SPE Library

Devolatilization is a key-step in polymer processing. Low-molecular-weight components are removed from a polymeric system. On of the most used equipment for devolatilization is the extruder. The mass transfer rate inside the devolatilization section of an extruder depends on the flow regime. A double-screw extruder with a transparent barrel is used for the experimental investigations to correlate the mass transfer with the flow regime. At the entrance section of the devolatilization section the polymer starts to foam. Two-phase bubbly flow exists. There the mass transfer is highest. The intensity of the foam expansion depends mainly on the rotational speed of the screws and the inlet concentration. After the foam has collapsed it may foam again under the vacuum vent. Down stream behind the vent two-phase stratified flow exists. There the mass transfer is low. The flow field along the screws is filmed with a digital video camera.

Polypropylene grafted with maleic anhydride (PPgMA) was modified using different diamines during the melt. Two-layered films were prepared using polycarbonate (PC) film and PPgMA modified with diamines (PPgNH2). Adhesion strength was measured using T-peel Test. FTIR data showed that the addition of the diamine caused an imide linkage, which is performed between the amine primary group of the diamine and the maleic anhydride functionality of the PPgMA. The adhesion between layers of PC y PPgNH2 was found to be improved using PPgNH2. No adhesion was found between layers of PPgMA and PC, but the adhesion was improved when using PPgNH2 instead of PPgMA.

It is common that a highly filled master batch (MB) contains a low molecular weight (LMw) lubricant as a filler dispersion agent and compounding processing aid. Sometimes, the presence of such a lubricant in the MB creates a die build-up problem in the extrusion process of a let-down formulation. Several MBs with a laboratory Banbury mixer were produced to investigate the effect of the amount of aluminum stearate (as a lubricant) on dispersion and die build-up. When the MB containing the stearate below the critical amount is used, die build-up decreases and filler dispersion improves with increased amounts of stearate. At the critical amount of the stearate, the MB shows good dispersion as well as minimum build-up. Above the critical amount, dispersion is still good. But, build-up increases with further increase in the amount of stearate added up to 3.0%. This observation results from the different mechanisms of the die build-up, which depends on whether the stearate level is below or above the critical amount. We confirmed such a mechanism in the commercial extrusion process of the MBs. This observation leads to the conclusion that in the use of the stearate (as a dispersion agent) for highly filled MB, the amount of the stearate need to be optimized to minimize a die build-up of the MB with good filler dispersion.

This study extends our earlier work on the fundamental aspects of modeling on foaming aging and dimensional stability. The thickness change of extruded polyolefin foam to the blowing agent and air counter diffusion during the post-extrusion aging process is modeled. The blowing agent and air counter diffusion equations are coupled with more complicated Maxwell-Voigt four-parameter viscoelastic equations to model the foam dimensional change and recovery processes. The effects of blending ethylene-styrene interpolymer resin and adding aging modifier are investigated, respectively and altogether. The mathematical model is also compared with experimental data.

The vacuum assisted resin transfer molding (VARTM) process is a cost effective, innovative method that is being considered for manufacture of large aircraft-quality components where high mechanical properties and dimensional tolerance are essential. In the present work, carbon fiber SAERTEX fabric/SI-ZG-5A epoxy resin C-shaped laminates were manufactured by VARTM using different cure cycles followed by the same post-cure cycle. The final part thickness was uniform except at the corner were thinning was observed. The cure cycle selected is shown to significantly affect the part spring-in and a long cycle at 66°C followed by a 178°C post-cure produced a part with negligible spring-in.

New technological developments in micro-fabrication have created the need to assemble thermoplastics components with narrow weld joints (~100 ?m wide). This paper reviews the use of fiber coupled laser diodes in conjunction with special lenses to produce spot sizes between 25 and 50 ?m in diameter. The effects of travel speed, power density and pressure on weld line width, consistency and strength were evaluated. It was found that process parameters are extremely critical in producing consistent welds. In addition, new testing techniques need to be developed to allow quantitative measurements of weld strength due to relatively small weld area.

