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.
Extrusion responses including impact resistance (mean failure energy,MFE) of the extrudate as a function of extrusion conditions and ester lubricant formulation were evaluated. Mathematical models were calculated using experimental design software facilitating prediction of MFE and melt temperature responses for hypothetical extrusion conditions and lubricant packages. Extruder response predictions are then used to define a process window for hypothetical lubricant formulations where two or more extrusion responses must be balanced. Paraffin, ethylene bisstearamide, and ester based systems are compared.
Elevated process temperatures can accompany current high extrusion rates of rigid poly (vinyl chloride). Various colored weatherable siding compounds were studied in the processing range of 193 C (380 F) to 227 C (440 F). The extruded compounds showed only minor color shifts due to increased melt temperatures. Outdoor exposure through 4 years in Arizona, Florida, and Ohio demonstrated typical color change, but did not exhibit significant color shift relating to the initial processing temperatures. The extruded samples from elevated melt temperatures did demonstrate reduced impact strengths prior to outdoor exposure. Florida and Ohio exposed samples lost impact strength throughout the 5 years of exposure, with the higher temperature processed samples continuing to show lower impacts over time.
Polyethylene is commonly extrusion coated onto a variety of substrates for use in food packaging applications. The greatest utility comes from using polyethylene as a sealant layer. It has been determined that extrusion temperature has a significant effect on the hot-tack and heat seal performance of polyethylene. In the resins evaluated, as extrusion temperature increased, hottack strength decreased while plateau heat seal strength increased. Characterization of coatings applied at various extrusion temperatures has revealed that changes in molecular weight and crystalline morphology determine heat seal and hot tack performance for polyethylene coatings.
It has been known that the properties of nanocomposites are dependent on the degree of dispersion of expandable smectites clays in the polymer matrix. The different states of dispersion are exfoliated, intercalated and immiscible systems. However we and others have demonstrated that within a single system, the dispersion is far from homogeneous. Here we investigate the effect of dispersion of clay in Linear Low Density Polyethylene (LLDPE) nanocomposite films. Cloisite 15A was used as montmorillonite layered silicate (MLS). MLS were precompounded with a carrier resin to produce a master batch. Films of 1 mil thickness were prepared by a blown film extrusion technique. The through thickness dispersion in different films was investigated using x-ray diffraction. The distribution of clays was observed by polarized optical microscopy. The effect of the dispersion on the glass transition of the polymer was studied by differential scanning calorimetry (DSC).
A range of EVA/m-LLDPE/EVA co-extruded films, with Polyisobutylene (PIB) content from 0-20% and Vinyl Acetate (VA) co-monomer content of 6, 12 and 18%, was manufactured using a Killion cast film co-extrusion system. The films were aged at 45°C for up to 28 days, to enable tack (cling) development. The results show that film tack strength improved significantly with ageing. Increased VA concentration in the surface layer also showed significant improvement in film tack strength. The film tensile strength, elongation and tear properties in both MD and TD were not significantly affected by increase in PIB concentration. However, increased VA content showed slight improvement in MD mechanical performance of the films, TD properties were relatively unaffected.
This paper presents a model that allows the determination of the permeability values of plastic multi - layer structures that may be coextruded, extrusion coated or laminated that fit the requirements of a specific food or beverage. The model includes the use of several data bases like plastic permeability data, food and beverage data related to maximum gain or loss of gases and plastic raw material costs.The computational algorithm combines automatically different polymers predicting possible multi – layer structures based on adhesion criteria, maximum number of layers and the achievement of food requirements. The different calculation routines in the model include pressure, temperature and relative humidity corrections, change of units, among others.The model predicted permeability values are compared against measured multi –layer structures for several barrier films, specifically, OTR and WVTR values.
The improvement of oxygen-barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET-BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass-transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold-drawn polyester could be regarded as a one-phase densified glass. This allowed an analysis of oxygen solubility in accordance with free-volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess-hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero-solubility) condition.
The water vapour transmission rate (WVTR) of carton boards can be critical in high performance packaging applications. The authors have developed moisture barrier paperboards using aqueous-based (water-based) emulsion polymers, and the results obtained with these materials are presented. These polymers include polyethylene terephthalate (PET), polyvinylidene chloride (PVdC), and styrene-based emulsions. A range of these coated and laminated carton boards were prepared using a hand coater to achieve a controlled range of barrier layer thickness (24-100 microns), and analysed for WVTR over a range of temperatures and relative humidities. In addition, some boards were pre-coated with a primer coat before the application of the barrier topcoat, to investigate the effect of carton board topography on the moisture barrier properties. Low WVTRs in the range of 5-10 g/m2/day were achieved using several of the emulsion polymers, and it is clearly shown that by precoating the surface of a board with a primer before applying a barrier coat can lower the WVTR further even with a thinner overall layer of coating. Anisotropic characteristics of boards coated on one side only are clearly shown, with lower WVTRs always being achieved when the coated side of the board is adjacent to the higher humidity.
Films were prepared from a range of mPE resins of various comonomer types (hexene and octene), using a Killion blown film extrusion system. The films were manufactured at a constant blow up ratio of 1.6 by maintaining constant haul off speeds and screw speeds to give a uniform thickness of 50 microns. To effect the change in frostline height the rate of cooling was changed. Tensile analysis of the samples showed that modulus and tensile stress were related to both comonomer type and polymer density and that frostline height variation had an effect on the final film properties. DSC analysis showed that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type.
