Volume 23, Issue 2

We have used plasma assisted surface fluorination of polyethylene terephthalate (PET) fabrics to increase the water repellency of the fabrics. Treatment at different operating conditions for the radio-frequency inductively coupled in a SF 6 atmosphere resulted in improved hydrophobicity. The water repellency of treated fabrics was characterized by water contact angle and absorption time measurement. The measured contact angle of optimum-treated fabrics was 140 degrees, and the absorption time was 210 min. The morphology changes in the surface of PET were obtained by scanning electron microscopy and atomic force microscopy. The rms surface roughness of PET was increased from 28 nm to 45 nm after plasma treatment. The changes in chemical composition were observed in X-ray photoelectron spectra (XPS) analysis. We found that the F/C atom ratios obtaining by XPS analysis on PET were correlated to the pressure, the RF power, and the treatment time. An increase in the F/C atom ratios seems to contribute to the absorption time.

Epoxidized natural rubber with 30 mol.% of epoxide (ENR-30) was blended with medium nitrile rubber (NBR) at the blend weight ratios of 30/70 and 70/30. Blend compounds were prepared via simple mixing and masterbatch techniques using TBBS as an accelerator. The masterbatches of ENR-30 initially consisted of higher accelerator concentrations compared with those of NBR, in order to compensate an effect of accelerator partition towards NBR phase. The initial accelerator concentration ratios in ENR-30 and NBR masterbatches before blending were at 50/50, 60/40, 70/30 and 80/20, respectively. The blend vulcanizates prepared by masterbatch mixing showed a significant improvement in tensile properties in comparison with those prepared by simple blend, and the initial accelerator concentration ratio in ENR-30/NBR masterbatches at 70/30 gave the highest ultimate tensile properties. The improvement in tensile properties was clearly observed for all the blends vulcanized with conventional, semi-EV and EV sulfur-vulcanization systems. The increase of tensile properties does suggest a better curative distribution, and hence a better crosslink distribution.

The high oxygen permeability film, so-called breathable film, can be produced via reactive blending and processing of linear-low density polyethylene, natural rubber, and epoxidized natural rubber with a small content of maleic anhydride as a reactive coagent. The foam-like structure of the produced breathable film was created by the reaction between the functional groups during the extrusion. Oxygen permeability of the blended films can be controlled by the blend composition, screw speed, and draw ratio during the chill-roll casting step. The blended films exhibit not only the good breathablility but also the outstanding UV screening with a small transparency trade-off. These properties are suitable for the films to be used in agricultural applications to enhance the growing and production of fruit trees, flowers, vegetables, and even grains, especially during the growing stage of plants.

Film blocking typically observed in both mPE and higher modulus mPE/PP blends could be effectively reduced or prevented through the incorporation of only 2 wt.-% of rigid PS or PMMA into the blends. Blocking forces required to separate the two adjacent layers of mPE/[PP/PS] and mPE/[PP/PMMA] films were significantly reduced from 20.9 g for the neat mPE, to 0 g and 10.8 g, respectively. Films containing rigid PS, however, possessed high haze of 32.37 % while a much lower haze of 10.88 % was obtained for films with PMMA. Based on atomic force microscopy (AFM) results, total haze increased systematically with an increase in RMS surface roughness. Nevertheless, there seemed to be a critical surface roughness that could give rise to both low film blocking and low optical haze, as found in the mPE/[PP/PMMA] films. All developed films also had suitable mechanical properties and high oxygen transmission rates, OTR (> 10 000 cm 3 /m 2 day); these high OTR films are desirable for fresh produce packaging. Current findings also demonstrate that controlling film morphologies of these mPE blends with PS and PMMA through mixing and processing principles appears to be a promising route in determining surface roughness and internal structure that have direct influences on film blocking and clarity or haze.

Co/terpolymers of L-lactide (LL), ∊-caprolactone (CL) and glycolide (G) are biodegradable in the human body and, as such, have considerable potential for use in biomedical applications such as absorbable surgical sutures, nerve guides, bone fixation devices and drug delivery systems. This study focuses its attention on their potential as monofilament fibers for absorbable suture applications. Random co/terpolymers with different compositions of LL, CL and G were synthesized via bulk ring-opening polymerization. The polymers obtained were melt spun at slow speeds into ice-cooled water to produce as-spun monofilament fibers with as little molecular orientation and crystallinity as possible. Combinations of off-line hot-drawing and annealing steps under controlled conditions of draw rate, draw ratio, temperature and time were then employed in order to develop the fiber's oriented semi-crystalline morphology. The mechanical properties of the fibers were tested after each processing step and compared. The tensile test results showed that the tensile strength was strongly dependent on the draw ratio. A high draw ratio was obtained by multiple off-line hot-drawings with intermediate annealing. The first hot-drawing step dramatically enhanced the mechanical properties relative to those of the weak, highly extensible as-spun fiber. Subsequent annealing at a suitable temperature and for an appropriate length of time increased fiber flexibility as a result of molecular relaxation. Additional hot-drawing steps, again under precise temperature-time conditions, increased the total draw ratio and further enhanced the fiber's mechanical strength.

