R.J.T. Lin

Contribution of Coalescence to Microfibril Formation in Polymer Blends during Cold Drawing

The main goal of this study is to obtain a morphological confirmation of the contribution of coalescence to the fibril formation mechanism in microfibril reinforced composites (MFC) and in this way to explain the large differences in sizes of the starting spheres and the resulting long microfibrils, at rather modest draw ratios (between 6 and 12). For this purpose, the peculiar property of compatibilizers has been exploited, namely coating the dispersed particles and thus preventing them from eventual coalescing after coming in contact. Using scanning electron microscopy (SEM) on samples at various stages of the cold drawing of polypropylene/poly(ethylene terephthalate) blends with and without a compatibilizer, the assumed mechanism has been established: the MFC from compatibilized blends show much shorter microfibrils because the compatibilizer inhibits the coalescence process. A qualitative model illustrating the transformation of the dispersed spheres into microfibrils due to coalescence during the cold drawing is also discussed. In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.

Machinability Investigation of Medium-Density Fibreboard

Abstract For many applications, the perceived quality of a medium-density fibreboard (MDF) is influenced by the appearance of its machined surface. The behaviour of MDF has been studied by passing a cutting tool through it at a relatively low speed. A digital camera was used that travels synchronously with the tool and the deformation occurring in front of the tool tip was recorded. The magnification of approximately 30× also allows the individual fibres or bundles to be clearly observed. Photographic images have also been taken of the same machining process at a much higher speed, producing similar results and thus establishing the slow-speed study as a viable option. The machining of different MDF samples has been recorded using a cutting speed of 1.6 mm s−1 and varying depths of cut (0.5, 0.75 and 1.0 mm). The video recordings of various panels permit the identification of their peculiar machining characteristics. Unrefined particles play a major role during machining. The trends of results have also been confirmed by scanning electron micrographs. The board densities were found to have a major influence on the machinability characteristics of the boards.

Experimental Study of Machinability of GFRP Composites by End Milling

This article describes an experimental investigation on end milling of glass fiber reinforced polymer (GFRP) composites using uncoated tungsten carbide tool. A series of experiments were carried out to evaluate the machinability of GFRP composites in terms of tool wear, tool useful life, machining quality, and machining forces. Machinability data were evaluated in the form of Taylors equation in order to predict the tool performance while machining this composite material. The useful life of the cutting tool was found to be well described by the Taylors equations. The cutting speed was identified as the key parameter in influencing the tool life followed by feed rate and fiber orientation. Machining force variations were constantly monitored during end milling tests, which are mainly attributed to the growth of tool wear and fiber orientation.

INNOVATIVE MANUFACTURING OF CARBON NANOTUBE-LOADED FIBRILLAR POLYMER COMPOSITES

The concept of microfibrillar composite (MFC) has been used to create a new type of polymer composites, in which the reinforcing microfibrils are loaded with carbon nanotubes (CNT). Polyamide 66 (PA66) has been melt blended with polypropylene in a twin screw extruder with and without CNT, and thereafter cold drawn to create a fibrillar state as well as to align the CNT in the PA66 microfibrils. The drawn bristles were compression moulded at 180°C to prepare MFC plates. The scanning electron microscope (SEM) observations indicate near perfect distribution of CNT in the reinforcing PA66 microfibrils. Although the fibrillated PA66 is able to improve the tensile stiffness and strength as expected from the MFC structure, the incorporation of CNT does not exhibit any further enhancing effect. It rather adversely affects the mechanical properties due to poor interface adhesion between the matrix and the reinforcing microfibrils with the presence of CNT, as demonstrated by SEM. However, the resulting highly aligned CNT within the MFC are expected to affect the physical and functional properties of these composites.

Finite Element Simulation on Thermoforming Acrylic Sheets Using Dynamic Explicit Method

After optimising the critical material parameters obtained from hot tensile tests, a dynamic explicit software package, PAM-FORM™, is used to simulate the thermoforming process of polymeric sheet. A hyperelastic constitutive law based on the Mooney-Rivlin model has been successfully adopted to carry out the initial simulation on bubble inflation and to identify the material parameters. It has shown a good agreement of the deformation profile with the experimental results. In this paper, further investigations are concentrated on the thickness distribution analysis and the strain states of the bubble inflation along with a comparison to the results from kinematic Grid Strain Analysis (GSA). The numerical simulation of pressure forming of a cup, whose forming mechanisms have been explained reasonably well with the available Williams’ analytical solutions, is also presented. For a more academic case, the adaptive mesh refinement scheme has been employed in the simulation of thermoforming a complex-shaped rectangular container to well predict the wall thickness distribution. The final simulation results of the deformation at different stages of forming process and the analyses of final part geometry are also presented.

