SPE Library

Mixing is a critical function in most extrusion operations. One of the most difficult mixing tasks is backmixing. An extrusion operation where good backmixing is very important is when a low percentage color concentrate, CC, is added to a virgin polymer. In this case, the initial distance between the CC pellets may be 100 mm or greater. If the final striation thickness needs to be reduced to the micron level, the reduction of the striation thickness needs to be at least five orders of magnitude - this is quite a tough task! This paper will analyze how the velocity profiles, axial mixing, and residence time distribution are related. It will be shown why simple conveying screws have poor axial mixing capability. New mixer geometries that are specifically designed to improve backmixing will be discussed. Results from extrusion experiments will be presented.

The screw of the plasticating unit of an injection molding machine (IMM) typically consists of a single stage, single flighted conveying screw with a non-return valve at the end. Mixing sections are usually not incorporated into the screw design. One reason for this is the fact that most plasticating units a relatively short; the typical length-to-diameter ratio is 20:1 in IMMs. This does not leave much space to incorporate a mixing element. Another reason may be the mistaken believe that mixing is not very important in the injection molding process. A convenient method to improve the mixing capability of the plasticating unit of an IMM is to design the non-return valve (NRV) such that it has mixing capability. Such a dual-purpose NRV allows an increase in mixing capability without affecting the melting and conveying capability of the plasticating unit. This paper will describe a NRV mixer based on the CRD mixing technology developed for single screw extruders.

UV-B portion of solar radiation adversely affects the physical, chemical, and mechanical properties of exposed plastics and thus their lifetimes are reduced. Mostly polymers used in outdoor applications have UV-stabilizers incorporated in their formulations. The crucial role of temperature on the weathering of polyethylene (PE) was studied. In this paper, polyethylene film samples were exposed to the outdoor weather of Dhahran, Saudi Arabia as well as in low temperature set up maintained at 15°C at all times. The combined effect of high temperature and UV-B radiation on the polyethylene film sample was evaluated in terms of drop in tensile properties and increase in carbonyl absorbance. Higher UV-B together with high temperatures encountered in this region cause faster degradation of polymeric materials.

The paper illustrates the results of the first phase of a project investigating the area of major interest for sequentially operated valve gates, followed by the developments of a procedure for their implementation in family molds applied to very dissimilar parts. The activity covered the use of computer simulation to determine location, dimension and actuation time of gates during filling and holding phases. Some results are checked by molding on a specially designed mold. The methodology can exploit the potential of this technology to reduce tooling and molding costs with the added benefit of the best color matches of molded parts.

Prior work by Michigan Technological University showed that for nylon 6,6 based resin there was a synergistic effect on electrical conductivity due to the combination of electrically conductive carbon black, milled synthetic graphite, and PAN-based carbon fiber. The purpose of this present study was to conduct an experimental design to quantify the effects of these three different fillers (carbon black, synthetic graphite, and carbon fiber) on the electrical properties of the resulting nylon 6,6 composites.

The rate of silica particles agglomerate breakdown in an laboratory internal mixer were measured and compared with carbon black, calcite, talc and zinc oxide particles. Silica agglomerates exhibited the highest agglomerate size. The rheological behavior of each compound was investigated. Small silica particle filled system exhibited highest viscosity level.

Rotational molders are lightweighting their parts by adding chemical blowing agents to their polymers. However, they are finding to their dismay that it is just as difficult to produce controlled voids as it is to eliminate voids. This paper highlights the mechanism of cell formation as an aid to those struggling with foam production.

Fractography is critical to failure analysis of metals and plastics. Fractography of plastics is a relatively new field with many similarities to metals. Utilizing case histories, various aspects of failure analysis and fractography are compared and contrasted. Common failure modes include ductile overload, brittle fracture, impact and fatigue. Analogies can also be drawn between stress corrosion cracking (SCC)/stress cracking, corrosion/ chemical aging, dealloying/scission, residual stress/frozen-in stress, and welds/knit lines. Stress raisers, microstructure, material defects, and thermo-mechanical history play important roles in both cases. Key fractographic features for metals and plastics are described.

This study examines the effects of particle size on the consolidation quality and mechanical performance of carbon fiber-reinforced composites fabricated from dry powder coated carbon fiber tow (towpreg). Poly(ether ether ketone) (PEEK) powder was sieved to produce three different particle size distributions; a minimal polymer powder deposition system was used to coat carbon fiber tow with these distributions and unsieved polymer. Unidirectional composite panels were manufactured from these four batches of towpreg and APC-2 (PEEK / AS4) prepreg using an identical processing schedule. Poor consolidation quality of some panels limited conclusions. However, these results did bring forward several questions concerning the effects of powder particle size distribution on the processing of composites from PEEK/G30-500 towpreg that may be addressed in future studies.

The MuCell® molding technology is a proprietary manufacturing process for producing microcellular foamed plastics. The microcellular foam process uses supercritical fluids (SCFs) of atmospheric gases to create evenly distributed and uniformly sized microscopic cells throughout a polymer. Suitable for injection molding, this breakthrough foam process enhances product design, improves processing efficiency, and reduces product costs. This foam process does not require chemical blowing agents (CBAs), hydrocarbon-based physical blowing agents, nucleating agents, or reactive components. The microcellular foam molding technology permits molders to reduce raw material consumption while producing strong, lightweight products, extending considerably the applications of foamed polymers. This paper describes those benefits, shows the effect of processing conditions on cellular structure and reviews some successful applications of the technology.

