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.
Biaxially oriented polypropylene (BOPP) films with high oxygen barrier and high clarity were produced through the layer-multiplying, forced assembly process technique. 15-mil thick sheets with 33 alternating polypropylene (PP) / poly(ethylene oxide) (PEO) layers were coextruded and subsequently biaxial oriented at 135-150 ?§C. The biaxial orientation resulted in a layer thickness reduction from the microscale to the nanoscale. Crystallization of PEO was confined in the nano-layers where lamellae could only grow within a two dimensional plane. Highly in-plane oriented PEO lamellae improved the oxygen barrier by an order of magnitude. On the other hand, the films retained the high clarity.
Although they have only recently become a hot field of interest, aerogels were first developed by Kistler1 in the 1930's by supercritically drying a low solids suspension of colloidal particles. The resulting material was highly porous and possessed low thermal conductivity and low density. It is unsurprising then that aerogels have been used as thermal insulation, in applications ranging from personal footwear2 to battery pack insulation for a Mars rover3. The 'pearl necklace' nanostructure of aerogels, however, is inherently weak as demonstrated by their friability and brittleness. Only about 31 kPa4 of stress is required to completely shatter a native silica aerogel.
A design methodology has been developed for creating an improved flow passage in a flat die that distributes polymer extrudate across the width under a condition of uniform shear rate. This type of flow passage will spread any and all molten polymer materials uniformly regardless of the power law exponent value. This also results in a uniform residence time inside the die which allows for reduced changeover time and material waste. The new method achieves these results in a more compact fashion with reduced wetted area expanding the applications to wider widths than previous constant shear designs.
Prepreg composites offer many advantages over other types of composite materials such as low void content, control of fiber volume fraction, control of laminate thickness, and others. Nanoparticles have shown to improve mechanical properties when incorporated into composite materials. Incorporation of nanoparticles into prepreg materials can be very challenging if not done at the prepreg fabrication stage. In this study, a novel method of incorporating nanoparticles into prepreg composite materials was explored. This new method allows for selective reinforcement of the prepreg material at critical areas such as stress concentration locations. Surface abrasion and open hole tensile properties of the composites were measured.
As electronic devices tend to slimmer and more integrated management of heat transfer in devices become a big task for device design. Metallic materials are widely used for heat dissipation materials but there are many attempts to replace the metallic materials with highly thermal conductive thermoplastic composites due to their lightweight and economic manufacturing cost. Intrinsically polymers are thermally and electrically insulator but they can turn into thermally conductive material by compounding with thermally conductive fillers such as graphite ceramic filler carbon black carbon fiber or carbon nanotube (CNT). In this research strong correlation of shape of graphite on thermal conductivity was investigated in polymer/graphite composites.
As electronic devices tend to slimmer and more integrated, management of heat transfer in devices become a big task for device design. Metallic materials are widely used for heat dissipation materials, but, there re many attempts to replace the metallic materials with highly thermal conductive thermoplastic composites due to their lightweight and economic manufacturing cost. Intrinsically polymers are thermally and electrically insulator, but they can turn into thermally conductive material by compounding with thermally conductive fillers such as graphite, ceramic filler, carbon black, carbon fiber, or carbon nanotube (CNT). In this research, strong correlation of shape of graphite on thermal conductivity was investigated in polymer/graphite composites.
Micro-injection moldings were obtained for high density polyethylene (HDPE), to study the effects of processing conditions on the microstructural characteristics and mechanical properties of the moldings. Various microstructural features, such as skin-core structure, skin layer thickness fraction, and distribution of crystalline shape and size, were observed under different processing conditions and analyzed and compared to observations made with poly(oxymethylene) (POM). Process-structure-Youngƒ??s modulus relationships were analyzed by considering the effects of skin layer thickness, average plunger velocity. Suggestions for mold design were proposed on the basis of polymer melt flow behaviour.
Injection molded automotive parts usually feature high flow length to wall thickness ratios. In order to ensure low cycle times, tooling costs and scrap rates, the respective material formulations should have a high flowability. Reducing the viscosity, however, also affects the materials' morphology and mechanical properties, especially the impact strength. To quantify this effect high impact reactor-thermoplastic polyolefins (rTPOs) consisting of polypropylene (PP) blended with in-reactor made ethylene-propylene rubber (EPR) were prepared and tested. Particular attention was paid to the influence of the ethylene-propylene rubber's composition, i.e. comonomer ratio and molecular weight, on application properties of such rTPOs like toughness, surface gloss and scratch resistance.
It would be of great value to develop dependable strategies for the control of part weight. Based on the Pƒ??Vƒ??T (pressureƒ??volumeƒ??temperature) behavior of the polymer, a Pƒ??T (pressureƒ??temperature) control method by cavity temperature was presented in this study. In the present control method, the total injection time is controlled by cavity temperature instead of time, the relationship between pressure and temperature can be controlled. The experimental results revealed that the Pƒ??T control method by cavity temperature yields a much better part quality and uniform part weight than conventional control method.
Fracture mechanics lifetime and safety assessment of pressurized polyethylene (PE) pipes is based on the knowledge of material specific creep crack growth (CCG). However, with common test methods the investigation of this failure mechanism is not possible in modern PE-pipe materials in a feasible time. For an accelerated generation of CCG an extrapolation concept based on fatigue tests with cracked round bar (CRB) specimens was developed. In the present work this concept was applied to a common PE-pipe material to generate the material specific CCG data within a few weeks. To evaluate these data a fracture mechanics lifetime prediction of the CRB test was compared to results from static tests. With the integration of the data into a lifetime prediction model for pressurized pipes a simulation of a real pipe was possible.