Nanofibrillar Poly(vinylidene fluoride): Preparation and Functional Properties

Poly(vinylidene fluoride) (PVDF) forming β-phase polymorphic modification shows strong ferro- and piezoelectric property as a crucial electroactive polymer and can be obtained by subjecting the highly oriented PVDF fibers to strong electric fields. Two different nanofibrillar materials: PVDF nanofibrillar single polymer composite (NF-SPC) and electrospun PVDF nanofibers were produced for this research. PVDF NF-SPC was prepared by hot compaction of PVDF nanofibrils separated from a PVDF nanofibrillar composite and a high electric field was used to drive out electrospun PVDF fibrils. Polymorphic change and morphology of constituents of the two samples were investigated and measurement of ferro- and piezoelectric behavior was performed after poling treatment. As a result, highly oriented nanofibrils were observed from the two samples and the formation of the β-phase was clearly detected compared to undrawn isotropic PVDF. Higher remnant polarization values and piezoelectric resonance behavior were detected from the samples, in which the β-phase polymorphic modification dominates.

Flammability, thermal and dynamic mechanical properties of bamboo–glass hybrid composites

This study evaluates the influence of hybridization on the flammability, thermal, dynamic mechanical and impact properties of bamboo–glass hybrid polypropylene composites. Flammability tests using cone calorimetry show that the hybrid composites performed better than the glass–polypropylene (GPP) composites, exhibiting a minimum reduction of 19% on the heat release rate (HRR) and smoke release as well as taking longer to ignite. Thermogravimetric analysis (TGA) reveals that the hybrid composites are thermally more stable before starting to degrade at 275°C and fully degraded at 400°C. The dynamic mechanical analysis shows an increase in the storage modulus indicating higher stiffness and lower damping ratio in the case of hybrid composites. The charpy impact strength of the hybrid composites was increased to 1129.2 J m−1 compared to 530.9 J m−1 of bamboo–polypropylene composites. These results indicate that, by replacing several layers of glass with bamboo fabric in GPP composites, a hybrid concept is feasible for developing an excellent and economical lightweight composite.

Natural Fibre-Reinforced Thermoplastics Processed by Rotational Moulding

Rotational moulding or rotomoulding is a manufacturing process best suited for producing one-piece, hollow plastic products. The raw materials can be in powder or liquid form with linear polyethylene of varying densities being dominant worldwide. Due to the modest material properties of polyethylene, reinforcement in various forms have been incorporated within the rotomoulded components to improve the performance of these products. With the abundance and eco-friendliness of natural fibre resources, this study has focused on the use of sisal and woodfibres along with linear medium density polyethylene (LMDPE) powder to produce rotomoulded composite components. Tensile and impact properties of the rotomoulded natural fibre-reinforced composites have been determined as a function of fibre content.

Analysis of the Mechanical Properties of Rice Husk Reinforced Polyethylene Composites Using Experiments with Mixtures

In recent years, the use of agro-wastes, such as rice husk (RH), in the manufacture of thermoplastic composites to replace wood fibres has emerged as a promising field of interest. Linear medium density polyethylene (LMDPE) and ground rice husk (GRH) were used to manufacture composites. The D-optimal design routine in Design Expert software was used to select ten different blends with different percentages of RH, MDPE and compatibiliser, maleated polyethylene (MAPE) along with four replicate blends. RH was varied between 15 to 50 wt%, MAPE between 1 to 6 wt% and MDPE between 44 to 84 wt%. The effects of RH, MDPE and MAPE content on the mechanical properties of the manufactured composites were examined. The results show that tensile and flexural properties of the composites were improved, whereas, Charpy impact strength was decreased with increasing RH loading. The effect of MAPE on tensile strength and Charpy impact strength was significant, but its effect was negligible on tensile modulus, flexural strength and flexural modulus of the composites.

Multi-Functional Properties of Wool Fibre Composites

Composites sheets based on short wool fibres and polypropylene were fabricated by extrusion process. A three-factor two-level experimental design using Taguchi method was applied in manufacturing the composites to explore the contribution of each parameter on mechanical properties. Fire retardant behaviour of the composites with different fibre weight ratios was investigated by horizontal burning test and cone calorimetric analysis without the addition of any fire retardant agent. Reduction of burning rate with increase in the wool fibre content was observed and suitable formulation of the composites was selected for evaluation of mechanical properties.