This paper presents a method of creating a rapid tool for injection moulding, which can produce components of higher accuracy and better surface finish. Main investigation focuses on the rapid tooling process of a complex part using high speed machining and Electro Discharge Machining (EDM) to produce an injection mould of higher accuracy and surface finish than that achieved by a rapid prototyping based tooling process. Results demonstrate how short-run injection moulds with a higher accuracy could be made in a much faster way using high speed machining and EDM with a lead-time that can match any other methods of rapid tooling process.

This review paper presents certain fresh viewpoints about the already-known process-independent and intrinsic differences in the mechanical design of plastic parts, as also its complexities. This paper is motivated by the fact the mechanical design education in the schools begins from mechanics of materials - predominantly of metals - and that plastics part design education begins from specific plastics processes. The predominant process-orientation is marked by the fact that the presence of text book titles such as “Design for Injection Molding”, or “Design for Rotational Molding” stand in contrast with the absence of titles such as “Design for Turning on Lathes”, “Part Design for Milling and Grinding”, or “Part Design for Five Axes Milling”.Furthermore, it is noted that the advent of CAD/CAE has changed but only the management of the design and development, however, the intrinsic differences remain.It is emphasized that the points discussed herein are well-known, however a fresh viewpoint is presented for the student audience.

Significant developments in finite element modelling of the blow moulding process have been observed in the recent years. The large deformations occuring during parison formation, clamping and inflation have traditionally been modelled using membrane or shell type elements. In this paper, a 3D solid finite element approach for improving the part wall thickness predictions is proposed. A 27-node brick element with incompressibility constraint is presented for modelling large viscoelastic deformations of the parison in the consecutive stages of the process. Part wall thickness predictions using 3D simulations are compared to experimental measurements on two different blow moulding cases. The results are also compared to predictions from the membrane formulation.

Ethylene/1-octene resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. Comparison of the dynamic mechanical (tensile) and rheological properties of these blends shows that increasing the fraction of copolymer in the reactor blend results in a decrease in its stiffness. However, the energy dampening properties of these blends benefit from the presence of the copolymer. It was confirmed that melt flow properties of polymers depend on their molecular weight distribution.

Pressure transients in a capillary rheometer can take hours to reach steady state during low shear rate measurements, causing problems with material degradation during the test. Instead of running the piston at constant speed and waiting for equilibrium, it is possible to use dynamic speed control of the piston to reach the steady state pressure more quickly.Models from literature suggest that the long pressure transients at low shear rates are due to changes in the material density as a function of pressure. These models are used to determine an optimum velocity profile for the capillary piston, reducing measuring times to a fraction of previous times and using less material per test point.

The dynamic mechanical properties of single wall nanotube (SWNT) reinforced polymer composites were studied. This paper analyzes preliminary results between the theoretical and experimental effect of SWNT concentration on anelasticity versus nanotube concentration. The theoretical model assumes that the assembly is a standard linear solid (SLS). The following assumptions were made: 1) the filler material is purely elastic, 2) the only time-deformation is that of the polymer matrix, and 3) the SLS unrelaxed elastic modulus varies linearly with the relative concentration of the filler material. The results indicated that the preliminary studies using the SLS model showed a good approximation to the experimental results within the chosen region.

Mass Transfer between a slender bubble and a non-Newtonian liquid in a simple extensional and creeping flow has been theoretically studied. Exact shapes of slender bubbles in power-law liquids are presented, along with analytical approximations. Steady-state mass transfer is studied assuming the thin concentration boundary layer approximation. The results indicate that the total mass transfer increases with n, the power-law parameter, due to larger surface areas in dilatant liquids compared to pseudoplastic liquids for a similar imposed flow. The relevance of this work to the processes of polymer melt devolatilization and the production of polymer foams is discussed.

The goal of the study has been to identify factors influencing the creation of the Economic Value Added (EVA) of companies in the plastics processing industry. EVA as an indicator of new created value for the owners of the company is an important criterion of success of the company‘s activities. The sources of the creation of EVA are being identified by comparing several plastics processing companies including some in different geographical regions. Some differences in the EVA in the investigated regions have been correlated to technological level, creativity of management and financial ratios. Data for the analysis were obtained mainly from companies´ annual reports.

