal efficiency of the process.

Biaxial stretching of melt mixed high density polyethylene (HDPE)/multiwalled carbon nanotube (MWCNT) nanocomposites was conducted in the melt state at different stretching ratios (SRs). The addition of MWCNTs leads to significant strain hardening in the HDPE, greatly improving the stability and thus processability of the stretching process. Scanning electron microscopy shows that the MWCNTs in the polymer matrix are gradually disentangled and randomly oriented in the stretching plane with increasing SRs. All the stretched samples exhibit an increase in crystallinity (about 10%) due to strain induced crystallization and a broadened distribution of crystallite size according to the XRD and DSC results. The mechanical properties of the composites improve with increasing SRs, while they drop off after a SR of 2.5 for the neat HDPE which is likely to be due to the relaxation of polymer chains prior to solidification. The presence of the MWCNTs appears to inhibit this relaxation thus helping to maintain the orientation and mechanical properties at high SRs. The modulus, yield strength and breaking strength of stretched composites with 8 wt% MWCNTs increase by approximately 54%, 85% and 193% respectively compared with the neat HDPE at a SR of 3. The electrical percolation threshold for the unstretched material occurs at 1.9 wt% MWCNTs. As SR increases, the values of critical concentration increase from 1.9 wt% to 4.9 wt% implying the destruction of conductive networks due to an increased inter-particle distance. A loading of 6 wt% MWCNTs is sufficient to ensure that the sheet conductivity is robust to changes in the SR. Decreased values of critical exponent from 1.9 to 1.1 and morphological investigation reveal a transformation of the system structure from three dimensional to two dimensional as SR increases.

Polymer extrusion, in which a polymer is melted and conveyed to a mould or die, forms the basis of most polymer processing techniques. Extruders frequently run at non-optimised conditions and can account for 15–20% of overall process energy losses. In times of increasing energy efficiency such losses are a major concern for the industry. Product quality, which depends on the homogeneity and stability of the melt flow which in turn depends on melt temperature and screw speed, is also an issue of concern of processors. Gear pumps can be used to improve the stability of the production line, but the cost is usually high. Likewise it is possible to introduce energy meters but they also add to the capital cost of the machine. Advanced control incorporating soft sensing capabilities offers opportunities to this industry to improve both quality and energy efficiency. Due to strong correlations between the critical variables, such as the melt temperature and melt pressure, traditional decentralized PID (Proportional–Integral–Derivative) control is incapable of handling such processes if stricter product specifications are imposed or the material is changed from one batch to another. In this paper, new real-time energy monitoring methods have been introduced without the need to install power meters or develop data-driven models. The effects of process settings on energy efficiency and melt quality are then studied based on developed monitoring methods. Process variables include barrel heating temperature, water cooling temperature, and screw speed. Finally, a fuzzy logic controller is developed for a single screw extruder to achieve high melt quality. The resultant performance of the developed controller has shown it to be a satisfactory alternative to the expensive gear pump. Energy efficiency of the extruder can further be achieved by optimising the temperature settings. Experimental results from open-loop control and fuzzy control on a Killion 25 mm single screw extruder are presented to confirm the efficacy of the proposed approach.

Strain sensors based on conductive polymer composites have been widely investigated due to their excellent elasticity and sensitivity. Such sensors may be manufactured using additive manufacturing techniques but there are some challenges to overcome in terms of performance if this technique is to be used. In this work, a high-performance strain sensor of carbon nanotube/thermoplastic polyurethane (CNT/TPU) nanocomposites was printed by fused deposition modeling (FDM), and 1-pyrenecarboxylic acid (PCA) was introduced to non-covalently modify the CNTs and improve the polymer-nanofiller interactions. It is shown that the tensile and electrical properties of the modified composites are increased as a result of more uniform CNT dispersion. The 3D printed sensors demonstrate excellent properties with high gauge factor (GF = 117213 at a strain of 250%), large detectable strain (0–250%), good stability (up to 1000 loading/unloading cycles) and wide frequency response range of 0.01–1 Hz. Also, the strain sensing ability of the sensor is greatly improved with the introduction of PCA. The working mechanism of strain sensor was further studied based on the Simmons’ tunneling theory. In addition, the sensor demonstrates the capability to monitor human body movements and voice, showing its potential for applications in intelligent robots and wearable electronics where customizability is demanded.

