Volume 25, Issue 1

A series of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS)/layered silicate nancomposites were prepared by simple melt extrusion of PLA/PBS/Cloisite 30BX (organically modified MMT) clay. Extruded and compression moulded samples containing 1, 3, 5, 7 and 10 wt.% of clay having 80 and 20 wt.% of PLA and PBS respectively, were prepared to investigate morphological, thermal, mechanical and gas barrier properties of these biodegradable nanocomposites. Wide angle X-ray diffraction (WAXD) was used to assess the periodic distance of the clay layers. WAXD indicated an exfoliated structure for nanocomposites containing 1 and 3 wt.% of C30BX, while, dominantly intercalated structures were noticed for nanocomposites having 5, 7 and 10 wt.% of C30BX. Transmission Electron Microscopy (TEM) images confirmed mixed morphology of intercalated and exfoliated structure even for nanocomposites having 1 and 3 wt.% of C30BX, while some clusters or agglomerated tactoids were detected for higher clay containing (>3 wt.%) nanocomposites. Thermo gravimetric analysis (TGA) revealed the thermal stabilities of polymer blend and their nancomposites. Nanocomposite with 3 wt.% C30BX clay showed enhanced thermal stability compared to other nanocomposites. The effect on the crystallinity, investigated by Modulated Differential Scanning Calorimetry (MDSC) showed slight improvement for nanocomposites having 1, 3, 7 and 10 wt.% of C30BX studied. However, nanocomposites having 5 wt.% of clay content showed higher crystallinity compared to the rest of the nanocomposites. Mechanical properties (tensile strength, % elongation at break and Young's modulus) were measured by Instron Universal Testing Machine. Tensile strength and Young's modulus initially increased for nanocomposites of up to 3 wt.% of clay but then decreased with the introduction of more clay. Oxygen permeabilities of the nanocomposites were also measured. Barrier properties were improved by approximately 26% with the increase of clay content in these nanocomposites.

Urea is a low cost material with thermal and mechanical properties suitable for use in investment casting pattern molding compounds. Conventional compounds are made by a “cooking” process wherein the urea is added to and dissolved in an aqueous solution of a water soluble polymer followed by evaporation of the water. Here we describe novel formulations based on either polyvinyl alcohol (PVOH) plasticized by glycerol or ethylene vinyl acetate (EVA) resins together with wax that can be prepared by a facile twin-screw compounding process. The thermo-mechanical properties of these compounds were characterized using differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), dynamic mechanical analysis (DMA) and three bend point tests. The PVOH-based molding compounds featured better mechanical properties than those based on EVA. Increasing the polymer content produced weaker but tougher molding compounds. Increasing wax content improved stiffness but resulted in a loss of toughness. The TG results showed that both compounds decomposed readily at elevated temperatures and left less than 3 wt.% ash at 800°C.

This paper describes the processing of a class of hybrid composites prepared by filling of SiC particulates in glass fiber reinforced epoxy resin. Experiments are conducted to study the solid particle erosion response of these composites. A theoretical model for the wear rate of the composites during solid particle impact erosion is proposed for predictive purpose. The validity of the theoretical model is assessed with experimental results and the influence of control factors like impingement angle, impact velocity, erodent temperature, erodent size, stand-off distance and filler content etc. on wear rate is studied. For this purpose a novel technique like Taguchi experimental design is employed. It is observed that the erodent temperature, filler content, impact velocity, impingement angle are the most significant factors effecting the erosion rate. The peak erosion rate is found to be occurring at an impingement angle of 75°. The morphology of eroded surfaces is examined by using scanning electron microscopy (SEM) and possible erosion mechanisms are discussed.

Manufacturing of blend man-made fibers especially from polyolefins due to their new and expanded applications has attracted the researchers and technologists' attention. In this study, PP/LDPE blend filament yarn samples with various ratios of 100/0, 99/1, 97/3, 95/5, 93/7, 90/10 were melt spun and then drawn under industrial conditions. According to the results of the melt spinning process, convenient spinnability comparing to pure PP for various polyblend samples up to 10 wt.% of LDPE was observed. Results of microstructure measurements in both group i.e. as-spun and drawn samples showed that the presence of LDPE in blend samples did not deteriorate the density and crystallinity of PP. However, increasing the fraction of LDPE in blend gave rise to noticeable increase in the shrinkage values of drawn samples in comparing to pure PP. Although the tenacity of as-spun and drawn yarns displayed a downward trend by increasing the LDPE in blend, the obtained values for tenacity are still at an acceptable level for further processing or textile applications.

The post-molding warping of injection molded parts is strongly influenced by thermal expansion history. We show that a thermal expansion hysteresis loop occurs, so that heating and cooling curves can sometimes be different, due to microstructural changes. Following an extensive investigation of thermal expansion for a polypropylene, we propose a model to predict the specific volume change during post thermal treatments. The model predictions are in good agreement with the experimental measurements.

This paper describes how to use the semi-empirical thermal expansion model, proposed in Part 1 of this paper (Fan et al., 2010), to simulate the post-molding warping of injection molded parts during the post thermal treatment. The post-molding warping of a viscoelastic ribbed plate and a fibre reinforced ribbed plate are simulated using a finite element method. The results of simulations showed that the post-molding warping due to the thermal treatment for viscoelastic ribbed plate is much larger than the de-mold warpage, in contrast to results for fibre reinforced ribbed plates.

There is considerable experimental evidence that the classical no-slip boundary condition of fluid mechanics is not always a valid assumption for the flow of high molecular weight molten polymers. In fact, molten polymers slip at solid surfaces when the wall shear stress exceeds a critical value. Moreover, there exists a second critical wall shear stress value at which a transition from a weak to a strong slip takes place. The later corresponds to the case of an almost plug flow and it is accompanied by pressure oscillations in the case of capillary flow generated by a constant-speed piston-driven capillary rheometer. The two modes of slip (weak and strong) are due to flow-induced chain detachment/desorption directly from the polymer/wall interface and to chain disentanglement of the polymer chains in the bulk from a monolayer of polymer chains adsorbed at the interface. In this work, the two physical mechanisms of slip are discussed and validated on the basis of suitably analyzed experimental data. Based on these two modes of slip, the slip phenomena observed during the capillary flow of polymers (mainly polyethylenes) are explained including the absence of pressure oscillations in the capillary flow of branched polyethylenes.

This article presents a simulation study of the injection molding of a macroscopic part with microfeatures; an optical grating with amplitude 0.6 μm and period 3 μm. The aim of the simulations is to develop a procedure capable of predicting the replication of optical gratings based on the injection molding processing parameters. Three coupled simulations are performed. 1.) A macroscopic simulation of the flow in the part without microfeatures. 2.) A microscale flow simulation in a domain around a single microfeature using the pressure from the macroscopic simulation as input. 3.) A thermal simulation of the mold wall coupled to the microscale simulation. In the simulations the polymer melt is treated as a generalized Newtonian fluid. Shear viscosity and thermal properties were characterized as part of the study. Other physical effects such as wall adhesion and elasticity are discussed, but not included in the present model. The simulation results agree well with the experimental replication data, and correctly describe how small changes in the mold temperature can lead to large changes in the replication.