Phil Coates

In-process vibrational spectroscopy and ultrasound measurements in polymer melt extrusion

Spectroscopic techniques have the potential to provide powerful, molecular-specific, non-invasive measurements on polymers during melt processing operations. An exploration is reported of the application and assessment of sensitivity of in-process vibrational spectroscopy - on-line mid-infrared (MIR), on-line near-infrared (NIR), in-line NIR and in-line Raman - for monitoring of single screw extrusion of high-density polyethylene and polypropylene blends. These vibrational spectroscopic techniques are compared with novel in-line ultrasound velocity measurements, which were acquired simultaneously, to assess the sensitivity of each method to changes in blend composition and to explore the suitability for their use in real time process monitoring and control. © 2003 Elsevier Ltd. All rights reserved.

Solid phase processing of polymers

Solid phase processing of polymers , Solid phase processing of polymers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Micromoulding: process characteristics and product properties

Abstract Key aspects of the technology and challenges associated with the micromoulding process are discussed. The apparent shear and extensional viscosity behaviour of a polyacetal at high wall shear rates have been measured using inline capillary rheometry on a commercial micromoulding machine and a larger servoelectric injection moulding machine; the polymer behaved predictably at shear rates in excess of 106 s-1. Initial moulding trials indicated that a stepped plaque and 0·25 mm thick rectangular plaque mouldings filled in a satisfactory manner, but a thicker plaque cavity exhibited a jetting flow into the cavity. A data capture system capable of measuring multiple process dynamics at high sampling rates (up to 50 kHz per channel) allowed detailed process measurements taken during moulding of the stepped plaque moulding. Atomic force microscopy of the moulded products showed different surface finishes on each step of the stepped plaque moulding. Topography scans of the 0·25 mm thick rectangular plaque moulding showed that mould surface features with length scales of the order of a few micrometres were well replicated on the moulded product and the quality of the surface finish is dependent on the melt pressure during moulding.

Effect of hydroxyapatite morphology/surface area on the rheology and processability of hydroxyapatite filled polyethylene composites

The commercial success of hydroxyapatite (HA) filled polyethylene composite has generated growing interest in improving the processability of the composite. A number of synthetic procedures and post synthesis heat treatment of HA has lead to the availability of powders with widely varying morphological features. This paper addresses the effect of morphological features of HA on the rheology and processability of an injection-moulding grade HA-HDPE composite. The results showed that low surface area HA filled composite exhibited better injection processing characteristics through improved rheological responses. The effect of reducing the surface area of the filler is to require less polyethylene to wet the filler and allows more polyethylene to be involved in the flow processes. These changes reduced the temperatures and pressures required for successful processing.

Micromoulding: process measurements, product morphology and properties

Abstract The growth in Micro Electro-Mechanical Systems (MEMS) and demand for functional devices at smaller and smaller length scales has placed increasing demands on industry for product miniaturisation. Consequently, the micro-injection moulding (micromoulding) technology has evolved for the mass production of minute, intricate, polymer and composite components. Although there has been significant growth in the technology, there is little understanding of the effects of the process dynamics on product properties. This paper presents details of a programme of work conducted within these laboratories with the objectives of enhancing the understanding of polymer processing–property interaction. More particularly, the effects of microscale processing on the rheological, mechanical and tribological properties of engineering and commodity polymers, nanocomposites, metal and ceramic injection moulded feedstock and biomaterials are being explored. Simple analysis reveals that process conditions are potentially more severe on melts than those encountered during conventional moulding. High shear and rapid cooling rates combined with a large surface area to volume ratio may have a much greater influence over the resultant properties of a micromoulded product. A Battenfeld Microsystem50 micromoulding machine has been instrumented with a variety of sensors and data acquisition equipment, producing process data for a number of different cavity geometries. A novel microinjection compounding (MIC) machine has also been developed minimising the process stages and reducing material exposure to excessive residence times. This paper gives details of the effects of micromoulding process conditions on component surface morphology and mechanical properties measured using SEM, atomic force microscopy and nano-indentation techniques.

Preparation and in vivo efficient anti-infection property of GTR/GBR implant made by metronidazole loaded electrospun polycaprolactone nanofiber membrane.

