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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New High Barrier, Oxygen Scavenging Polyamides for Packaging Applications
Honeywell International is currently developing high oxygen barrier polyamides based upon nylon 6 and blends of nylon 6 with amorphous nylons (PA6I,6T type). Significant improvements in oxygen barrier result from the introduction of a proprietary oxygen scavenger moiety (active barrier") and/or silicate nanoclays ("passive barrier"). The nanoclay is added during polymerization rather than in a melt compounding process which leads to improved barrier properties and lower haze levels in multi-layer films and bottles. These novel polyamides are suitable for use as high oxygen barrier layers in cast and blown film as well as for barrier layers in co-extrusion blow molded polyolefin based bottles and co-injection stretch blow molded PET bottles. They are part of a cost-effective multi-layer film/bottle solution for packaging oxygen sensitive products. When blended with nylon 6 amorphous nylon lowers the total crystallinity and may enhance adhesion to PET. These new high oxygen barrier nylons should meet the barrier requirements of many demanding packaging applications while continuing to offer desirable properties such as flavor barrier strength and toughness."
Time Dependence of Shear-Thinning of Polymer Melts
We analyze Non-Newtonian dynamic data of several polymer melts and find experimental evidence for the time dependence of shear-thinning. To summarize, viscosity is not just function of temperature, pressure and strain rate (or frequency), as is already well known, but also of time. We specify the experimental conditions to observe this phenomenon, and provide an analytical expression that fits the data very well. An interpretation of this time dependent behavior is presented. It is suggested that disentanglement" understood in terms of the dual-phase interactive model (EKNET theory) is responsible for the time dependence of viscosity. We stipulate that any desired amount of disentanglement can be induced in any polymer melt by the proper mechanical treatment specifically providing means to eliminate entropic mechanisms of melt deformation. This can be achieved by synchronizing the viscoelastic states of the dual phases for instance by a combination of the proper temperature rate and amplitude of shear deformation. It is shown that time dependence of shear-thinning can only occur below the temperature of stability of the network of interactive coupling interactions between conformers which we are able to associate with Tll Boyer's liquid-liquid transition. Practical applications to processing are discussed in a companion paper of this ANTEC meeting ."
Extrusion of Polymer Melts under Intensive Shear-Thinning Inducing Lower Pressure and Temperature Requirements
We have built an extension to an extruder line, which provides the means to submit polymeric melts, as they extrude out, to an intensive shear-thinning treatment by combining cross-rotational and shear vibration melt deformation. Experiments are conducted with two polymers, a highly entangled metallocene polyethylene and a general purpose extrusion grade polycarbonate. It is shown that, for both polymers, extrusion requirements for a given throughput, i.e. pressure and temperature, can be drastically reduced, by as much as 80°C for temperature, and, simultaneously by a factor 2-5 for pressure, when applying the new patented combined cross-rotational and vibrational means. We study the individual effect on shear-thinning of cross-rotation alone, and of cross-vibration alone, and also analyze their combined effect which results in drastically reducing pressure and temperature of extrusion at constant throughput. Applications are discussed, which range from the benefits of extruding melts and blends at lower temperature (when normal extrusion requirements would degrade one of the ingredients), or increasing throughput, to producing disentangled frozen-in resins, having much lower viscosity at given molecular weight, when extrusion under intensive shear-thinning is extended to much longer flow lengths.
Reduction of Viscosity of Polymer Melt by Shear-Thinning and Disentanglement : Rheological Criteria and Commercial Perspectives
Mechanical performance of polymers improves with molecular weight (MW). Unfortunately, melt viscosity and thus lack of processability also increases with MW. Recently, a method to temporarily reduce the melt viscosity without changing MW has been proposed . The method uses processing windows such that shear oscillation superposed on extensional flow at gradually increasing shear thinning amplitude are created by imposing conditions of strain, frequency and temperature that bring the melt (G'/G*) close to 0.75-0.85. The purpose of the present communication is to report results of a two-year research and development effort aimed at reducing the viscosity of several commercial resins using a pilot stage disentanglement machinery. The paper explores the commercial implications and answers the following questions: is it possible to shear-disentangle a large quantity of commercial resin at fast throughput, is it possible to process the disentangled melt before it regains its normal entanglement, and is it possible to speed-up the re-entanglement process after forming to regain mechanical benefits? From a laboratory and low throughput extrusion scale, the answer to all these questions is positive. The technology is presently being tested at a pilot pre-production scale to quantify the answers from a commercial perspective.
