SPE Library

The chemical resistance of polyethylene (PE) for pipe applications was investigated with special regard to physical and chemical material aging. Therefore, tensile tests were conducted on films which were exposed to two different aggressive media for different predefined periods of time and at two different temperatures as well as on films which were not exposed to the media. The impact of the media on the Young´s modulus E, the stress at yield σy, the strain at yield εy and the strain at failure εf were studied. Potentially physical or chemical material aging was investigated by the degree of crystallization, the Oxidation Induction Time (OIT) and via Infrared (IR)-spectroscopy.

IMPRESS targets the development of a technological injection moulding platform for serial production of plastic components incorporating micro or nano scale functional features. The platform is based on most advanced facilities divided in three modules: - tool manufacturing | involving different technologies of micro- nano direct manufacturing | from top-down to bottom-up such as self-assembling, - injection moulding | including equipments fitted with innovative hardware technologies to improve replication quality and capability, - intelligence | dedicated to advanced process control and online metrology integration. Beside this large panel of facilities | three case studies will be presented for biology | medical and energy applications. We present the main results obtained during the first year of the project.

The manufacturing of thermoplastics parts needs a cooling phase to give the shape to the part. In injection molding | cooling can represent more than 70 % of the total cycle time. This is the reason why cooling channels have to be designed with great care in order to meet quality with efficiency requirements. In this paper | we propose a methodology to optimize the geometry parameters and coolant temperatures of the channels based on the use of modeFRONTIER® software combined with the injection molding simulation software MOLDFLOW®. Multi-objective optimisation will be carried out with criterions based on quality and cycle time minimization.

Weathering and light exposure are important causes of damage to coatings | plastics | inks | and other organic materials. This damage includes gloss loss | fading | yellowing | cracking | peeling | embrittlement | loss of tensile strength | and delamination. For many manufacturers | it is crucial to formulate products that can withstand weathering and light exposure. Accelerated weathering and light stability testers are widely used for research and development | quality control | and material certification. However | the importance of outdoor testing cannot be overlooked. Accelerated testers provide fast and reproducible results. The most frequently used accelerated weathering testers are the fluorescent UV accelerated weathering tester (ISO 4802-3 | ASTM G154) and the xenon arc test chamber (ISO 4892-2 | ASTM G155). In recent years | low cost and easy-to-use testers have been developed. This paper compares two accelerated weathering test methods: fluorescent ultraviolet and xenon arc. The paper will describe the strengths and limitations for both techniques due to: simulation of the forces of weathering | including sunlight | temperature and moisture | mounting of test specimens | control of test parameters | and operational considerations.

The failure of a mould-part used for hot-forming is investigated. The die | made from AISI H13 steel was intended for the production of plastic cups. The mould-part exhibited a | single uniform crack through thickness | after five millions working-cycles | whereas it’s predicted working life was ten millions cycles. Data were collected regarding the material selection | manufacture and operational history. The die was optically inspected. Hardness measurements were carried out and chemical analysis was performed. Detailed optical and scanning electron microscopy observations suggest the type of failure and the factors that led to it.

Tyres consist of synthetic rubber | metals and linen. Tyre waste decomposes after hundreds of years | and its presence is detrimental for the environment. Standing water | trapped into tires may be a permanent pollution source | while tyre waste next to a forest increases the possibility of fire. European legislation imposes the recycling of tyre waste | which includes the following three steps: shredding in strips | cutting strips in small pieces | and powder production from the pieces. At the last stage magnets remove the metallic pieces | while centrifugal screens remove the linen. Metals are sold to the steel industry as scrap | linen is used in limekiln as a combustion material and the rubber flakes are used in numerous applications (e.g. road surface construction, concrete additives | mouse pads | etc.).

A wide range of PE materials | including LLDPE, HDPEs and LDPE were used for preparation of the blown films. By changing processing conditions | different structures for these blown films were produced and their structural parameters investigated. Establishing fundamental /structural model between structural parameters and tensile modulus of blown films was the objective of this work. A model for the tensile modulus was proposed and correlated to some structural parameters including crystallinity | orientation factors for crystalline c-axis and amorphous phase | lamellar thickness and crystal size. The measured modulus and calculated one were compared and a reasonable agreement was found between them.

Plastic Laminated Object Manufacturing has not been assessed from the flexural properties point of view. The deflection range in parts manufactured by this technique is wider than in parts fabricated by other additive manufacturing methods like SLS or FDM. This fact has increased the interest on the final application of these parts rather than restricted to Rapid Prototyping applications. In this study it will be compared the impact of building orientation and geometric features of parts over the flexural properties. Through optical observation it will be studied the failure mechanism

New injection processes have been developed last decades, improving the designer freedom in order to launch attractive functionalities. All these procedures should be carefully analysed before to decide their use, because it is necessary to understand their natural restrictions, cost and operation requirements and rheological implications in the tools construction. This contribution presents a wide study made in the T.I.I.P., research group from the University of Zaragoza, which gives simulation results and experimental values about sequential injection moulding, and some practical considerations for designers and toolmakers, in order to get successfully results.

The Kinetics of acetaldehyde (AA) stripping from PET pellets were determined at different temperatures, along with the determination of the residual concentrations of other less volatile compounds such as 2-methyl-1,3-dioxolane (2MD). The rate constants for the polymerization and AA diffusivity coefficients were determined at different temperatures of air stripping of PET. The air stripping of AA from PET is shown to involve chemical reactions and physical changes including polymerization, diffusion and generation of AA, 2MD, EG and water. This paper discusses the mechanisms of the chemical reactions and the formation of the by-products. The techniques used to elucidate the mechanism include gas chromatography (GC), intrinsic viscosity (IV), and density.