Infection is the major reason of GTR/GBR membrane failure in clinical application. In this work, we developed GTR/GBR nanofiber membranes with localized drug delivery function to prevent infection. Metronidazole (MNA), an antibiotic, was successfully incorporated into electrospun polycaprolactone (PCL) nanofibers at different concentrations (0, 1, 5, 10, 20, 30, and 40 wt% polymer). To obtain the optimum anti-infection membrane, we systematically investigated the physical-chemical and mechanical properties of the nanofiber membranes with different drug contents. The interaction between PCL and MNA was identified by molecular dynamics simulation. MNA released in a controlled, sustained manner over 2 weeks and the antibacterial activity of the released MNA remained. The incorporation of MNA improved the hydrophilicity and in vitro biodegradation rate of PCL nanofibers. The nanofiber membranes allowed cells to adhere to and proliferate on them and showed excellent barrier function. The membrane loaded with 30% MNA had the best comprehensive properties. Analysis of subcutaneous implants demonstrated that MNA-loaded nanofibers evoked a less severe inflammatory response than pure PCL nanofibers. These results demonstrate the potential of MNA-loaded nanofiber membranes as GTR/GBR membrane with antibacterial and anti-inflammatory function for extensive biomedical applications.

Semi-automated image analysis of the true tensile drawing behaviour of polymers to large strains

An image analysis system has been developed using commercially available hardware with custom software to investigate the deformation behaviour of solid polymers in uniaxial tension. This technique provides a rapid, semi-automated non-contacting method for determining true process stress-strain-strain-rate behaviour for both homogeneous and inhomogeneous deformation. The relative displacements of printed transverse grid lines are determined from images captured during a standard monotonic tensile test, providing local measures of strain. The examination of a time series of images allows the generation of true strain-rate data, and concurrent monitoring of the total draw force from the load cell allows the generation of true stress data at those times when the images are captured. Therefore, it is possible to produce a series of process uniaxial true stress-strain curves for individual “elements” of material within the gauge length of the specimen. Synthetic elastomers drawn at ambient temperature have been found to display relatively homogeneous deformation, resulting in a simple process axial stress-strain curve for the single-speed test, whereas in the case of inhomogeneous deformation (“necking”) exhibited by polypropylene, it is verified that each element of material experiences a slightly different deformation process. This spatially variant deformation is related to the original location of the particular element with respect to the point of neck initiation.

Application of an elastic model to the large deformation, high temperature stretching of polypropylene

A physically based constitutive law for the deformation of polymers is applied to the stretching of polypropylene to large deformations at elevated temperatures. In this deformation regime, which is applicable to many forming processes, necking of the material is a persistent feature. The theory is elastic in nature, but includes the necking phenomenon as an inherent property. It is incorporated into a commercial finite element code and used to model a number of different experimental modes of deformation, both uniaxial and biaxial. Comparison is made with the experiments and it is found that both strains and forces are represented realistically, even though the true nature of the material is viscoelastic. Some of the discrepancies in the model predictions are traceable to its elastic nature.

In line melt temperature measurement during real time ultrasound monitoring of single screw extrusion

Abstract Ultrasonic velocity measurements provide process related information to complement conventional temperature and pressure measurements, since velocity varies with material type and with temperature and pressure conditions. The technique is non-invasive, can be applied directly to the process, and results are available in real time. An ultrasonic virtual instrument has been used on industrial scale extruders in house. Experimental results are presented, showing ultrasonic velocity to be a powerful tool for improving knowledge of polymer melt bulk temperature during extrusion.

Process monitoring of polymer melts using in-line spectroscopy

Over the last decade, there has been an increased drive in the polymer industry toward the development of in-line monitoring techniques for analysis of melt processing. Manufacture of high material volumes combined with stringent quality-control restrictions and the requirement for tailored end-user products, have made the implementation of analytical methods essential for measurement of material characteristics. This paper presents the application of a range of spectroscopic techniques for in-line analysis of polymer extrusion processes. Fourier transform near-infrared (FT-NIR), Raman and fluorescence spectroscopy have been successfully implemented as tools to monitor a range of processing characteristics including copolymer melt and additive composition, material residence time distribution and degree of polymerization. In combination with partial least squares (PLS) chemometric analysis, these spectroscopic techniques are demonstrated to be sensitive and robust tools for monitoring a wide range of chemical and physical parameters at high-temperature and pressure in a polymer-processing environment.