Measuring the Nonlinear Viscoelastic Material Properties of Thermoplastic Materials by Dynamic Mechanical Analysis (DMA)
As plastics are more and more used for high-performance application the design and material selection have to take into account the complex material properties. The lifetime of a product and the suitability of a raw material for a certain application can often only be estimated based on a huge data set of mechanical properties. Mechanical properties of thermoplastic materials are influenced by temperature, time and the level of loading. Thus, the engineer at least needs stress-strain-curves measured under varying temperatures and loading speeds to ensure an efficient product design. These measurement data are also required by software for simulating nonlinear visoelastic material behavior. Because of the costs of measurement the required data often are not available sufficiently. This paper describes first results of research aiming at generating the stress-strain-curves out of Dynamic Mechanical Analysis (DMA) measurement data. By help of DMA mechanical properties can be measured faster, more extensively and with lower costs than by tensile tests. prediction of product lifetime. Also it can reduce costs for product testing as models are able to simulate the effect of boundary conditions which in tests only can be realized with a lot of effort (e.g. changing temperatures, multi-dimensional stresses, changing loading speeds). However, material models base on measured material data. Every suitable model at least needs the data of several tensile tests.
Resistance to Erosive Wear by Copper Alloy Mold Components
Injection molds are increasingly making use of high strength, high thermal conductivity copper alloy mold components to reduce cycle time and improve dimensional accuracy. Molders are focused on the durability of these components. This paper is the first of a two-part discussion of erosive wear. Performance of standard copper alloys and tool steels was compared. Wear measurements were taken on a flat surface across from the gate, on the core side of the mold. Samples were run without release or lubrication aides, using 33% glass-filled nylon. Uncoated copper alloys were found to have comparable performance to that of pre-hardened tool steel.
Comparison of Various Hard Coatings to Protect Copper Mold Components from Erosive Wear
Demand for fast-cycle, dimensionally-consistent, thin wall parts molded from reinforced engineering thermoplastics continues to increase. The use of high strength, high thermal conductivity copper alloys has been limited by the perception that these alloys will not stand up to the wear of reinforced engineering resins. This is the second part of a discussion on the effects of erosive wear on copper alloy mold components. The ability of several chromes, electroless nickel, and titanium nitride to protect against erosion was tested. Several combinations of alloys and plating systems provided wear resistance that favorably compared to hardened H13 tool steel.
Environmental Stress Cracking of PC in Contact with Aqueous Solutions
The environmental stress cracking (ESC) behavior of some plastics is very well examined. Especially for polyethylene the mechanisms are nearly clear. For amorphous thermoplastics this mechanisms were examined in many researches, but are still not really clear. Especially for polycarbonat (PC) in contact with aqueous solutions systematic examinations of the ESC behavior are rare. In this paper examinations of the ESC behavior of PC in different aqueous solutions are presented. The tests were done by a medium-tensile-creep test. Different pH-values of water and a surfactant were examined about their influence on the ESC behavior. Also distinctive types of PC and their influence on the ESC behavior were examined. It is determined that the ESC of PC in contact with aqueous solutions is not only, like classical approach, controlled by physical effects. A large effect of chemical mechanism is also part of the failure mechanism.
The Effect of Pigment Type and Concentration on the Rheological Properties of Polypropylene
The rheological characteristics of a range of pigmented polypropylene (iPP) was investigated using dual capillary rheometry techniques, over the temperature range 190°C to 230°C and shear rate range of 10s-1 to 800s-1. The iPP was compounded with pigment masterbatch concentrations ranging from 0.2% to 3.0%, using a 38mm Killion compounding line. The pigment masterbatches investigated were iron oxide, titanium dioxide and phthalocyanine blue. The rheological data, showed that there were considerable increases in apparent viscosity of pigmented iPP even at relatively low pigment loadings. The increase in apparent viscosity was particularly evident over the lower shear rate range. Activation energies (Ea) calculated from the rheological data showed large increases in Ea for pigmented iPP especially at lower shear rates, suggesting crystallization of the iPP melt.