Polymer extrusion is regarded as an energy-intensive production process, and the real-time monitoring of both energy consumption and melt quality has become necessary to meet new carbon regulations and survive in the highly competitive plastics market. The use of a power meter is a simple and easy way to monitor energy, but the cost can sometimes be high. On the other hand, viscosity is regarded as one of the key indicators of melt quality in the polymer extrusion process. Unfortunately, viscosity cannot be measured directly using current sensory technology. The employment of on-line, in-line or off-line rheometers is sometimes useful, but these instruments either involve signal delay or cause flow restrictions to the extrusion process, which is obviously not suitable for real-time monitoring and control in practice. In this paper, simple and accurate real-time energy monitoring methods are developed. This is achieved by looking inside the controller, and using control variables to calculate the power consumption. For viscosity monitoring, a ‘soft-sensor’ approach based on an RBF neural network model is developed. The model is obtained through a two-stage selection and differential evolution, enabling compact and accurate solutions for viscosity monitoring. The proposed monitoring methods were tested and validated on a Killion KTS-100 extruder, and the experimental results show high accuracy compared with traditional monitoring approaches.

Polymer extrusion is an energy intensive process, which is often run at less than optimal conditions. The extrusion process consists of gradual melting of solid polymer by thermal conduction and viscous shearing between a rotating screw and a barrel; as such it is highly dependent upon the frictional, thermal and rheological properties of the polymer. Extruder screw geometry and extrusion variables should ideally be tailored to suit the properties of individual polymers, but in practice this is rarely achieved due to the lack of understanding of the process. Here, in-process monitoring techniques have been used to characterise the thermal dynamics of the extrusion process. Novel thermocouple grid sensors have been used to measure melt temperature fields within flowing polymer melts at the entrance to an extruder die in conjunction with infra-red thermometers and real-time quantification of energy consumption. A commercial grade of polyethylene has been examined using three extruder screw geometries at different extrusion operating conditions to understand the process efficiency. Extruder screw geometry, screw rotation speed and set temperature were found to have a significant effect on the thermal homogeneity of the melt and process energy consumed.

The influence of annealing above the glass transition temperature (T(g)) on chain entanglement and molecular dynamics of solution-cast poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends was investigated via a combination of dynamic rheological measurement and broadband dielectric spectroscopy. Chain entanglement density increases when the annealing temperature and/or time increases, resulting from the increased efficiency of chain packing and entanglement recovery. The results of the annealing treatment without cooling revealed that the increase of the entanglement density occurred during the annealing process instead of the subsequent cooling procedure. Annealing above T(g) exerts a profound effect on segmental motion, including the transition temperature and dynamics. Namely, T(g) shifts to higher temperatures and the relaxation time (τ(max)) increases due to the increased entanglement density and decreased molecular mobility. Either T(g) or τ(max) approaches an equilibrium value gradually, corresponding to the equilibrium entanglement density that might be obtained through the theoretical predictions. However, no obvious distribution broadening is observed due to the unchanged heterogeneous dynamics. Furthermore, side group rotational motion could be freely achieved without overcoming the chain entanglement resistance. Hence, neither the dynamics nor the distribution width of the subglass relaxation (β- and γ-relaxation) processes is affected by chain entanglement resulting from annealing, indicating that the local environment of the segments is unchanged.

This review will summarize the significant body of research within the field of electrical methods of controlling the growth of microorganisms. We examine the progress from early work using current to kill bacteria in static fluids to more realistic treatment scenarios such as flow-through systems designed to imitate the human urinary tract. Additionally, the electrical enhancement of biocide and antibiotic efficacy will be examined alongside recent innovations including the biological applications of acoustic energy systems to prevent bacterial surface adherence. Particular attention will be paid to the electrical engineering aspects of previous work, such as electrode composition, quantitative electrical parameters and the conductive medium used. Scrutiny of published systems from an electrical engineering perspective will help to facilitate improved understanding of the methods, devices and mechanisms that have been effective in controlling bacteria, as well as providing insights and strategies to improve the performance of such systems and develop the next generation of antimicrobial bioelectric materials.