The presence of long-chain branching provides advantageous properties to a molten polymer in film production, especially for a fast growing commodity plastic such as polyethylene. Besides the innovation of polymerization, the most attractive method to tailor the molecular structure is peroxide modification via reactive processing which is the post-reactor technique. By this process, it can achieve the enhancement of ability of the melt to be drawn or stretched during the film processing due to branching. However, to avoid the undesired excess of macroscopic molecular network, which may cause defects in the film product, a small quantity of peroxide initiator was used to modify the base resin. The rheological properties, as related to molecular characteristics, were investigated using a capillary rheometer. Rheological analysis of the products modified by different peroxide addition methods was of interest as changes in rheological properties depend markedly on the efficiency of incorporating and mixing the peroxide into the polymer. Process parameters (including mixing temperature, peroxide quantity, and mixing speed), which appear to be responsible for the molecular characteristics alteration, were considered in order to produce materials with preferred rheological properties.

The effect of impregnated carbon dioxide (CO 2 ) and pressure on dynamic viscoelastic responce of a commercial LDPE was investigated by a magnetic driven rotational rheometer equipped with a high-pressure chamber. It was found that i) the mode distribution of the viscoelastic relaxation is not sensitive to CO 2 pressure realizing the superposition among moduli obtained at different pressures, that ii) the horizontal shift factor for the superposition reflecting the monomeric friction exponentially decreases with increase of the pressure, and that iii) the vertical shift factor relating to the entanglement number density is not sensitive to the pressure. From the observation it is suggested that CO 2 and pressure mainly affect the monomeric friction and the effect on the entanglement dilation is not significant. The results are consistent with the dielectric measurement on polyisoprene (Matsumiya et al., Nihon Reoroji Gakkaishi, 35, 155–161, 2007).

Development of bicomponent spunbond nonwoven consisting of ultra-fine splitted polypropylene (PP) and polyethylene (PE) fibers was described. The morphological structures developed in bicomponent spinning of PP/PE fibers with the cross-sectional configuration of “sixteen-segment hollow pie” were investigated in relation to molecular properties as well as the resulting fiber splittability. Structure developed in each component in the melt spinning process was found to depend not only on its molecular properties but also on those of the other component. Results showed that the PP/PE pair exhibiting good splittability possesses high molecular orientation in both components.

Film insert moldings were produced from amorphous and crystalline polymers, i. e. PC + ABS and PET respectively. The vastly different characteristics of these polymers provide an interesting platform to study the mechanisms that are responsible for interfacial bond formation, particularly when these materials were molded at different molding conditions. It was observed that intermolecular diffusion between amorphous polymers takes place at virtually any temperature as long as it is kept above the glass transition temperature of the material, though higher temperatures are favorable to accelerate diffusion. As for crystalline polymers, there is an initial need to create free and mobile molecular chains by heating the materials to its melting temperature before any significant diffusion takes place. Certain criteria have to be met, irrespective of the materials used, before good interfacial bonding is achieved. Firstly, the injection molding parameters should be optimized to ensure intimacy between the surfaces of the film and injected resin. Once this is achieved, interdiffusion of molecules should be promoted to ensure extensive film-substrate molecular entanglements. The state of molecular entanglement should then be retained for a sufficient amount of time as the material solidifies in order to obtain good film-substrate adhesion.

Experiments are conducted to study the solid particle erosion wear behavior of glass reinforced polyester composites with flyash as a filler material. This study makes use of a methodology based on Taguchi's experimental design approach to characterize the erosion response of these composites. The procedure eliminates the need for repeated experiments and thus saves time, materials and cost. It identifies not only the significant control factors but also their interactions influencing the erosion rate predominantly. From the experimental findings an optimal combination of control factors is obtained on the basis of a proposed predictive model. This model is validated by performing a confirmation experiment with an arbitrarily chosen set of factor combination. Finally, optimal factor settings for minimum wear rate under specified experimental conditions have been determined using genetic algorithm.

