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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Influence of Thermal History and Molecular Weight on the Mechanical Properties of High Density Polyethylene
Several variables affect the plastics solidification process, being the thermal history given to the polymer and its molecular weight the more important. Therefore, this paper is mainly aimed at establishing a relationship between thermal history, mechanical properties and molecular weight of HDPE based on mathematical models of the following type: mechanical property =f(molecular weight, crystallinity) through a multivariable non-linear regression method and three-dimensional views of the surfaces generated by the mathematical expressions were obtained to have a better view of the results and models developed, concluding that these models are very useful for the industry.
The Use of Thermomechanical Indices to Establish Straightforward Processing-Mechanical Properties Relationships
The thermomechanical environment imposed to the melt in injection molding is quantified by two thermomechanical indices estimated from computer simulations of the mould filling. These indices are associated to the onset conditions of the microstructure development, and aim at interpreting its final state. As the microstructure determines the mechanical properties, straightforward relationships between those and the thermomechanical indices can be obtained. In this work, axisymmetric specimens were injection molded with systematic variations on the melt and mold temperatures and the flow rate. The mechanical properties were assessed in tensile tests at cross-head velocities of 2, 10, 500 mm/min and 3 m/s. They were related to the thermomechanical indices. Their variations were interpreted in terms of the expectable microstructure of the moldings.
Rubbing Mechanisms of Polymers on Metal Surface Relevant to Extrusion
The processing behavior of a polymer inside an extruder largely depends on the rubbing mechanism of the polymer on the metal surfaces of the barrel and the screw. The rubbing mechanisms of five commercial polymers were investigated from a metal temperature below the thermodynamic melting (or glass transition) range of each polymer to a metal temperature well above the melting range. The rubbing mechanism was found to depend on the polymer properties and the metal temperature. For rigid, amorphous or highly crystalline polymers, the rubbing mechanism is friction" at low metal temperatures below the melting range and "melting" at high metal temperatures above the melting range. For soft crystalline polymers with a broad melting range the rubbing mechanism is complex exhibiting "friction" "tearing" and "melting" as the metal temperature is increased."
Through-Transmission Infrared Welding (TTIR) of Teflon TFE (PTFE)
Through-transmission infrared (TTIR) welding of Teflon®TFE using a Teflon®PFA interlayer was demonstrated to be a well-controlled process that resulted in strong joints. The interlayer was formulated with low levels of carbon black to increase its absorption of the infrared radiation. Designed experiments were used to provide some understanding of important factors.
Methods for Making Nearly Invisible Welded Joints in Clear Polymers
Several ways are described to produce very nearly invisible joints in two transparent polymers. Particles of optically opaque materials can be embedded or deposited on the surfaces of clear acrylic or other polymers through grit blasting, printing processes, use of very lightly colored inter-layers, or spraying/ink deposition. High weld energies such as are found in YAG lasers or xenon heating systems are very capable of producing nearly invisible joints. Light colors other than clear can be welded in this manner as well.
Influence of Mica and Talc Fillers on the Properties of Rotationally Moulded LLDPE
This paper describes the results from an investigation of the effects of talc and mica on the properties of rotationally moulded Linear Low Density Polyethylene (LLDPE). This work concentrates on the effects of the particle sizes and the types of coupling agent. Results show that introducing finer grades of talc and mica improves the impact strength. It has also been found that a maleic anhydride modified polyethylene can achieve better overall properties than a titanate-coupling agent.
Real-Time Dielectric Measurements during Extrusion of Filled Polymers
Mineral fillers are added to polymers to extend and modify physical properties, and their concentrations should be carefully controlled to obtain the desired end-use properties. To achieve this control, real-time measurements are very useful. Previous work has shown that in-line dielectric sensors can measure the concentrations of fillers in non-polar polymers. This work extends the measurements to polar polymers.
Investigation of Crystalline Structure and Orientation of Polyamide 612 in Double Bubble Tubular Film Blowing Process
Uni- or biaxially oriented polyamide 612 (=PA612) films were produced by a double bubble tubular film blowing process at a high extrusion temperature and with a rapid cooling of the first bubble films. The double bubble films stretched in a rubbery state were characterized using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXS), small angle X-ray scattering (SAXS) and infrared (IR) spectroscopy. Biaxial orientation factors were computed with pole figure data and plotted in a White-Spruiell orientation triangle. DSC measurements showed that first bubble films exhibited a spontaneous increase in glass transition temperature (Tg), cold crystallization temperature (Tc) and crystallinity during aging at room condition (22 °C and 32 %RH). Highly biaxially stretched films had a well defined triclinic crystals when they are annealed in a boiling 20% formic acid solution or stretched at a high temperature. Structural parameters of crystals exhibited a big change with stretching conditions.
