SPE Library

Strain softening in semi-crystalline polymers, is one of their most important viscoelastic characteristics and these materials are very sensitive to temperature and strain rate. A new phenomenological model with strain, strain rate and temperature dependence on stress was developed based on the G’sell & Jonas model with a new expression used to predict the strain softening phenomena, completing the whole mechanical behavior of polymers from initial strain, strain softening and part of the strain hardening. Model verification was performed on four materials and it was developed to further study the complex deformation patterns in thermoplastic materials subjected to impact loads

In recent years, injection molding technologies have been developed which use variable mold heating and cooling to increase part quality without significantly increasing cycle time. These processes are not suited for simulation with a conventional steady-state (cycle-average) mold thermal analysis. This paper presents the development of a new 3D finite element based transient mold cooling simulation capability which includes coupling the mold thermal solution with the mold filling and packing simulation. The predicted transient mold temperatures are validated against measured mold temperatures for two instrumented injection molding trials.

Nanoclays have to intercalate and exfoliate. The extent of intercalation and exfoliation is not understood by the processing industry. Researchers have to develop and nanoclay manufacturers have to supply a product which can intercalate and exfoliate to achieve the desired performance of the final product. The nanoclay powder which is supplied has a BET surface area of 5m2/gm or less. To disperse such a powder from 5 to 750m2/gm is difficult. To salvage such a situation, there has been a relook at minerals which are platey such as talc and mica. The finest talc supplied in the world has a BET surface area of 15m2/gm. It is possible to further grind this talc (also mica) along the basal cleavage to 100m2/gm to 200m2/gm. Such talc, if added to polymers can improve properties.

The substitution of plastic for more traditional materials stems from its reliability and affordability. However, with the heightened awareness on sustainability, plastic from fossil sources are sometimes perceived to adversely impact the environment. In an effort to address this issue, a detailed life cycle assessment of heavy duty sacks made from metallocene polyethylene (mPE) has been completed. The sacks are used in packaging powdered products for the construction industry. The results show that these sacks have several positive attributes and in many instances, may be a preferred alternative from a sustainability perspective. In fact, in manufacturing, transportation and handling mPE sacks are shown to consume significantly less energy and emit less greenhouse gas than paper-based alternatives. Additional environmental benefits will be discussed.

The objective of this paper is to discuss unique part and mold design requirements for high volume, cost competitive compression molding of carbon fiber reinforced epoxy (CF/E) uni-directional prepregs (UD). The typical part and mold design for compression molding of chopped fiberglass reinforced polyester sheet molding compound (SMC) will be used for comparison. Information that can be used as a design and processing guide for composites engineers involved with the development of high stiffness and strength CF/E for application in the transportation industry will be shared.

Polymaterials has developed a new high-throughput compounding (HTC) technology which generates thermoplastic formulations and DIN-ISO compliant test specimen accepted by engineers and the plastic industry. This technology accelerates the development of new compounds and is also much more cost-effective since only a fraction of material and time is needed compared to the conventional process. HTC not only increases the output significantly but also generates more insights enabling one to push innovation and to cut time to market for new products. The presentation introduces the technology and illustrates its capabilities by demonstrating several case studies.

In this study composite materials based on highdensity polyethylene (HDPE) with fillers containing nanostructures were prepared using melt mixing. Vapour Grown Carbon Fibers (VGCF), multiwalled carbon nanotubes (MWCNT) of the types Baytubes® C150P and NanocylTM NC7000, anthracite powder, microsilica, organoclay and expanded graphite (EG) as well as mixtures of these fillers were used. The amount and mixing ratios of the hybrid filled systems have been varied to determine the effect on the achievable level of thermal conductivity as measured on pressed plates. The filler dispersion and phase adhesion were studied using scanning electron microscopy. When limiting the maximum filler content to 10 wt%, the highest enhancement in thermal conductivity by 166% was found for VGCF followed by a 1:1 filler combination of VGCF with EG (148%).

Long fiber thermoplastic (LFT) composite design studies often emphasize fiber content but are sketchy on fiber-orientation, fiber-matrix interface and mold design. In this paper we detail a comprehensive approach to designing with LFT materials. Specific examples are given. Carbon-fiber compounds were successfully substituted for die-cast magnesium parts by redesigning the metal part for injection molding. Tailored fiber architectures were achieved through strategic gate locations, as advised by Finite Element Analysis (FEA) and Mold Flow Analysis (MFA). Mechanical properties were enhanced through modified molding processes.

The use of pulsed cold water instead of tempered coolant is suggested to be a versatile and cost-efficient technique for the cooling of injection moulds. However, the advantages and limitations of such discontinuous cooling strategies are still a controversial issue. In this paper the behaviour of a discontinuous temperature control system is analysed with a particular focus on the reproducibility of the process and the realisable dimensional stability of the parts and compared to that of a continuous cooling. For the investigations both a conventional and a conformal cooling channel geometry are considered. It turns out that at high mould temperatures the warpage of the parts can be reduced by use of discontinuous cooling, but at the same time the reproducibility of the process is affected adversely. The regulation of the discontinuous cooling proved to be challenging especially in combination with conformal cooling.

Weld lines are formed during injection molding, when two flow fronts meet. They are often not avoidable in complex technical parts. Their presence reduces mechanical strength, especially in high performance short fiber reinforced materials. Evaluating the load of highly stressed parts requires accurate knowledge of the interrelationship between the type of weld line, its morphological structure and the resulting mechanical properties. This paper aims at the development of a simulation method which enables the mechanical properties of weld lines to be considered precisely in part design.