The development of nano-composite materials is making a significant impact on modern technology due to their wide range of applications and their superior properties1. Several methods have been proposed and developed to prepare polymer nano-composites. Graphene nano-composites, in particular, have attracted the interest of researchers because of their excellent properties, such as high electrical conductivity, high thermal stability and excellent mechanical strength 2–3. Graphene, a two-dimensional carbon atoms structure, exhibits exceptional properties4–5. Incorporating these nano-fillers with high performance polymers results in a unique combinations of properties.This paper reports on the synthesis and characterization of graphene and LLDPE (Linear Low Density Polyethylene)/graphene nano-composites with different weight ratios of graphene. Graphene was synthesized from graphene oxide, which was prepared by using modified hammers method. The obtained few layers of graphene were confirmed by different characterization methods such as FTIR, XRD, Raman spectroscopy and SEM. LLDPE/Graphene composites at different weight ratios of graphene, i.e. 1, 4, and 8 wt% were compounded in twin screw extruder. Extruded granules of LLDPE/Graphene materials were used in the preparation of nano-composites by compression molding. In this research, we used the LLDPE as the polymer matrix, because PE (polyethylene) is one of the most common plastic resins in the world and it is produced on a large scale in the State of Qatar by Qatar Petrochemical Company (QAPCO). LLDPE has grown most rapidly within the PE family due to its good balance of mechanical properties and process-ability compared to other types of PE. The effect of graphene ratio on the mechanical, thermal and electrical properties were investigated. LLDPE/Graphene composites with 4% graphene showed higher tensile strength and tensile modulus than the other graphene loading composites. Agglomeration was a problem in the composites with high wt% of the graphene which caused the reduction in tensile properties. Graphene marginally increased the melting temperature of the nano-composites whereas crystallization temperature, thermal stability and electrical conductivity were increased with increase of graphene loading. The results obtained showed that the graphene can increase the thermal stability of the polymer mixture. Increment of thermal stability is due to the high thermal stability of the graphene and the formation of phonon and charge carrier networks in the matrix. The electrical conductivity of LLDPE is 4.28 × 10− 11 and for nano composites is 9.2 × 10− 05. The high electrical conductivity of the graphene converts the LLDPE polymer insulator to an electrical conductor. Electrically conductive PE based composite materials can be used as electron magnetic-reflective materials, as well as in high voltage cables. The enhancement in mechanical, thermal and electrical properties of LLDPE/Graphene nano-composites achieved by melt mixing of graphene into the polymer can enable mass production of new and low cost novel materials with superior tensile strength, thermal stability and electrical conductivity.References1. Gossard Didier, Karkri Mustapha, Mariam A. AlMaadeed, Igor Krupa A new experimental device and inverse method to characterize thermal properties of composite phase change materials. Compos. Struct. 2015,133(1), 1149–1159.2. X. Huang, Z. Yin, S. Wu, X. Qi, Q. He, Q. Zhang, Q. Yan, F. Boey, H. Zhang. Graphene based materials: synthesis, characterization, properties and application. Smal. 2011, 18, 1876–1902.3. J.R. Potts, D.R. Dreyer, C.W. Bielawski, R.S. Ruoff. Graphene based polymer nanocomposites. Polymer 2011, 52, 5–25.4. T. Kulia, S. Bhadra, D. Yao, N.H. Kim, S. Bose, J.H. Lee. Recent advances in graphene based polymer composites. Prog. Polym. Sci. 2010, 35, 1350–1375.5. Du J, Cheng HM. The Fabrication, Properties and Uses of Graphene/Polymer Composites. Macromolecular Chemistry and Physics 2012;213:1060–1077.

The effect of different processing routes on structure and properties of high-density polyethylene (HDPE)-clay nanocomposites was assessed. Different compatibilizer/clay ratios (α) were also studied to determine if interactions exist between processing route and polymer-clay compatibility. HDPE/HDPE-g-MA/clay with α values of 1 to 4 were melt compounded (twin screw extrusion), and then processed via three routes: compression moulding, compression moulding followed by biaxial stretching or blown film extrusion. The structure was examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and oxygen barrier properties were determined. It was found that biaxial extensional forming produced the best enhancement in properties. An interaction between processing route and polymer-clay compatibility is evident. Halpin-Tsai (H-T) model was employed to predict relative modulus values. It showed good agreement with the experimental data. For biaxial extension at α = 4.0, the experimental relative modulus is greater than the predicted value. This may indicate the existence of a “nano” effect at the polymer-clay interface. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends with various compositions were prepared through solution casting and melt blending. Two preparation routes, solution casting and melt blending, were used to achieve different degrees of molecular entanglement in the samples with solution casting giving rise to a lower degree of entanglement. Therefore, the effect of molecular entanglement on molecular dynamics and phase-separation kinetics of PMMA/SMA blends was investigated by using broadband dielectric spectroscopy and small-angle laser light scattering (SALLS). Molecular entanglement is found to have a pronounced effect on the α -relaxation process. The glass transition temperature ( T g ) is related to the degree of entanglement and a higher degree of entanglement can result in a higher T g which shifts to a higher temperature after annealing. The relaxation time ( τ ) of the α -relaxation process is lower for lower degrees of entanglement. Neither the dynamics nor the distribution width of the β -relaxation process is affected by degree of entanglement, regardless of the blend composition. The kinetics of phase-separation by spinodal decomposition (SD) in PMMA/SMA blends are however significantly influenced by the degrees of entanglement with decomposition rate being higher at lower degrees of entanglement.