Structure Development in Biaxial Stretching of Cast Polyamide 11
The development of crystallinity and polymer chain orientation in the biaxial stretching process of cast polyamide 11 (PA11) films was investigated. The characterization of the stretched films was done with birefringence measurements, wide angle X-ray diffraction (WAXS), differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS). Biaxial orientation factors were represented in a White-Spruiell orientation isosceles triangle. As distinct from polyamide 6 (PA6) and polyamide 612 (PA612), DSC scanning of as-cast PA11 film were crystalline and exhibited a little change in crystallinity by aging at room condition. The glass transition temperature (Tg) increased during aging. PA11 highly biaxially stretched in an elevated temperature had monoclinic and triclinic crystals, respectively. The dimensions of the crystals were changed with the stretching conditions.
Block Copolymers as Templates for Functional Materials
There are applications and devices which require controlled distribution of material functionality (electrical, optical, catalytic, magnetic) in two or three dimensions. At the nanometer length scale, attempts to meet this challenge have included template-mediated materials chemistry (Martin 1994) in which track-etched membranes, porous alumina and zeolites serve as the nanoscale reaction vessels for the synthesis of the functional materials. The ability to control both the length scale and the spatial organization of block copolymer morphologies makes these materials particularly attractive candidates for use as templates in the synthesis of functional nanocomposites. Appropriate choices of the repeat units of the block sequences renders them capable of selectivity sequestering preformed inorganic nanoclusters or selectively solubilizing inorganic reagents for in-situ cluster synthesis. Methods exist to produce nanoscale voids which percolate through the structure, leading to processes which coat or backfill the channels with functional materials. Electroless plating methodologies which have been used to apply surface of metals to polymer films can be adopted to produce metallic structures selectivity within block copolymer domains.
Tensile Properties of Linear Low Density Polyethylene (LLDPE) Blown Films
Various LLDPE resins that encompass those polymerized using Ziegler-Natta, metallocene and chromium oxide based catalysts were blown into film and their tensile properties were investigated in relation to molecular orientation. The direction-dependent (MD vs. TD) tensile properties were observed to be significantly different from those of isotropic polyethylene specimens of comparable density. These were explained in terms of orientation and lamellar organization features. Excellent correlation between Elmendorf tear and tensile yield characteristics added credibility to previous hypotheses that specimen stretching and its associated microstructural deformations plays a significant role in Elmendorf tear tests.
Blends of Metallocene Polyethylenes for Recycling of Xerographic Toners
This paper presents experimental results on the blends of metallocene polyethylenes (mPE) for recycling of xerographic toners by reactive extrusion. The experiments were carried out in a reactive twin screw extruder. The evaluation of the mechanical properties and morphology for different blend consist of black xerographic toners with mPE with and without compatibilization by reactive processing. It is rather surprised that the impact strength property is synergistic behavior. The impact strength and the modulus of elasticity of the blends using compatibilizer can be significantly improved. Morphology studies employed scanning electron microscopy (SEM) show that not only the domain size of the phase of black toner can be reduced but also the interfacial adhesion can be enhanced by proper compatibilizeation. Phase morphology and domain size indicate that efficient dispersion was obtained for the compatibilized system whereas the phase of black toner was agglomerated in the interfaces without compatibilization.
Integrating Thin-Wall Molder's Needs into Polymer Manufacturing: Part II
Polyethylene (PE) injection molded rigid containers are widely used for food packaging and promotional drink cups. Molders of these containers have well-defined processing needs and molded part requirements. Likewise, the polymer manufacturer has well-defined manufacturing and analytical methods for characterizing resin properties. This paper presents a predictive model that was developed from molded part testing versus PE resin physical properties. Utilizing this information, the resin producer and the injection molder can work together to improve molded part performance.
Drying: A Closer Look
This paper will discuss the adverse effect on viscosity when polymers are excessively dried. Many processors are concerned exclusively with excessive moisture and give little consideration to the permanent detrimental effects from over-drying. As part size gets smaller in many applications, dryer throughput is lower. The result is extended exposure to the drying process. Thus, the viscosity of the material is increased and permanent loss of material properties occurs. This effect was observed as an actual manufacturing problem.