The Effect of Phthalocyanine Based Pigments on the Crystallinity and Mechanical Performance of Chill Roll Cast Polypropylene Extruded Sheet
The nucleating effect of phthalocyanine based pigments on the processing and properties of semi-crystalline polymers has been a challenge to polymer processors for many years. These effects are ever more pronounced during in-line, post extrusion processes such as elevated temperature drawing of polypropylene slit film tapes, for rope and twine applications. A range of polypropylene films containing levels of 2% phthalocyanine based pigments and inorganic iron (II) oxide based pigments were manufactured using the chill roll cast extrusion process, using a range of quench temperatures and die to chill roll gaps. Analysis of the tensile properties of the films showed significant increase in modulus for the phthalocyanine pigmented films by up to 25% in comparison to the iron (II) oxide pigmented and non pigmented films. DSC analysis showed the crystallinity of phthalocyanine pigmented films to be less affected by quench roll temperatures than the iron (II) oxide pigmented and non pigmented films. However polarized light microscopy analysis of the films showed the spherulite sizes for the phthalocyanine pigmented films to be significantly smaller than the iron (II) oxide pigmented films and non pigmented films.
Modeling of the Thermomechanical Behavior of Nonlinear Viscoelastic Materials under Multidimensional State of Stress
The thermomechanical behavior of nonlinear viscoelastic materials depends on time, temperature, loading rate and height of load. A model has been presented that allows the simulation of nonlinear viscoelastic materials under multidimensional state of stress. This 3-dimensional deformation model is built by parallel arrangement of a certain number of basic elements. Each basic element consists of an elastic Hookean element and a damper system (3D damper) to describe the viscous properties. The model is calibrated by isothermal strain rate controlled tensile tests at different temperatures. Along with suitable calculation algorithms, this model offers the ability to simulate any multidimensional load history caused by direct stresses and changing temperatures. The model allows the simulation both of quasi-static and dynamic loading at different temperatures . Building up on this model, modifications on the calculation algorithms are done to enable the simulation of thermally induced stresses in constrained geometries. For this reason the calibration of the model has to be extended. The thermal expansion coefficient is determined from non-isothermal zero stress experiments. Furthermore modifications on the biaxial testing device are started to be able to carry out non-isothermal, biaxial tests.
Failure Analysis of a Cracked Construction Vehicle Grille
Cracking occurred within grilles used on heavy construction equipment, without apparent cause. The cracking was observed to be sporadic and had initiated while the parts were being stored in a warehouse, prior to installation on the vehicles. The cracking was found adjacent to holes used to secure a logo nameplate in conjunction with metal bolts. The focus of this investigation was a timely determination as to the nature and cause of the failures. Of particular interest was whether the failure was primarily associated with material, design, processing, or environmental factors. This paper will document some of the testing performed to characterize the failure mode and identify the root cause of the cracking, in order to illustrate the failure analysis process.
A Study on the Processability of Polycarbonate in Solids Conveying Zone
For several bisphenol-A polycarbonate resins, pressure distributions along the screw channel have been obtained according to the transport theory in the solids conveying zone. Structure and properties of those resins are related to the pressure distribution and the flow rate. When the chemical structures, mechanical properties, and number average molecular weights are equal, the polymer with broader molecular weight distribution (MWD) shows both a lower glass transition temperature and a lower pressure distribution in the solids conveying zone in spite of the increased flow rate. The polymer with broader MWD also shows shorter melting length than the others. The numerically determined length of the solids conveying zone is used to correct the pressure distribution.
The Influence of Red Phosphorous upon the Flame Properties and Dielectric Properties of Glass Fiber Reinforced Nylon-66
Incorporation of red phosphorous into glass fiber reinforced nylon-66 composites not only confers good fire retardancy but also retains good dielectric properties. The flame retardancy of the red phosphorous filled nylon-66 composites increase along with their red phosphorous contents. However, their arc resistance and dielectric strengths decrease along with the red phosphorous content. Flame retardant experiments were performed to understand these interesting behaviors. Possible mechanisms accounting for these behaviors are discussed.
The Effect of Pigment Type and Concentration on the Mechanical Performance of Injection Moulded Metallocene Catalysed Polyethylenes
A linear Low density octene and hexene based metallocene catalysed poly(ethylene/? olefin) copolymer (mPE's) and conventional polyethylene of similar density were injection moulded using different pigment types and loading of 0.05% to 0.5%. The results for the metallocene polyethylenes show significant deterioration in impact properties by up to 14% at room temperature and up to 16% at -40°C, depending on pigment type and concentration. Increases in tensile and dynamic modulus were also found to be related to pigment concentration and metallocene alpha olefin co-monomer type. Differential scanning calorimetry studies also showed significant increase in the crystallinity in pigmented materials. Increases of over 500% in tensile elongation for metallocene PE resins over the conventional PE resins were recorded.