1949–2016Although Roy Crawford’s research extended to many areas of polymer engineering and science he will always be considered the father of rotational moulding research, such was his impact in t...

Nanocomposites of poly(ethylene terephthalate) PET with a partially synthetic fluoromica were prepared by melt mixing and extruded into sheet and subjected to large-scale biaxial stretching. Transmission electron microscopy (TEM) analysis of the mica tactoids showed that biaxial stretching had caused the tactoids to be more orientated and with improved exfoliation. The moduli of the nanocomposites were enhanced with increasing mica loading and the reinforcement effect was higher when the stretch ratio was 2 or 2.5, accommodated by having more aligned tactoids and reduced agglomeration. Enhancement in modulus was less pronounced for a stretch ratio of 3. Storage modulus was enhanced more significantly above the glass transition temperature. The barrier properties were enhanced by addition of mica before and after stretching. The Halpin-Tsai theory underpredicted the relative modulus of the PET nanocomposites, whereas the Nielsen model over-predicted the relative permeability. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

This article is concerned with understanding the behavior of polyethylene terephthalate (PET) in the injection stretch blow molding (ISBM) process where it is typically biaxially stretched to form bottles for the packaging industry. A comprehensive experimental study was undertaken, analyzing the behavior of three different grades of PET under constant width (CW), simultaneous (EB), and sequential (SQ) equal biaxial deformation. Experiments were carried out at temperature and strain rate ranges of 80–110°C and 1 s−1 to 32 s−1, respectively, to different stretch ratios. Results show that the biaxial deformation behavior of PET exhibits a strong dependency on forming temperature, strain rate, stretch ratio, deformation mode, and molecular weight. The tests were also monitored via a high speed thermal image camera which showed an increase in temperature between 5°C and 15°C depending on the stretch conditions. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 °C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal ‘ sea-island ’ structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous ‘ sea-island ’ structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area.

Summary: A novel methodology has been developed to describe the microstructure of polymer-clay nanocomposites quantitatively. It builds on the image analyses of transmission electron microscopy and optical microscopy micrographs, and two parameters, degree of dispersion and mean interparticle distance per unit volume of clay, are proposed to characterize the level of clay dispersion. It provides insights into the ‘real’ clay dispersion using a combination of both microscopical and macroscopical aspects.

The inclusion of a synthetic fluoromica clay in PET affects its processability via biaxial stretching and stretching temperature (95 °C and 102 °C) and strain rate (1 s−1 and 2 s−1) influence the structuring and properties of the stretched material. The inclusion of clay has little effect on the temperature operating window for the PET–clay but it has a major effect on deformation behaviour which will necessitate the use of much higher forming forces during processing. The strain hardening behaviour of both the filled and unfilled materials is well correlated with tensile strength and tensile modulus. Increasing the stretching temperature to reduce stretching forces has a detrimental effect on clay exfoliation, mechanical and O2 barrier properties. Increasing strain rate has a lesser effect on the strain hardening behaviour of the PET–clay compared with the pure PET and this is attributed to possible adiabatic heating in the PET–clay sample at the higher strain rate. The Halpin–Tsai model is shown to accurately predict the modulus enhancement of the PET–clay materials when a modified particle modulus rather than nominal clay modulus is used.