Blends of Poly(ethene-co-octene) Elastomers
Blends of polystyrene (PS), and polymethyl methacrylate (PMMA) with poly(ethene-co-octene) elastomer (POE) were investigated. The experiments were performed in a counter-rotating reactive twin screw extruder. The evaluation of mechanical properties and morphology were completed to determine stress-strain behavior, impact, domain size, and interfacial adhesion for the blends. The results of tensile strength, modulus of elasticity, and impact properties for the blends show that incompatible and synergistic behavior over a wide range. Morphology studies using scanning electron microscopy (SEM) indicate that the domain sizes of rubber phase in the blends are rang from 1 to 15 ?m and a variety of interfacial adhesion behavior. All the blends displayed phase-separated. The blends of polystyrene / poly(ethene-co-octene) elastomer with compatibilization illustrate that not only the domain size of the phase of elastomer can be reduced but also the interfacial adhesion can be enhanced. The mechanical properties of the blends using compatibilization , such as impact strength and tensile strength, can be improved.
Melt Temperature Considerations for Extrusion
Melt temperature measurement and control are important to understand when optimizing or studying extrusion systems. This extrusion parameter is not as simple to measure as it may seem. This discussion will include the devices that are typically used for the measurement and control of melt temperature and the methods of employing the devices to get meaningful results. Accurately knowing the melt temperature level of a given system allows an accurate comparator for possible improved equipment design. Adjusting melt temperature via altering machine parameters for optimized extrusion results requires that the measured value is a meaningful number. A general discussion of melt temperature in extrusion will be carried out for this tutorial and the measurement and control of this important parameter will be discussed.
Polydiacetelene Fiber Optic Pressure Sensors
Micro-opto-electro-mechanical sensors (MOEMS), where optics are integrated with micro-electro-mechanical systems (MEMS), are logical candidates for sensing flow, temperature and pressure in harsh environments. MOEMS offers small size, high frequency response, immunity to electromagnetic interference, and resistance to degradation from exposure to harsh environments. However, interfacing MEMS with fiber optics is quite challenging. Here we discuss the possibility of coating the fiber with a pressure sensitive polymer (polydiacetelene) to increase its coupling strength to a MEMS' deformable diaphragm. Interestingly, we noticed that the coated fiber, in this case, was itself sensitive to hydrostatic pressure and could be directly used as a pressure sensor. The sensitivity, reproducibility and the structure of this simple and inexpensive structure are discussed in this work.
Fiber-Optic Electric Field Sensors Using Polymer-Dispersed Liquid Crystal Coatings and Evanescent-Field Interactions
A simple evanescent-field fiber- optic electric-field sensor is reported. The sensor is constructed by coating the exposed fiber-optic core with a polymer-dispersed liquid crystal (PDLC). The effective refractive index of the liquid-crystal polymeric coating [poly(methyl methacrylate)(PMMA)/E7] has a large dependence on the direction and the magnitude of an any electric field present. This dependence was large enough to enable simple transmission measurements to detect the presence of an applied electric field. By coating a PDLC film onto the exposed core of the optical fibers, we are able to detect an electric field. The sensors showed good sensitivity and reproducibility and a polarity dependence was observed. The time response of the device is dominated by the RC time constant of the structure rather than the response of the PDLC and is approximately 3 minutes with 15-20 minute relaxation time. Using an electric circuit model of the device we also discuss how these response times can be improved by many orders of magnitude.
The Effect of Molecular Structure on the Extensional Melt Rheology of Conventional and Metallocene Polyethylenes
Extensional melt rheology and processing characteristics of conventional high pressure low density polyethylene (LDPE) and Ziegler-Natta linear low density polyethylenes (LLDPE) are compared with both narrow and broad molecular weight distribution (MWD), long chain branched (LCB) metallocene polyethylenes. The effects of MWD and LCB on the melt behaviour of these different types of polymers will be presented in terms of their dynamic linear viscosities and their strain-hardening behaviour from transient tensile stress growth experiments. Film processability properties will also be discussed.
Fluorescence Based Temperature Measurements and Applications to Real-Time Polymer Processing
Fluorescent dyes doped into polymer resins are used to monitor the true resin temperature during processing. Two examples of real-time process monitoring are presented: first, the effects of shear heating during extrusion are measured and second, the effects of poor temperature control during extrusion are observed.
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