In this work, the performance of a new in-line scanning camera system for the study of bubble instabilities in film blowing extrusion is presented. Three commercial film grades, metallocene catalyzed linear polyethylene (LmPE), LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating the various bubble instabilities such as draw resonance, helicoidal instability, frost line height (FLH) instability are proposed. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of take-up ratio (TUR), blow-up ratio (BUR) and frost line height. It was found that the new system can capture the main characteristics of all bubble instabilities quantitatively. It was also found that the magnitude and periodicity of radius variation during draw resonance of LmPE is decreased as TUR is increasing at a given FLH and BUR implying that the origin of draw resonance in film blowing seems not to be the same phenomenon that the one observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the center of the die decreases as TUR is increased.
Converters often overlook the lowly wound roll of blown film as an incoming raw material requiring quality specifications. The film’s layflat uniformity is critical to printing, laminating, and sealing operations. This presentation focuses on the impact of melt temperature variation during film extrusion, and covers:How excessive melt temperature variation affects film and layflat quality.Some of the causes of melt temperature variation.The basics of setting up temperature profiles – speaking to the screwHow to read temperature controllers – listening to the responseHow to measure and track screw performance – are we communicating?
Films were prepared from a range of conventional and metallocene polyethylene (mPE) resins of various comonomer types (butene, hexene, octene), using a Killion blown film extrusion system. The films were manufactured using blow up ratios (BUR) 1.3 – 2.5, haul-off rates, and screw speeds to give a uniform thickness of 50 microns. Tensile analysis of the samples showed that modulus and elongation were related to both comonomer type and polymer density. The mPE resins showed considerable improvement in mechanical performance compared to conventional PEs. Differential Scanning Calorimetry analysis showed that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type.
A model is developed for the film blowing process including the effects of viscoelasticity, flow-induced crystallization and bubble cooling. A molecularly based constitutive model is coupled with the macroscopic balance equations. The ability of the model to accurately predict velocity and temperature profiles along the film line given the bubble shape (currently from experimental data) is demonstrated. The macroscopic deformations are predicted to be larger than the molecular deformations in both the machine and hoop directions due to viscoelastic effects, as expected. An important feature of the model is its ability to predict the locked-in stresses and microstructure, which are related to final film properties.
Polyethylene films prepared from a range of m- LLDPE, LLDPE and ULDPE resins containing 0 and 8% PIB, were manufactured using a Killion cast film extrusion system. FTIR, DSC and mechanical analysis techniques were used to investigate the effect of co-monomer type, density and MFI on the mechanical performance, orientation and crystallinity of these films. The study established that co-monomer type and MFI were the greatest factors influencing mechanical performance and crystallinity. Crystallinity was found to be the most influential factor governing PIB migration in these films and this in turn was related to polymer type, density and MFI.
The influence of the die gap (DG), the blow up ratio (BUR) and the frost line height (FLH) over shrinkability of LDPE and LLDPE films, and on the optical properties of LLDPE was evaluated using a 23 full factorial plan. For LDPE and LLDPE, shrink decreases in the extrusion direction and increases in the transverse direction when BUR increases. The die gap and the frost line height do not affect the shrinkability of LLDPE. Regarding LLDPE films optical properties, the haze decreases and the gloss increases when both, the FLH and the BUR, decrease.
In this paper the use of Neural Networks for the on-line prediction of cure cycle performance is presented. The need of an on-line fast tool for the prediction of the cure cycle characteristics according to real time measurements of the cure process is apparent for the whole polymer composite industry. Various Neural Network architectures and set-ups are presented, discussed and tested to provide the fastest and more reliable solution. The training of the Neural Networks is performed using a 1-D simulation tool. Finally, some ideas about the implementation of this tool in the on-line control of the cure process are presented.
Ultrasonic velocity measurements have been made during cure of DCPD. This material is under investigation for use in reactive rotational moulding in which the moulded part is manufactured using liquid DCPD and a layering technique. Each layer must be sufficiently cured to support the weight of subsequent layer addition. Ultrasound is being explored as a non-intrusive process-monitoring tool to detect mechanical property changes during early cure and enable use of the layering technique. Velocity is observed to decrease, simultaneous with temperature rise. Velocity is then observed to increase as cure progresses. The technique can distinguish variations in rate of cure.
Development of a wireless pressure sensor is motivated to reduce instrumentation and mold modification cost, improve lifecycle robustness, and thereby facilitate the widespread use of in-process sensing for process monitoring and control. In the presented design, the dynamic pressure in the mold cavity compresses a stack of piezoelectric rings, which generate a proportional electrical charge. Using an oscillator-based threshold switching device, the collected charge is relayed to an ultrasonic transmitter, which sends an acoustic signal at specific center frequencies to a receiver outside of the mold. Such a mechanical-electrical transduction process enables the online measurement of mold cavity pressure in a wireless fashion, without any external power supply.
This research investigates the application of ultrasound for monitoring conditions inside microcavities too small to be sensed using conventional sensors. An ultrasonic transducer was installed on an injection mold containing micro-cavities such that the sound pulse would strike the surface of the mold cavity and reflect back to the transducer. Changes in the intensity of reflected echoes are shown to be sensitive to the presence of polymer in the mold. By monitoring this changing reflected echo a signal is produced that is sensitive to conditions in the mold during processing. Two distinct advantages of the sensor are first, that it can sense conditions inside a micro-cavity, and second, that it can potentially do this from the outside of the mold plate, allowing an installation that requires no machining of the mold.
Control of melt temperature in molding of high-precision components depends on the non-linear heat transfer and fluid dynamics behavior governing the process. Such systems are difficult to represent in a standard control strategy, especially if the material changes or set-point profiles are modified frequently in the process. This paper presents a strategy for combining computational-fluid-dynamics (CFD) with active process control to optimize controller performance. In this case the strategy is applied to control simulations of melt temperature in injection molding.
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