Volume 36, Issue 9

Graphene oxide (GO) was prepared by the Hummers method and was grafted by an amino-terminated vinyl polydimethylsiloxane (AP). The AP-modified GO (GO-AP) was incorporated in poly(methylmethacrylate) (PMMA) to prepare nanocomposites. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis were used to characterize the particles. The mechanical properties, thermal stability, thermal conductivity, and dispersing status of the PMMA-based nanocomposites were also investigated. The results indicated that AP was grafted on the surface of GO via the amidation reaction, and the quantity of the grafted AP was approximately 20 wt% that of GO-AP. With the addition of GO-AP, the three-point bending strength of GO-AP/PMMA increased to approximately 58 MPa, and the dispersion of the particles was also enhanced. GO wrapped by AP could not form thermal conducting networks at the percolation thresholds. The increasing amount of AP prevented the formation of thermal conduction network and decreased the thermal conductivity of the composites. The thermal stability of the composites was affected by three main reasons, and the total effect of the three reasons on thermal stability illustrated a negative trend.

Exfoliated graphite nanoplatelet (GNP) polypropylene (PP)/kenaf fiber (KF) hybrid nanocomposites (PP/KF/MAPP/GNP collectively presented as PKMG) were developed through melt extrusion using a co-rotating screw speed extruder. The loadings of GNPs in nanocomposites were varied from 1–5 phr and characterized for thermal conductivity, stability and behavior, morphology, and heat deflection temperature (HDT). Results revealed increasing effective thermal conductivity with increasing inclusion of GNP. This behavior was attributed to the formation of thermally conductive, interconnected, sheets of GNP which enhanced heat dissipation. Thermal stability analysis revealed high thermal residue content at 3 phr loading attributed to uniform dispersion of GNP sheets in polymer matrix and the formation of enhanced oxygen-barrier due to effective char formation. Results also revealed enhanced HDT (0.46 MPa/1.8 MPa) with increasing incorporation of GNP ascribed to high modulus and thermal stability of GNP sheets. This implies capability of material to sustain loading at high temperatures without losing its rigidity. Thermal behavior revealed increased crystallization temperature and reduced degree of crystallization with slight increase in melting temperature in the range of 2–5°C. Morphological analysis using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed exfoliated and uniform dispersion of graphene in matrix polymer at 3 phr loading.

Spherical glutaraldehyde cross-linked poly(vinyl alcohol) (PVA) hydrogels (G-PVA) were prepared in three steps: gelatification, cross-linking, and removal of alginate. Gelatification was carried out by dropping a solution of alginate, PVA, and glutaraldehyde into a calcium chloride solution to form calcium alginate. Calcium alginate gels were prepared at 20°C, 40°C, 60°C, and 80°C to study the effect of gelatification temperature on the formation of pores on the surface of G-PVA. The effect of the alginate content was studied. PVA and glutaraldehyde were cross-linked by immersion of the gels in a solution of H 2 SO 4 and Na 2 SO 4 . The effect of sodium alginate and inorganic salts, such as MgSO 4 and K 2 SO 4 , on the formation of pores on the surface of G-PVA was confirmed.

In this study, thermoplastic elastomers based on polypropylene (PP) and ethylene-propylene-diene terpolymer (EPDM) were prepared via direct melt blending in a novel vane extruder. The influence of processing temperature and rotor speed on the degree of cross-linking of the EPDM phase, the tensile properties, the melting behavior and the crystallization morphology of PP/EPDM blends was investigated. It was observed that the volume fraction (V r ) of the vulcanizate arriving swelling equilibrium reached the maximum value when the processing temperature was 190°C. The tensile properties showed better performance at 195°C, at which the PP/EPDM blend obtained good dispersive mixing performance. Moreover, the V r of the vulcanizate arriving swelling equilibrium reached the maximum value when the rotor speed was 60 rpm, at which the dispersive mixing performance and tensile properties of the PP/EPDM blend were better.

The effects of processing conditions for peelable heat sealing of multilayered polyethylene (PE) films on heat sealing behavior and heat seal strength were investigated. Two sets of seal bars, knurled shape and flat shape, were used for heat sealing. After the heat sealing, the sealed portion was cooled using a set of cooling bars. Heat sealing temperature was adjusted to yield the heat seal strength of 4.0 N/15 mm, 6.0 N/15 mm and 8.0 N/15 mm at the heat sealing pressure of 0.4 MPa for each set of heat sealing bars. The heat seal strength increased with the increase of heat sealing pressure for the knurled shape bars, while it was less affected by heat sealing pressure for the flat shape bars. In situ measurements of the sealing bar clearance and interface temperature revealed that the reduction speed of clearance was significantly affected by the pressure for knurled shape bars, while it was almost independent of pressure for flat shape bars. Even though the temperatures set for the similar heat seal strength were different between knurled and flat shape bars, the maximum temperatures at the interface were almost identical. The effect of the shape of seal bars on heat seal strength became less significant after the sterilization process.