Effectively feeding low bulk density material into a co-rotating twin-screw extruder has always been a challenge. However with the introduction of even finer particle size fillers (sub-micron in some cases) as well as new generations of polymer reactor resins, the issue has become even more problematic. Additionally as bulk density decreases, the materials tend to fluidize more easily. Fluidization lowers the “effective” bulk density even further and exacerbates feeding issues. Typical unit operations within the compounding process where material is more susceptible to fluidization are: transfer from storage vessel to feeders, from feeder to twin-screw extruder and within the feed zone conveying section of the twin-screw extruder. While there are methods to minimize the potential for fluidization such as dense phase conveying from storage to feeder, minimization of the feeder height above the extruder feed opening, incorporating a vent into the feed hopper, extending the length of the conveying zone in the extruder feed section, the process eventually reaches a feed volume limitation, which more often than not is well below an economically viable production rate. This paper will review a new Feed Enhancement Technology (FET) that provides significant improvement for the introduction of fine particle / low bulk density materials into the extruder.

The co-rotating fully intermeshing twin-screw extruder is the primary production unit for compounding of polymer based materials. It also has had a long term presence in processing material in the chemical and food industry and more recently in pharmaceuticals. While this equipment celebrated its 50th anniversary several years ago and might be considered a “mature” technology, it has not experienced a decline in new developments as might be expected, but rather a significant number of advancements continue to evolve. This paper will highlight several significant developments of the past 10 to 15 years. These are the implementation of high torque (power) designs, the use of increased rpm in conjunction with high torque for improved operating flexibility and productivity, and finally a technology breakthrough for feeding difficult to handle low bulk density materials.

The methodology is based on some conventional models for flow in the hopper, solids bed and melting zone. In the melt pumping zone the Hele – Shaw approximation is applied, which describes spreading flow in two dimensions. The momentum and energy equations are solved layer – by – layer starting from the barrel wall. This methodology enables significant reduction of computer time required for simulation of extruders with complex screw geometry, over the fully 3D approach. Good agreement was obtained with some available experimental data and further evaluations of predictive capabilities are currently underway.

Orthopedic procedures often require repair materials that can carry large loads without excessive deformation or failure. To this end, we designed composites using two biocompatible/bioabsorbable polymers, poly(L-lactic acid) (PLLA) and polycaprolactone (PCL). The latter was filled with nano-needles of hydroxyapatite (HA), while the PLLA was used in long-fiber form. Theory advises that the HA nano-needles must be of high aspect ratio and be aligned in the matrix to gain sufficient stiffness. We have explored several processing techniques for accomplishing this task, and have successfully made composites in the 8- to 10-GPa range. Variations of this structure will also be described.

This paper presents a novel technology to produce plastic parts called “Stages Moulding”. The patented technology allows producing plastic parts with complex shapes, from a wide variety of polymers, with excellent surface quality, reduced thermal and mechanical stresses and possibility to produce parts with reduced weights. This novel process uses cheaper moulds and equipments than those used in injection moulding. The specific characteristics previously mentioned make this technology very promising for the production of plastic parts for different markets. The paper explains the main characteristics of this technology presenting some real examples of parts produced.

This research work develops new methods to produce biodegradable starch-based trays for the purpose of replacing expanded polystyrene in the food packaging market. The starch based biopolymers present several drawbacks like poor mechanical properties and very high density. In order to overcome these drawbacks two research lines have been set up: blending thermoplastic starch with biobased reinforcements from agricultural wastes like barley straw and grape wastes, and testing the foamability of these materials with a Microwave-foaming method.

The traditional sharpening through the razor blade method employed in the fracture characterization of polymers creates plastic deformation at the notch tip, which affects the fracture toughness values. Recently it has been applied a technique based on femtosecond pulsed laser ablation, which removes material with almost no heat dissipation, preventing melting and thermal deformation of the surrounding area and without plastic deformation at the crack tip. In this work, the fracture toughness of polycarbonate was studied using the Linear Elastic Fracture Mechanics testing procedure at impact velocity, evaluating the influence of crack sharpening by femtolaser or razor blade sliding.

X-ray radioscopy is a technique in which a series of radiographies are acquired during an evolving process. The present study aims to investigate the mechanisms occurring during the reactive foaming process of rigid polyurethane (PU) foams in its liquid state. The work addresses a comparative study of in-situ pore growth determination in PU foams with and without nanoadditives (nanoclays), based on the mentioned technique and thus providing a valid methodology to investigate the foaming process in all its stages. The results confirm that nanoparticles addition modify the final pore size most probably based on a higher nucleation rate at initial stages.

Nanofillers are added to rigid PU foams to improve their mechanical properties, however this expected behaviour is not always found. A poor dispersion of the fillers is usually accepted as a possible explanation, but chemical interaction between matrix and fillers could also result in a reduction of the final foam properties. In this study, polyurethane rigid foams (with and without nanoclays) have been produced and characterized. Different dispersion techniques have been used. The experimental results suggested that chemical interaction between fillers and matrix plays a critical role in the mechanical behaviour of these type of systems.

This paper presents an investigation on the improvement of the thermal conductivity of polystyrene foams by using different types of carbon blacks as additives. Carbon blacks with different morphologies were used as IRblockers. To test the changes in the conductivity foams with densities between 20 and 100 kg/m3 were produced using the solid state foaming technique. The cellular structure and thermal conductivity were analyzed in detail. In addition the thermal conductivity was analytically modeled to study the influence of the different carbon black types on the heat flow by radiation. The best morphology to reduce the thermal conductivity has been detected.