Polyamide and polystyrene particles were coated with titanium dioxide films by atomic layer deposition (ALD) and then melt-compounded to form polymer nanocomposites. The rheological properties of the ALD-created nanocomposite materials were characterized with a melt flow indexer, a melt flow spiral mould, and a rotational rheometer. The results suggest that the melt flow properties of polyamide nanocomposites were markedly better than those of pure polyamide and polystyrene nanocomposites. Such behavior was shown to originate in an uncontrollable decrease in the polyamide molecular weight, likely affected by a high thin-film impurity content, as shown in gel permeation chromatography (GPC) and scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer. Transmission electron microscope image showed that a thin film grew on both studied polymer particles, and that subsequent melt-compounding was successful, producing well dispersed ribbon-like titanium dioxide with the titanium dioxide filler content ranging from 0.06 to 1.12wt%. Even though we used nanofillers with a high aspect ratio, they had only a minor effect on the tensile and flexural properties of the polystyrene nanocomposites. The mechanical behavior of polyamide nanocomposites was more complex because of the molecular weight degradation. Our approach here to form polymeric nanocomposites is one way to tailor ceramic nanofillers and form homogenous polymer nanocomposites with minimal work-related risks in handling powder form nanofillers. However, further research is needed to gauge the commercial potential of ALD-created nanocomposite materials.

Semi-solid forming processes such as thermoforming and injection blow moulding are used to make much of today’s packaging. As for most packaging there is a drive to reduce product weight and improve properties such as barrier performance. Polymer nanocomposites offer the possibility of increased modulus (and hence potential product light weighting) as well as improved barrier properties and are the subject of much research attention. In this particular study, polypropylene–clay nanocomposite sheets produced via biaxial deformation are investigated and the structure of the nanocomposites is quantitatively determined in order to gain a better understanding of the influence of the composite structure on mechanical properties. Compression moulded sheets of polypropylene and polypropylene/Cloisite 15A nanocomposite (5 wt.%) were biaxially stretched to different stretching ratios, and then the structure of the nanocomposite was examined using XRD and TEM techniques. Different stretching ratios produced different degrees of exfoliation and orientation of the clay tactoids. The sheet properties were then investigated using DSC, DMTA, and tensile tests .It was found that regardless of the degree of exfoliation or orientation, the addition of clay has no effect on percentage crystallinity or melting temperature, but it has an effect on the crystallization temperature and on the crystal size distribution. DMTA and tensile tests show that both the degree of exfoliation and the degree of orientation positively correlate with the dynamic mechanical properties and the tensile properties of the sheet.

International audience; A 2D isothermal finite element simulation of the injection stretch-blow molding (ISBM) process for polyethylene terephthalate (PET) containers has been developed through the commercial finite element package ABAQUS/standard. In this work, the blowing air to inflate the PET preform was modeled through two different approaches: a direct pressure input (as measured in the blowing machine) and a constant mass flow rate input (based on a pressure-volume-time relationship). The results from these two approaches were validated against free blow and free stretch-blow experiments, which were instrumented and monitored through highspeed video. Results show that simulation using a constant mass flow rate approach gave a better prediction of volume vs. time curve and preform shape evolution when compared with the direct pressure approach and hence is more appropriate in modeling the preblowing stage in the injection stretch-blow molding process.

This paper presents a novel method to describe the microstructure of polymer/clay nanocomposites quantitatively. Based on the image analyses of transmission electron microscopy (TEM) and optical microscopy micrographs, two parameters, degree of dispersion (χ) and mean interparticle distance per unit volume of clay (λV) are proposed to describe the level of clay dispersion. The degree of dispersion gives the percentage of exfoliation, and λV is a measure of spatial separation between particles relative to clay loading. A polypropylene/clay system was chosen as an example to show the effects of processing conditions and biaxial stretching on clay dispersion using the proposed quantifiers. It provides insights into the ‘real’ clay dispersion using a combination of both microscopical and macroscopical aspects.

Solid-state NMR and TEM were used to quantitatively examine the evolution of clay morphology upon equibiaxial stretching of polypropylene/montmorillonite (PP−MMT) nanocomposites up to a stretch ratio (λ = final length/initial length) of 3.5. 1H spin−lattice relaxation times were measured by the saturation−recovery sequence. For the nanocomposites, initial portions of the magnetization recovery curves (≤∼20 ms) were found to depend on √t, indicative of diffusion-limited relaxation and in agreement with calculations based on estimates of the spin-diffusion barrier radius surrounding the paramagnetic centers in the clay, the electron−nucleus coupling constant, and the spin-diffusion coefficient. Initial slopes of these magnetization recovery curves directly correlated with the fraction of clay/polymer interface. New clay surface was exposed as a near linear function of strain. Long-time portions of the magnetization recovery curves yielded information on the average interparticle separations, which decreased...