Ultrasonic plasticizing allows the melting of very small amounts of polymers for micro injection molding. The ability to plasticize polymers with ultrasound arises from the effect that they heat up under cyclic deformation due to inner and outer frictional losses. This paper presents investigations on the course of heating during plasticization. The heating rate as well as the corresponding process data of the ultrasonic equipment is analyzed in dependence on the parameter settings. Example micro parts being molded show the possibility to use ultrasonic plasticizing as a production technology.
One of the most attractive environmentally friendly energy generation methods is wind power. In order for this technology to compete favorably with the cost of traditional energy generation methods, the wingspan needs to be greatly increased from current dimensions. For this to occur, we need to take advantage of new material developments such as nano-composites.In order to manufacture such large parts, we need to understand factors affecting flow. In the case of flow through porous media, the material properties are permeability and viscosity. In this work we present preliminary results on the effect of carbon nano fibers on permeability.
During service, thermoplastic parts are often subject to a combination of thermal and mechanical loads. Especially the temperature has a great influence on the stiffness and the specific volume. Consequently the thermal exposure has to be considered during the design process of thermoplastic parts. This paper describes the modeling of the temperature-dependent viscoelastic material behavior. Because the determination of the required thermal and mechanical properties is cost- and time-intensive, a procedure is elaborated to depict the temperature-dependent long-term behavior on basis of short-time tensile tests. Finally the model is evaluated in a comparison with experimental results.
In the current economic market, production efficiency is critical if manufacturers are to remain competitive. The largest part of the cycle in injection molding is the cooling time. Thus for injection molders, to be successful, it is extremely important that they minimize this part of the process without adversely affecting part quality. Predicting the minimum safe cycle time in injection molding is complicated by the cyclic nature of the process. The mold thermal state changes with continuous molding until a quasi steady state is achieved.In this work, we evaluate the minimum frozen layer thickness required before the part can be demolded and how the growth of this frozen layer is affected as the mold thermal state changes with continuous molding cycles. Experiments are used to relate the minimum frozen layer thickness to dimensional stability and to select an ejection criterion in order to obtain a minimum safe cooling time
In the co-injection molding process, sometimesreferred to as sandwich molding, two different polymermelts are either simultaneously or sequentially injectedinto a mold to form a part with a skin/core structure. Coinjectionmolding offers the flexibility of using the bestproperties of each material to reduce material cost andpart weight. Particularly, it allows, the use of recycledmaterial in the core without an adverse effect on surfacequality. The properties of a co-injection molded productdepend on the individual properties of the skin and corelayers, and the skin/core volume ratio. This paper presentsa study of the effect of molding parameters on materialdistribution and mechanical properties of co-injectionmolded plates. Two virgin materials were triedpolypropylene (PP), and thermoplastic polyolefin (TPO)as well as grinded TPO from plastic bumpers.
The mechanical properties of PET bottles are significantly affected by the process. In order to precisely model the structural performance of these bottles, the wall thickness and the process dependent material properties have to be considered. This paper describes an approach to combine the structural analysis and the process simulation. The wall thickness distribution and the local stretch ratios of the blown bottle are calculated by a process simulation and are then transferred to the structural analysis. Thereby, the stretch ratios are correlated with stretch ratio dependent material properties. In cooperation with Nestl?? Waters M.T., Vittel, France, the approach is applied on an empty and filled 0.5 litre PET bottle. The investigations point out that the accuracy of the structural analysis is significantly improved by applying the integrative approach.
Using linear elastic fracture mechanics concepts a simulation methodology for the assessment of internally pressurized pipe lifetimes was developed. The concept is based on the numerical calculation of stress intensity factors for pipes under different loading conditions and on using experimentally generated creep crack growth kinetics for lifetime calculations. Comparison of simulated lifetimes with experimental data from tests with internally pressurized pipes proved the principal applicability of the concept but also identified major parameters affecting pipe lifetime.
Using linear elastic fracture mechanics concepts a simulation methodology for the assessment of internally pressurized pipe lifetimes was developed. The concept is based on the numerical calculation of stress intensity factors for pipes under different loading conditions and on using experimentally generated creep crack growth kinetics for lifetime calculations. Comparison of simulated lifetimes with experimental data from tests with internally pressurized pipes proved the principal applicability of the concept, but also identified major parameters affecting pipe lifetime.
In the production of polyurethane parts the use of nonpermanent release agents is still inevitable. The regular mold-cleaning of residua of the release agent reduces the efficiency of the production process considerably. This paper describes the development of a permanent plasma-induced release coating with high durability for the series production of PU-parts as a surrogate for conventional non-permanent release agents. Basis of the project is a plasma-polymeric gradient layer with highly crosslinked siloxane-compounds for the mechanical strength of the coating and a high density of methyl groups towards the PU-sided surface for excellent release properties.
For a fracture mechanics lifetime assessment of pressurized polyethylene (PE) pipes the knowledge of the material specific creep crack growth (CCG) kinetics is essential. As testing of CCG with common test methods is not possible in feasible times, an accelerated extrapolation procedure based on fatigue tests with cracked round bar (CRB) specimens was developed previously. Within the present work this test procedure was used to characterize CCG of a PE material at elevated temperatures of 60?øC. In combination with a numerical simulation model for pressurized pipes, lifetimes were predicted and correlated to real pipe failure times of the same material.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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