In this work, optimization strategies that employ model-based technologies are developed for minimising the overall weight and improving thickness distribution of an extruded blow moulded part. The part studied is a plastic dumbbell for the recreational sector. Process simulations and preliminary experimental trials are simultaneously performed to assist in the development of the part. Once the numerical modelling methodology is functional, one can perform a process optimization based on a desired objective function, such as uniform part thickness distribution and/or minimal part weight. The optimization is performed in two sequential steps (weight optimization followed by thickness optimization) by the systematic manipulation of the operating conditions, such as the parison dimensions. Furthermore, a commercial procedure modelling technology (i.e. FirstSTEP™) is employed for demonstrating the reduction in the part development time with the new model-based approach.

The electrical resistivity and electrostatic charge dissipation characteristics of carbon black (CB) filled low-density polyethylene (LDPE) thermoplastic composites processed by three-dimensional chaotic mixing were investigated. These properties are reported as a function of carbon black concentration and are related to novel microstructures that have been shown to reduce percolation thresholds. Microscopic analysis of emerging structures is correlated to electrical properties of the composite. Electrical conductivity exhibited anisotropy indicating preferred orientation of aggregates formed in situ.

This paper describes the results of the study on the effect of extrusion conditions on gloss of rigid PVC profile. Extrusion variables investigated in this study are: extrusion melt temperature, extruder temperature settings, extrusion rate and the die/sizer metal surface condition. It is hoped that this information will help PVC profile manufacturers to optimize their process for achieving desirable gloss.

This paper describes various techniques for assessing gloss of PVC extrusion. It discusses the effect of the incident light angle on measured gloss values and test sensitivity for PVC extrudates. It also describes the relationship between surface gloss and extrudate roughness, analyzed by scanning electron and optical microscopy. Finally, this paper provides recommendations on the most suitable methods for assessing gloss of PVC extrudates.

The properties of laminated films made from soy protein isolate and corn-zein are investigated. Plasticized corn-zein protein mixture was laminated on one side of a preformed soy protein film to modify the moisture barrier properties. The 250 ?m thick laminated films were dark-yellow, translucent, and somewhat brittle. The water vapor permeability values of these laminates were lower than those of the single component soy protein films. The tensile strength of these laminates was about 5 MPa. Continuous hot-roll film extrusion was also conducted and the process is being refined.

Blow molding is a thermal process involving heat and plastic resin. The blow molding machine heats the plastic pellets to a uniform temperature, through the function of heater bands and the friction of the screw, thus forming a homogenous melt that is shaped to a circular tube called the parison. The parison is then placed in a female blow mold that is cooled or heated via a turbulent fluid. Too much heat or too little heat, or too much cooling/heating at the wrong place or the lack of uniformity of heat/cool will cause many production problems. The machine plus the mold continuously strive to maintain these heats/cooling functions, but it is a precarious struggle. Unfortunately, you cannot see the thermal energy, only its effects. Thermal energy radiates in the infrared spectrum, outside the spectrum of visible light, which we rely upon in our daily lives and of course our blow molding environment.

Devolatilization is a key-step in polymer processing. Low-molecular-weight components are removed from a polymeric system. The transport of these components takes place by diffusion and in some cases by foaming. In this study the different transport phenomena are investigated independently from each other in a special designed apparatus. The transport in thin films and rotating pools with surface renewal is measured for different parameters. For the diffusive transport a high surface renewal rate and thick films enhance the mass transfer. For foam devolatilization the conditions for bubble nucleation and foam formation are investigated. The bubble nucleation takes place in the rotating pool in the area of high shear velocity.

Momentary Mold Surface Heated Process is a invention which heats only the mold surface over 400°C in few seconds with gas flame and cool it down very quickly again. Practically it was tried to produce a shiny surface of 98% light reflecting of the injection molded article of 30% glass fiber reinforced Polycarbonate. And it was carried out successfully with a simple attached equipment and specially designed mold so called MmSH Mold which is to supply the gas fuel and air between the two parts of mold. The results and method of wonder injection molding with MmSH Process was reviewed in this paper.

The evaluation and development of validated models for the nonlinear viscoelastic (VE) behavior of materials is an important area of research which has impact on a number of industrial processes including those in the food industry. Various nonlinear VE models have been developed over the years and evaluated for petroleum-based polymers; however, our understanding of the nonlinear VE behavior of biopolymers of industrial import lags our understanding of synthetic polymers. In the work reported herein, the nonlinear VE behavior of suspensions (20 % by weight in deionized water) of defatted oat flour, oat bran, barley flour, and oat flour were investigated. The rheological properties were measured using a Rheometrics Series IV controlled-strain rheometer equipped with a cone and plate fixture. The measurements were conducted at 23 ± 0.1°C. The rheological data were interpreted using a strain separable K-BKZ type (Wagner) model. The K-BKZ model was found to provide an accurate description of the rheological behavior of the four flour suspensions.

Thermotropic Liquid Crystalline Polymers (TLCPs) possess the lowest oxygen and humidity permeabilities among commercial polymers. However, TLCPs are highly incompatible with conventional polymers (polyolefins, polyesters), due to their unique composition and morphology. To compatibilize TLCPs with conventional polymers, a variety of polymers were evaluated having various functional groups like maleic anhydride, epoxy, acrylic acid etc. Using Ethylene Glycidyl Metha Acrylate (EGMA), three and five layer films containing TLCPs were prepared by conventional coextrusion. Experimental results have shown that a 10 ?m TLCP layer with polypropylene or polyester, increased the barrier to oxygen by a factor of 120 compared to neat polypropylene and by a factor of 40 compared to neat polyester, respectively. Furthermore, five layer films demonstrated higher barrier and stiffness properties compared to three layers films having identical overall composition. These unique barrier properties of TLCPs containing multi-layer films can compete commercially with EVOH and PVDC containing coextruded films, and can be further shaped by thermoforming and blow molding for high barrier packaging applications.