The plastic parts for a float-valve system were designed. In the design was considered the use of PET bottles as floating device instead of the regular spheres, in order to promote the reuse of this plastic container and to decrease plastics residues. Additionally, the part thickness was reduced to use less plastic on the parts, and to decrease cycle times. All molds are two-plate and two cavities. The refrigerating system proposed uses U-shape channel, and the expulsion system is composed by ejector pins. Threaded connector´s mold is more complex due to require two-step opening.

The use of performance modeling is becoming more and more critical to the packaging industry. This trend is driven both by lightweighting efforts and the need to shorten package development times. The primary driver for reducing the amount of material used in packaging is cost reduction, with environmental positioning an ancillary benefit. However, it is critical to not compromise the shelf life or creep performance of the package, particularly in regions of the world with temperature extremes. This paper will explain key elements necessary for precise modeling of package shelf-life performance. The mathematical models considered are M-RULE® Container Performance Model and Virtual Prototyping™ Software. Some examples of how computer modeling has been applied to optimize package performance will be discussed.

The conventional control of the injection moulding process is based on machine variables, which cannot sufficiently characterise the course of the process. Hence, a system that controls the injection moulding process based on process variables has been developed at the Institute of Plastics Processing at RWTH Aachen University during the last years. The concept of the self-optimising injection moulding process is based on this research. This paper describes the concept of the self-optimising injection moulding process during the holding pressure phase and the idea of an extension by an incremental cooling system using small-sized cooling areas.

The general aim of the Cluster of Excellence “Integrative Production Technology for High-Wage Countries” is to overcome the actual contradictions between value- and planning-orientation as well as between scale and scope in production technology. One important aspect of this approach is the development of virtual production systems to increase simulation accuracy and thereby to reduce development times and costs as well as to optimise the utilisation of material. In this paper new developments in the field of the calculation of molecular orientation are described and a validation with different experimental measurements is presented.

Miniaturization and individualization are some of the current and in future ongoing trends in producing business in general and they also are influencing the plastics processing industry. To meet the upcoming challenges a lot of research is being done in the field of micro-extrusion. This work investigates a method to identify the phenomenon of extrudate swelling of micro extruded polypropylene using an optical analyzing method. Experimental data varying the pressure is presented and an optical analysis is explained. The results show the suitability of the method but reveal that some more experiments have to be done in order to formulate clear statements.

This paper presents a 3D numerical model to analyze the melting process in a single-screw extruder. The fundamental equations of fluid dynamics are solved using the Finite Volume Method. The software Fluent distributed by ANSYS, Inc. was used for the numerical calculations. The computing domain is a helical-shaped screw channel. The solid bed is modeled as a fluid with a very high viscosity by adjusting the formulation of the Carreau model for temperatures below the melting temperature. The model predicts the melting length, pressure build-up and the velocity and temperature distribution within the channel.

There has been much research in the biomodeling of human blood vessels. Models of human blood vessels can be used for aids in future research of new medical devices that can be preliminarily tested in an in vitro setting and that could potentially lead to breakthroughs in the medical device industry. There is also the possibility to use such models for the training of surgeons, especially for complex operations, analysis of arterial diseases, and to provide the basis for hemodynamic studies. Within the last two decades accurate models have been fabricated using corrosion casts obtained from cadavers and the lost wax process. Recently, there has been a trend towards replicating the properties of blood vessels more accurately. The use of hydrogels has the potential to achieve this, as it is possible to represent properties such as viscoelasticity, anisotropy, and lubriciousness, all of which have been shown to be present in human blood vessels. The goal of this study is to apply casting methods to a core, which represents similar tortuosity and dimensions to a section of blood vessel, and achieve a low cost model that will represent the dimensional accuracy as well as representing physical properties of blood vessels as accurately as possible. In order to achieve this, poly(vinyl alcohol) (PVOH)/poly (acrylic acid) (PAA) hydrogels were chosen as a material that has the potential to match the properties of blood vessels. The PVOH/PAA hydrogels were prepared using a freeze/thaw processing technique.

In the presented project a new coating plant for large area microwave (2.45 GHz) excited low pressure plasma coating with substrate bias has been designed, which allows the coating of foils up to a size of 300 * 300 mm². The objective of the research work is to characterize the effects of the process parameters on the properties of plasma-polymerised coatings, particularly regarding their behaviour under strain. Investigations are carried out using a microwave plasma source and polyethylene terephthalate (PET) as substrate material. As layer forming monomers for plasma polymer barrier coating of the substrates are used.

Recently advances in research and manufacturing techniques of biocomposites have allowed the car manufactures to use bio-composite in various applications. Biocomposites are fast emerging as viable alternative to traditional materials due to their low cost, lightweight, good mechanical performance and biodegradable properties. ECOSHELL project (Development of new light high-performance environmentally benign composites made of bio-materials and bio-resins for electric car application) proposes to achieve a full bio-composite made of high performance natural resins matrices, resulting in the use of totally natural, environment friendly composites, with enhanced strength and bio-degradability characteristics designed for the electric car.

Silver is a known antimicrobial agent, and has found use in protecting a range of products against bacterial growth. The inherently large surface area of silver nanoparticles allow for a high release rate of silver ions to the environment, where they can be active against a wide range of microbes. Herein, we report a new method of producing silver nanoparticles using a plasma furnace. This process easily allows for the support of the nano-silver material on micron-sized inorganic particles. Silver formed in this manner is more easily dispersed in polymer systems, while maintaining antimicrobial activity against gram positive and negative bacteria.