Polymer nanocomposites offer the potential of enhanced properties such as increased modulus and barrier properties to the end user. Much work has been carried out on the effects of extrusion conditions on melt processed nanocomposites but very little research has been conducted on the use of polymer nanocomposites in semi-solid forming processes such as thermoforming and injection blow molding. These processes are used to make much of today’s packaging, and any improvements in performance such as possible lightweighting due to increased modulus would bring significant benefits both economically and environmentally. The work described here looks at the biaxial deformation of polypropylene–clay nanocomposites under industrial forming conditions in order to determine if the presence of clay affects processability, structure and mechanical properties of the stretched material. Melt compounded polypropylene/clay composites in sheet form were biaxially stretched at a variety of processing conditions to examine the effect of high temperature, high strain and high strain rate processing on sheet structure and properties. A biaxial test rig was used to carry out the testing which imposed conditions on the sheet that are representative of those applied in injection blow molding and thermoforming. Results show that the presence of clay increases the yield stress relative to the unfilled material at typical processing temperatures and that the sensitivity of the yield stress to temperature is greater for the filled material. The stretching process is found to have a significant effect on the delamination and alignment of clay particles (as observed by TEM) and on yield stress and elongation at break of the stretched sheet.

BACKGROUND: Poly(ethylene terephthalate) (PET) is widely used in the packaging industry. In order to enhance the mechanical and barrier properties, nanoscale fillers are added to PET matrices to form nanocomposites. In the work reported here, a melt-processed PET/synthetic mica nanocomposite sheet was characterised to determine the effect of the incorporation of synthetic mica on the sheet properties and also to see if these properties are an indicator of subsequent performance under high-speed, high-temperature biaxial deformation, typical of processes such as stretch blow moulding. RESULTS: The incorporation of synthetic mica was found to enhance the modulus, particularly above the glass transition temperature, and barrier properties of the extruded sheet and it significantly altered the deformation behaviour of PET under biaxial deformation. The plastic flow of PET during biaxial deformation was found to diminish for the nanocomposites, and strain hardening occurred earlier. CONCLUSION: The modulus and barrier properties of PET were enhanced by the incorporation of synthetic mica. Clay loading also altered the biaxial deformation behaviour of PET

Rotational molding is a process used to manufacture hollow plastic products, and has been heralded as a molding method with great potential. Reduction of cycle times is an important issue for the rotational molding industry, addressing a significant disadvantage of the process. Previous attempts to reduce cycle times have addressed surface enhanced molds, internal pressure, internal cooling, water spray cooling, and higher oven air flow rates within the existing process. This article explores the potential benefits of these cycle time reduction techniques, and combinations of them. Recommendations on a best practice combination are made, based on experimental observations and resulting product quality. Applying the proposed molding conditions (i.e., a combination of surface-enhanced molds, higher oven flow rates, internal mold pressure, and water spray cooling), cycle time reductions of up to 70% were achieved. Such savings are very significant, inviting the rotomolding community to incorporate these techniques efficiently in an industrial setting.

Poly(ɛ-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 °C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, molecular weight (Mw), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C3H10T1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive.

TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching and stretch ratio on the exfoliation and other tactoid properties. Though XRD spectra did not show any evidence of exfoliation, TEM image analysis revealed 10% exfoliation of clay platelets in the unstretched sheets. Stretching further improved the exfoliation as the concentration of thinner tactoids in the matrix increased due to stretching. Stretching also caused an increase in the concentration of longer tactoids and tactoids having higher aspect ratio, the reason for which was assumed to be due to the slippage of the platelets while stretching. It was found that stretch ratio affected the nanocomposite properties as increase in stretch ratio improved the exfoliation of clay platelets. Equi-biaxial stretching imparted preferential orientation of the tactoids in the matrix. Dynamic mechanical and barrier property measurements confirmed the observations made by the TEM image analysis.

This paper provides an overview of research on modelling of the structure-property interactions of polymer nanocomposites in manufacturing processes (stretch blow moulding and thermoforming) involving large-strain biaxial stretching of relatively thin sheets, aimed at developing computer modelling tools to help producers of materials, product designers and manufacturers exploit these materials to the full, much more quickly than could be done by experimental methods alone. The exemplar systems studied are polypropylene and polyester terephalate, with nanoclays. These were compounded and extruded into 2mm thick sheet which was then biaxially stretched at 155°C for the PP and 90 to 100°C for the PET. Mechanical properties were determined for the unstretched and stretched materials, together with TEM and XRD studies of structure. Multi-scale modelling, using representative volume elements is used to model the properties of these products. © 2008 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute.

