The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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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.
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.
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.
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.
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.
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.
Low-density plank foam products were developed from both conventional and high melt strength (HMS) polypropylene resins. Bubble stability was achieved by making the foam density low and the cell size small. The use of a multiple-orifice die with an optional use of forming yielded a plank foam product with a large cross-sectional size.
A technique for measuring the cutting properties of thermoplastic sheet using steel rule dies is presented. This technique can be used to evaluate the roles of die hardness, point size, temperature, and bevel as well as sheet thickness and temperature on cutting efficiency. The technique is demonstrated using oriented polystyrene and amorphous polyesters such as PET and PETG. The cutting mechanisms for these materials are examined by controlling the penetration depth of the steel rule die in order to create a series of partial cuts.
Business-to-Business e-commerce has even greater potential than consumer focused e-commerce. We currently are in a transition from the Industrial Age to the Information Age. E-commerce is introducing new business models in many industries. This paper will describe how and why that is as well as how you can harness the power of the Internet as part of your marketing strategy and business development tools for the next decade.
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.
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.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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