Numerical Calculation of Stresses in Film Blowing
Film blowing is the major process for producing thin plastic film. In recent years, many researchers have noted the strong relation between the film stresses and orientation at the frost line and the final film properties. In the current work, using the bubble kinematics and material properties as inputs, numerical calculations have been performed to obtain the stress profiles in blown film bubbles using a viscoelastic constitutive equation (PTT) and focusing on stress variations in the thickness direction of the film. The results indicate that the film stresses are higher in the external surface of the film, which may explain experimentally observed differences in crystallinity and morphology between the two surfaces.
Environmentally Friendly Plasticizers for Polyvinyl Chloride (PVC) Resins
There has been increased interest in developing alternatives to phthalate plasticizers used in the processing of polyvinyl chloride (PVC). This paper describes research on modifying the composition of vegetables oils such as soybean oil for use as primary plasticizers for PVC. Advanced computational chemistry and modeling studies have been conducted to correlate structures of modified soybean oil with their compatibilities in PVC resin. The new soy oil derived plasticizers have excellent plasticizing efficiency with significantly reduced migration and volatility. Properties and performance of the new modified soy oil compositions as primary plasticizers in typical PVC formulations are summarized and compared to those of a standard phthalate PVC plasticizer.
Permeability Prediction from Non-Destructive Imaging of Composite Microstructure
Knowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of permeability is difficult and time consuming. Numerical calculation of permeability from a model reinforcement can circumvent experimentation. However, permeability predictions often rely on a model reinforcement that does not accurately mimic the actual microstructure. A rapid, non-destructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. Actual microstructure information can be then used to improve the accuracy of the model and therefore the predicted permeability. Additionally, the influence on fiber volume fraction and microstructural variability on permeability can be systematically studied. In this work, binary images of the microstructure of a unidirectional E-glass/epoxy composite were generated from the low contrast OCT data through image de-noising, contrast enhancement and feature recognition. The resulting data were input to a lattice Boltzmann model for permeability prediction. Results show that the image processing induced alterations in fiber volume fraction and tow surface area have an influence on the predicted permeability. Level-set methods for image analysis were then used to process the images to binary images. Level-set methods offer image de-noising and feature recognition while preserving fiber volume fraction and tow surface area. The calculated axial and transverse permeabilities from the level-set images shows excellent agreement with experimental values.
A Concept for a Applied Dryer Control by Prediction of the Moisture Content of Dried Material
To produce high quality parts from hygroscopic plastic materials like ABS, PA, PC, PET, PUR, etc. it is mandatory to keep the moisture content of the processed material below an upper limit for the specific product. Otherwise, the residual water causes problems during processing and probably decreases product quality. As a result of an increasing pricing pressure on the plastic processing industries the productivity of the manufacturing processes became more significant. One way to increase productivity is to reduce the energy consumption of the process. Drying requires a lot of energy. Process parameters are set after specifications from the producer of the raw material. These parameters are independent from the moisture of the raw material. Consequently, this leads to a higher energy consumption than is necessary and to fluctuations of the residual moisture. There is no closed loop control to keep the residual moisture behind the dryer at a constant level. The main reason is that there is no economic unit available to measure the moisture content that works for all materials independent from colour, apparent density, etc. This work presents a way to keep the level of the residual moisture at a constant level. For that a model of the drying process is used.
Meltdown-Time Profiles of Vibration Welded Nylon 66 Compounds
Meltdown is an important vibration welding process parameter. This research experimentally measured the meltdown-time profiles obtained from nylon 66 parts vibration welded on a Branson Mini II linear vibration welder. The study examined the effect of material (glass reinforced and unreinforced nylon 66), process parameters (weld pressures) and weld geometries (butt, T-shaped and cup welds) on meltdown-time profiles. Experimental meltdown-time profiles compare favorably with theoretical profiles obtained from existing models. Additionally, the presence of moisture in parts, and uneven or excessive welding are detectable by observing meltdown. This suggests its potential as an on-line quality control parameter.
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