Thermoforming is a polymer processing technique in which an extruded sheet is heated to its softening temperature and then deformed through the application of mechanical stretching and/or pressure into a final shape. The stretching operation is often performed by the movement of a mechanical plug, which contacts some areas of the sheet. During contact it is known that conductive heat transfer between the plug and sheet materials is an important factor in determining the process output. Attempts are currently being made to build realistic simulations of the thermoforming process and it is therefore extremely important that these heat transfer effects are included. However, the measurement of thermal contact conductance (TCC) between polymer pairs is extremely difficult in practice and there are no published values in literature. In this study, an axial conductive heat flow test rig has been developed and used to measure the TCC between contacting polymer pairs. Preliminary results between PVC and PTFE have shown that the value of thermal conductance is very small compared to published values for polymer/metal interfaces. Tests have also been carried out on Hytac®-B1X and PP. The TCC values were found to lie between 28.2-34.4 W/m 2 -K for average interface temperature between 45-75 °C. There was a slight increase in TCC with increasing interface temperature up to a temperature of about 70 °C. However, more experiments will be required to ascertain this. Further tests are being carried out to measure the TCC between different polymer pairs, and to assess the effects of variables such as surface roughness and contact pressure. These results will then be used to develop realistic models for contact heat transfer in thermoforming simulations.

This article reports on the results of ongoing work in which the foaming characteristics of metallocene-catalyzed linear low density polyethylenes for rotational molding are investigated. Earlier publications related rheological and thermal parameters to the polymer structure and mechanical properties and found that metallocene polyethylene can be used in rotational foam molding to produce a foam that will perform as well as a Ziegler-Natta catalyzed foam. Through adjustments to molding conditions, the significant processing and physical material parameters, which optimize metallocene catalyzed linear low-density polyethylene foam structure, have been identified. This article details the optimum processing route for the production of two layer skin/foam parts using the drop box method.

The structure and properties of melt mixed high-density polyethylene/multi-walled carbon nanotube (HDPE/MWCNT) composites processed by compression molding and blown film extrusion were investigated to assess the influence of processing route on properties. The addition of MWCNTs leads to a more elastic response during deformations that result in a more uniform thickness distribution in the blown films. Blown film composites exhibit better mechanical properties due to the enhanced orientation and disentanglement of MWCNTs. At a blow up ratio (BUR) of 3 the breaking strength and elongation in the machine direction of the film with 4 wt % MWCNTs are 239% and 1054% higher than those of compression molded (CM) samples. Resistivity of the composite films increases significantly with increasing BURs due to the destruction of conductive pathways. These pathways can be recovered partially using an appropriate annealing process. At 8 wt % MWCNTs, there is a sufficient density of nanotubes to maintain a robust network even at high BURs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42665.

High density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) composites containing 4 wt% MWCNTs were prepared by melt mixing followed by compression moulding into sheet. Compression moulded sheets were heated to just below the melting temperature and biaxially stretched at ratios (SRs) of 2, 2.5 and 3.0. The effect of stretching on the thermal and mechanical properties of the sheet was studied by differential scanning calorimetry (DSC) and tensile testing. DSC results show that the crystallinity of all the stretched samples increases by approximately 13% due to strain induced crystallization. The melting temperature of the biaxially stretched samples increases only slightly while crystallization temperature is not affected. Tensile test results indicate that at a SR of 2.5 the elastic modulus of the stretched composites increases by 17.6% relative to the virgin HDPE, but the breaking strength decreases by 33%. While the elastic modulus and breaking strength of the HDPE/MWCNT samples continue to increase as SR increases they drop off after a SR of 2.5 for the virgin HDPE. This is probably due to the constraining influence of the nanotubes preventing the relaxation of polymer chains caused by adiabatic heating at high SRs. The addition of MWCNTs results in significant strain hardening during deformation. While this will lead to increased energy requirement in forming it will also result in a more stable process and the ability to produce deep draw containers with more uniform wall thickness.

High density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by melt mixing using twin-screw extrusion. The extruded pellets were compression moulded at 200°C for 5min followed by cooling at different cooling rates (20°C/min and 300°C/min respectively) to produce sheets for characterization. Scanning electron microscopy (SEM) shows that the MWCNTs are uniformly dispersed in the HDPE. At 4 wt% addition of MWCNTs composite modulus increased by over 110% compared with the unfilled HDPE (regardless of the cooling rate). The yield strength of both unfilled and filled HDPE decreased after rapid cooling by about 10% due to a lower crystallinity and imperfect crystallites. The electrical percolation threshold of composites, irrespective of the cooling rate, is between a MWCNT concentration of 1∼2 wt%. Interestingly, the electrical resistivity of the rapidly cooled composite with 2 wt% MWCNTs is lower than that of the slowly cooled composites with the same MWCNT loading. This may be due to the lower crystallinity and smaller crystallites facilitating the formation of conductive pathways. This result may have significant implications for both process control and the tailoring of electrical conductivity in the manufacture of conductive HDPE/MWCNT nanocomposites.