The effect of adding poly(L-lactic acid) (PLLA) with and without a pro-oxidant additive cobalt stearate (CoSt) and compatibilizer maleic anhydride grafted polyethylene (MA- g -PE) on the thermal degradation and stability of high-density polyethylene (HDPE) films was analyzed using thermogravimetric analysis (TGA). The kinetic parameters [i.e. activation energy ( E a ), order of reaction ( n ), and frequency factor ln( A )] of the samples were studied over a temperature range of 25°C–600°C at four heating rates (i.e. 5, 10, 15, and 20°C/min) through model-free techniques (e.g. Friedman, second Kissinger, and Flynn-Wall-Ozawa) and model-fitting techniques (e.g. Freeman-Carroll and Kim-Park). The value of E a for neat HDPE was found to be much higher than PLLA; for the HDPE/PLLA blend, it was nearer to that of HDPE. An increase in the activation energy of 80/20 (HDPE/PLLA) blend was noticed by the addition of MA- g -PE. The TGA data and degradation kinetics were also used to predict the lifetime of the film samples. The lifetime of HDPE was found to decrease with the increase in the concentration of CoSt, thereby revealing its pro-oxidative ability. Minimum lifetime was noted for the HDPE/PLLA (80/20) sample blended with CoSt, which increased slightly in the presence of MA- g -PE. Studies indicated that the thermal degradation behavior and lifetime of the investigated film samples depends not only on the fractions of their constituents but also on the heating rates and calculation technique.

Biomaterials used as loading-bearing orthopedic implants usually require various excellent properties such as mechanical, bioactive and bio-tribological performances. Moreover, all of the orthopedic applications feature stress concentrations (notch sensitivity) in their design. In the present work, hydroxyapatite-reinforced polyetheretherketone functional gradient biocomposites (HA/PEEK FGBm) were successfully prepared by the layer stacking method combined with hot pressing molding technology. The effects of notch geometry on the stress-strain behavior of HA/PEEK FGBm were evaluated. The fracture morphology was investigated by scanning electron microscopy (SEM). The study of the stress-strain behavior indicated that the tensile and flexural stresses of HA/PEEK FGBm linearly increased with increasing strain under all the notch sensitivities. The fracture strain of the biocomposites decreased with increasing stress concentration factor and total HA content in the functional biocomposites. Moreover, the tensile and flexural strengths of HA/PEEK FGBm were lower than those of homogeneous HA/PEEK biocomposites. The SEM observation of the fracture micro-morphology showed that the fracture mechanism of HA/PEEK FGBm was gradually controlled by the brittle fracture process. Furthermore, both the tensile and the flexural strengths of HA/PEEK FGBm decreased with the increase in stress concentration factor and total HA content in the biocomposites.

Cellulose derivatives, such as cellulose acetate (CA), are commonly used due to their ease of processing. These polymers present interesting mechanical properties and biodegradability, but low thermal stability under melt processing conditions. Composites of carbon nanotubes (CNTs) and cellulose derivatives are expected to present enhanced properties, depending on the effect of nanotubes on polymer structure and thermal properties. This work aims to investigate the influence of melt mixing on the stability of CA and its CNT composites. Composites with 0 wt%, 0.1 wt% and 0.5 wt% CNTs, as received and functionalized with pyrrolidine groups, were prepared using a batch mixer and an extruder. Chain scission of CA occurred during processing, but the effect was considerably reduced in the presence of CNTs. The incorporation of small amounts of CNTs (with or without functionalization) decreased polymer degradation by thermomechanical effects induced during polymer processing.

A new technique of resin infusion, called the air cushion method (ACM), has been developed to improve infusion time associated with the vacuum assisted resin transfer molding (VARTM) process. The method utilizes an innovative vacuum bag consisting of a bagging film and air cushions. After the preform is sealed by the bagging film and then evacuated, distribution channels are created between air cushions for flow enhancement during infusion. Once the required volume of resin is infused, the bonding interfaces between the air cushion and the bagging film are punctured and distribution channels collapse. The ambient pressure is applied on the bagging film that entirely compacts the preform. This paper investigates the infusion process in ACM using flow visualization experiments. An approximate estimation of the equivalent permeability of the bulk distribution channel is provided. Finally, an assessment of the properties of the ACM part is performed in comparison with VARTM part.

3D molded interconnect device (3D-MID) is a kind of injection-molded thermoplastic part with integrated electronic circuit traces. Currently, it is a hotspot of the electronic and telecommunication equipment industry. Laser direct structuring (LDS) is the main approach to fabricate 3D-MID. Laser scans and activates the surface of thermoplastic parts. After plating, the activated area is coated with copper. In this study, a model was built to describe the mechanisms of interaction between a substrate and laser. The nanosecond laser was applied in the LDS process to manufacture 3D circuit on 3D-MID. With the aid of variable laser pulse width, the model was confirmed by a series of experiments including investigations of roughness, surface structure and energy spectrum. Finally, critical factors affecting the LDS process were found out. They are effective guides for many LDS applications.