Study on preparation and reinforcement mechanism of high performance multi-walled carbon nanotube/ultra-high molecular weight polyethylene composite fibers

Daphne Tam¹, Shilun Ruan², Ping Gao¹, Tongxi Yu²

¹Department of Chemical Engineering, Hong Kong University of Science and Technology

²Department of Mechanical Engineering, Hong Kong University of Science and Technology

Ultrahigh molecular weight polyethylene (UHMWPE) has the simplest structure and in its fully extended form can have tensile modulus and tensile strength approaching theoretical estimation of ~200GPa and 19GPa respectively. However, there is a big gap between the mechanical properties of the current commercial PE fiber and the theoretical values [1-2]. In this study 5wt% acid-treated multi-walled carbon nanotube (MWCNT) have been adopted as the fillers and successfully developed a gel-spinning process using twins-extruder for fabricating highly oriented MWCNT/UHMWPE composite fibers. The modulus and the strength of the fibers enhance to 137 GPa and 4.2 GPa respectively, which are the best specific mechanical properties among the current commercial fibers.

An extensive experimental study was carried out to characterize the morphology and reinforcement mechanism of the highly oriented composite fibers. The mechanism of reinforcement has been studied using a combination of high resolution scanning electron microscopy and micro-Raman spectroscopy. Carbon nanotubes alignment along the tensile draw direction has been observed at high elongation ratios. Such alignment induces strong interfacial load transfer both at small and large strains to enhance the stiffness and tensile strength of the composite fiber. The detailed morphology of the fiber interface is studied using transmission electron microscopy. A direct observation of interface between the matrix and CNTs benefit our deeper understanding of the reinforcement mechanism.

Optimization of the extrusion process for recycling of commercial-grades of polyethylene terephthalate (PET) with minimal polymeric degradation

Mohammad Sagor Hosen¹, Heon Park² and Mark Staiger¹

¹Mechanical Engineering, University of Canterbury

²Chemical & Process Engineering, University of Canterbury

An extrusion-based 3D printing (3DP), fused deposition modelling (FDM), is proving to be a disruptive manufacturing as well as upcycling technology for semi-crystalline polymers. Extrusion of a recycled semi-crystalline polymer depends mainly on two properties, i.e., viscosity and degree of crystallinity. Thermal and mechanical degradation of polymeric chains during extrusion hampers the following extrusion cycles altering the viscosity and degree of crystallinity of the recycled semi-crystalline polymers. The purpose of this research is to optimize the thermal (temperature) and mechanical (shear stress and shear rate) parameters of the extrusion process for upcycling the semi-crystalline materials with minimal degradation. This study investigated the thermal (under Nitrogen) and oxidative (under air) degradation of the commercial-grades of PET using thermogravimetric analysis (TGA). The rheological analysis examined the viscosity at various temperatures and shear rates. Fourier-transform infrared (FTIR) spectroscopic analysis was used to identify molecular components and structures of various PET grades. Moreover, the melting temperature and the degree of crystallinity were measured using differential scanning calorimetry (DSC). TGA analysis shows significantly higher isothermal oxidative degradation starts from 260 oC under air than nitrogen environment. The rheological analysis exhibits a significant impact of temperature and shear rate on the viscosity of various grades of PET. Further studies on average molecular weight (Mw) and molecular weight distribution (MwD) measurement are needed to measure the polymeric degradation quantitatively.

Novel polymer material for wireless implantable sensors

Simon Blue¹, Deborah Munro¹

¹Mechanical Engineering, University of Canterbury

Current packaging choices for implantable wireless sensors have several limitations in terms of material selection, vapour permeability, biocompatibility, size, robustness, and lifetime. Packages based on metallic or ceramic enclosures guarantee mechanical and hermetic protection, therefore ensuring a long device lifetime, but they are limited in miniaturisation and flexibility. They are also opaque to electromagnetic waves, requiring the enclosed sensors to have battery sources of power and external antennas. Thus, universities and research institutions are exploring new polymer packaging materials to overcome these limitations.

The human body is a harsh environment: bodily fluids are highly conductive and contain many chemical and biochemical species that are potentially harmful to implanted electronic sensors. The packaging that encases the sensor directly interfaces with the body; therefore, it has to protect the sensor from bodily fluids while also protecting the body from any harmful effects from the sensor.

Polymeric packages, such as a liquid crystal polymer (LCP), offer mechanical flexibility, reduced size, weight and cost, biocompatibility, low vapour permeability, and hermetic seals. They can be injection moulded and are transparent to electromagnetic waves. This transparency allows for the transmission of wireless signals and/or power to an external device. However, LCP still has some drawbacks preventing its adoption for long-term applications. Although LCP has a low moisture absorption rate, the moisture from the human body will eventually pass through the packaging material, affecting the operation of the implanted electronic sensor.

Our research goal is to increase the lifetime and robustness of a polymer-based packaging technology that could provide an increased usable lifetime for an implanted sensor. This research project investigates using particulate deposition techniques, such as sputtering, to incorporate a thin impermeable metal membrane to improve the moisture barrier performance of an LCP package. Moisture ingress is monitored with a wireless, internal relative humidity sensor.

Rheological investigation of fatigue properties in brain tissue

Pavithran Devananthan¹, Rebecca Lilley¹, Natalia Kabaliuk¹, Paul Docherty¹

¹Mechanical Engineering, University of Canterbury

Mild traumatic brain injuries (mTBIs) in sports are an increasingly common occurrence. However, the understanding of the long term health effects of repetitive (mild) traumatic brain injuries (rTBIs) are lacking. . This study aimed to investigate the rheological and fatigue characteristics of brain tissue in cyclic loading representative of rTBIs. The rheological testing of ex-vivo ovine brain tissue in rotational shear with an amplitude sweep from 0.1% to 100%, and back to 0.1%, frequency of 3Hz and 20Hz for a set number of cycles was carried out. The. The stress strain response of the tissue, hysteresis and tissue viscoelastic properties were analysed. The effects of sample preparation, preloading and moisturization were analysed. After implementation of several procedural changes, the results were an increase in consistency of the measured storage and loss moduli, and hysteresis loops across the brain tissue samples.