Commercial blow moulding grade recycled high density polyethylene (r-HDPE) and blow moulding grade virgin HDPE were reactively extruded with various compositions (0.00 to 0.15 %) of different peroxides in a twin screw extruder. The aim was to improve the melt strength properties of a blow moulding grade HDPE homopolymer – a polymer resin comprising a significant part of the post consumer recycled plastic stream in Australia. Melting behaviour and crystallinity were investigated by modulated differential scanning calorimetry (MDSC). Uniaxial melt extensional (UME) measurement of the modified materials was carried out using Göttfert Rheotens melt strength tester to measure melt quality of the material. Melt strength and zero shear viscosity were also measured to assess and correlate changes in melt properties due to peroxide modification. Melt strength and zero shear viscosity of both recycled and virgin material were enhanced with the increase in composition of peroxide. However, addition of peroxide also brought with it flow instabilities like draw resonance and necking, both of which lead to limitations in polymer processing.

The ability to predict segregation of the solid phase in processes such as powder injection molding and injection molding of semi-solid materials is of special interest since such phenomenon affects the final properties and characteristics of the molded parts. In powder injection molding, for example, defects appear very often in the debinding and sintering stages but are caused by filling problems and determined by a non-uniform distribution of the solid particles within the molded part. In this paper we propose a 3D numerical solution algorithm for the simulation of particle migration in dense suspensions. The particle migration is modeled using the diffusion flux model and integrated into the NRC's 3D injection molding software. The solution algorithm is validated by solving flow problems for which experimental and numerical data are available: circular Couette flow, piston driven flow and sudden contraction-expansion flow. Since it is observed that the piston movement in the sleeve can induce particle migration even before the material enters the cavity, an ALE (Arbitrary Lagrangian-Eulerian) formulation is also developed to include the piston movement in molding simulations. The ALE formulation is first compared with an Eulerian solution for the case of the piston driven flow problem. Then, the approach is applied to injection molding problems and the segregation inside the molded parts is studied.

An experimental study was carried out to investigate the pickout of scaled-up gravure cells. The pickout of a gravure cell is defined as the fractional volume of the coating solution transferred from the cell to the moving roller. Gravure cells of different sizes and combinations were examined. Dilute poly(vinyl) alcohol solutions was used as test fluids. It was found that the stability of the liquid bridge that connects the moving roller and the gravure cell is the most critical factor to determine the pickout. The most stable condition that yields the maximum pickout is that the moving roller just touches the gravure cell and the coating gap is zero. Either a positive or a negative coating gap will decrease the pickout. The pickout for a small gravure cell is lower than a larger one because the liquid bridge is less stable. The experiment on different cell combinations reveals that if the number of gravure cells in the coating direction is increased, the average pickout per cell will drop. The pickout decreases as the capillary number increases. A universal correlation was found between the modified pickout and the capillary number. This modified pickout is the product of the pickout and a shift factor which involves all the geometric parameters in gravure cells.

Fly ash (FA) is utilized as a filler to reinforce reclaimed rubber powder (RP) composites by using a coupling agent. FA content is varied between 10 and 35 phr. The optimal formulation of FA/RP composites and experimental process variables were determined by measuring mechanical and thermal properties. A study of compatibility and cross-linking by SEM and IR shows that FA/RP composites offer superior mechanical and thermal properties when the accelerator (M) and stearic acid (SA) are added first, then mixed with sulfur and dicumyl peroxide (DCP), and finally r-Aminopropyltriethoxysilane (KH-550). The mass ratio of the FA/RP composites is 25/100, and the cure condition is 145°C for 40 min under 9 MPa. The results indicate that FA is an excellent filler and can be used as a silica replacement for reclaimed rubber powder composites.

The purpose of this study is to determine to what extent CO 2 can be used as a processing aid to melt process polyethylenes of higher molecular weight than can be typically melt processed. To assess the ability to melt process high molecular weight polyethylenes with CO 2 , the viscosity of a 460 000 g/mol high density polyethylene (HDPE) plasticized with various amounts of absorbed CO 2 in an extrusion process was determined using a slit die rheometer that was attached to the end of the extruder. A relationship was developed to determine the maximum molecular weight polyethylene that could be processed at a given viscosity reduction due to absorbed CO 2 . This relationship was tested by using CO 2 to process a blend of 40 weight percent ultra-high molecular weight polyethylene (UHMWPE) and the 460 000 g/mol HDPE which lead to an equivalent molecular weight of 720 000 g/mol. The viscosity of the blend with 12 weight percent CO 2 was reduced to that of the pure 460 000 g/mol HDPE as predicted by the relationship. Preliminary studies using a pressurized chamber attached to the exit of the die allowed one to assess the conditions under which suppression of foaming within fibers or other extruded forms is possible.