This paper describes the effect of individual additives that are present in masterbatch formulations, and the role they play in modifying physical properties and processability of blends based on RPET. Additives such as titanium dioxide, carbon black, linear low-density polyethylene and polyethylene wax are often incorporated in masterbatch compositions. The blends based on these additives have been analysed for shifts in thermal transition points, levels of crystallinity and physical properties such as tensile and impact strength. The results show that at the addition rates used, some additives had significant effects on processability and crystallinity, negligible effects on physical properties and antagonistic effects were noted when additives were combined.

Film toughness of certain ethylene – alpha olefin copolymers of high impact strength, shows significant aging effects, decreasing with time. In this work we studied the time and temperature dependence of film aging of several copolymers of varying molecular structure. Film aging appears to be associated with the presence of highly branched polymer chains (>30 branches per 1000 carbon atoms). It is speculated that the thermally activated rearrangement of such branched species, over time and under film storage conditions, leads to film aging. Higher film storage temperatures lead to faster aging. It is possible to employ an “accelerated aging” testing protocol, so as to obtain longer-term aged data from a short-term test, which would be useful in an industrial production setting.

The processability of the polymer in capillary extrusion is closely related to the interface between the polymer melts and die wall, and wall surface energy affects the flow of polymer melts in extrusion dies. In this paper, when used Boron Nitride (BN) with low surface energy as the processing aid, we studied about changes of the rheological behavior and processability of metallocene polyethylene (m-LDPE). It also studied about the effect of the hot-pressed BN die on the instability of capillary flow. The equipment used includes a capillary rheometer with two kinds of dies, namely the tungsten carbide and hot-pressed BN dies. The rheological properties of resins with and without BN particles were analyzed by parallel-plate and capillary rheometers. Two types of BN powders with a different the agglomerated particle size and distribution, are tested at various contents. It was found that the BN powder has an influence on the processability of the polymer, depending on the BN content and particle size.Lastly, it must be underlined that it is possible to significantly delay or eliminate the melt fracture, by considering the polymer flow through the hot pressed BN die instead of the tungsten carbide die.

This study demonstrates how the impact performance of a rigid polyvinyl chloride (PVC) compound can be affected by the particle size of the calcium carbonate filler and its loading level. The test compounds contain 0 to 8phr of acrylic impact modifier and fillers ranging in size from 3 to 0.07 microns. By taking all three variables into consideration one can, not only optimize a compound's performance, but also lower its cost. Notched Izod and falling weight impact data will be reviewed. Flexural modulus and low temperature impact data are also included.

We report results from tensile creep tests performed on an epoxy resin in the presence of carbon dioxide pressure (Pco2) at a constant temperature below the glass transition temperature Tg. Time - Pco2 superposition was applied to the data to account for the plasticization effect due to the interaction between the carbon dioxide molecules and the polymer. In addition, physical aging of the epoxy films was investigated using sequential creep tests after carbon dioxide pressure down-jumps at constant temperature and also after temperature down-jumps at ambient carbon dioxide pressure. The isothermal pressure down-jump experiments showed physical aging responses similar to the isobaric temperature down-jump experiments. However, the aging rate for the CO2–jump was lower than that for the T-jump.

A thermal treatment of Successive Self-Nucleation and Annealing (SSA) of LDPE, LLDPE, PP, PP grafted with diethyl maleate and PP grafted with maleic anhydride were made. The study of these materials was combined using capillary rheometry, DSC measurements, FTIR and Low-Frequency Raman-Active Longitudinal Acoustical Mode (LAM). The results indicated that the grafting process mechanism in a co-rotating twin-screw extruder and their effects on the polyethylenes structures occur through secondary carbons. The SSA technique is a useful tool for the characterization of grafted PEs. However, more work is needed for the grafted MA polypropylenes.