Orthopaedic tissue engineering combines the application of scaffold materials, cells and the release of growth factors. It has been described as the science of persuading the body to reconstitute or repair tissues that have failed to regenerate or heal spontaneously. In the case of bone regeneration 3-D scaffolds are used as a framework to guide tissue regeneration. Mesenchymal cells obtained from the patient via biopsy are grown on biomaterials in vitro and then implanted at a desired site in the patient's body. Medical implants that encourage natural tissue regeneration are generally considered more desirable than metallic implants that may need to be removed by subsequent intervention. Numerous polymeric materials, from natural and artificial sources, are under investigation as substitutes for skeletal elements such as cartilage and bone. For bone regeneration, cells (obtained mainly from bone marrow aspirate or as primary cell outgrowths from bone biopsies) can be combined with biodegradable polymeric materials and/or ceramics and absorbed growth factors so that osteoinduction is facilitated together with osteoconduction; through the creation of bioactive rather than bioinert scaffold constructs. Relatively rapid biodegradation enables advantageous filling with natural tissue while loss of polymer strength before mass is disadvantageous. Innovative solutions are required to address this and other issues such as the biocompatibility of material surfaces and the use of appropriate scaffold topography and porosity to influence bone cell gene expression.

The present paper describes the results of an investigation into the modelling of plug assisted thermoforming. The objective of this work was to improve the finite element modelling of thermoforming through an enhanced understanding of the physical elements underlying the process. Experiments were carried out to measure the effects on output of changes in major parameters and simultaneously simple finite element models were constructed. The experimental results show that the process creates conflicting and interrelated contact friction and heat transfer effects that largely dictate the final wall thickness distribution. From the simulation work it was demonstrated that a high coefficient of friction and no heat transfer can give a good approximation of the actual wall thickness distribution. However, when conduction was added to the model the results for lower friction values were greatly improved. It was concluded that further work is necessary to provide realistic measurements and models for contact effects in thermoforming.

The present paper describes trials that were carried out on a conventional and a metallocene linear low density polyethylene to determine the effect of bubble content on the impact performance of rotationally moulded parts. Internal mould pressurisation was applied at different levels and at different internal air temperatures during the moulding cycle. The quantity of bubbles in the different mouldings was determined and related to impact performance at room temperature and at −40°C. Variations in dynamic mechanical properties were also highlighted.

As part of a study to characterise bioabsorbable scaffolds for tissue engineering an investigation has been conducted into the rate of degradation of polyglycolic acid (PGA). This is one of the most commonly used bioabsorbable materials and has been used in sutures since the 60s and more recently in cell scaffolds, drug delivery devices and bone fixation pins. This study looks at the influence that surface-to-volume ratio i.e. thickness of material, has on degradation. By degrading various thicknesses of PGA in a buffer saline solution over 24 days and testing their properties at regular intervals, a knowledge of how surface-to-volume ratio affects degradation was developed. Properties such as weight loss, crystallinity, molecular weight and structural integrity were measured. Results showed that rate of mass loss was dependent on sample thickness but crystallinity, melting point and molecular weight were independent of thickness.

The cure of polydicyclopentadiene conducted by ring-opening metathesis polymerisation in the presence of a Grubbs catalyst was studied using non-invasive Raman spectroscopy. The spectra of the monomer precursor and polymerised product were fully characterised and all stages of polymerisation monitored. Because of the monomer's high reactivity, the cure process is adaptable to reaction injection moulding and reactive rotational moulding. The viscosity of the dicyclopentadiene undergoes a rapid change at the beginning of the polymerisation process and it is critical that the induction time of the viscosity increase is determined and controlled for successful manufacturing. The results from this work show non-invasive Raman spectroscopic monitoring to be an effective method for monitoring the degree of cure, paving the way for possible implementation of the technique as a method of real-time analysis for control and optimisation during reactive processing. Agreement is shown between Raman measurements and ultrasonic time of flight data acquired during the initial induction period of the curing process.