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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Evolution of Surface Free Energy during Thin Film Polymerization of Main-Chain Liquid Crystalline Polymers
By applying thin film polymerization technique and the Lifshitz-van der Waal-Acid-Base theory, we have determined, for the first time, time evolution of contact angle and surface free energy during the polymerization (or molecular weight increase) of liquid crystalline poly(p-oxybenzoate/2,6- oxynaphthoate). Surface free energy components of these main-chain liquid crystalline copolyesters were calculated from contact angle measurements using a Ramé-Hart goniometer and 3 liquids (water, glycerol and diiodomethane). Experimental data suggest that the Lewis-base parameter (?-) of poly(p-oxybenzoate/2,6- oxynaphthoate) decreases rapidly with progress of polymerization, while the Lewis acid parameter (?+) and the Lifshitz-van der Waals parameter (?LW) do not vary significantly.
Examination of Starve-Fed Single Screw Extrusion in Conventional and Barrier Feed Screws
An investigation of starved-fed single screw extrusion was initiated to study its improved mixing capabilities for the compounding of filler. Experiments were carried out in a 63.5 mm single screw extruder, examining the effect of degree of starvation on a conventional and barrier feed screw. Interest was focused on the mixing/melting mechanism of starved-fed solids-conveying as it affects the size and number of filler agglomerates observed in the extrudate. Both screws showed improved mixing quality with increased starvation. Trends in pressure, torque and power efficiency reflected the improvement in mixing.
Developments in High Strength I-PP: Technology Properties, Applications and Markets
In this paper the manufacture of a new family of high melt strength polypropylenes (HMS-PP), its benefits and application in the field of foam extrusion are discussed. A brief introduction into general pathways of influencing melt strength shows that it is the combination of both, a high strength and high drawability of the polymer melt (due to the introduction of some long-chain branches into the polymer structure) which is the main characteristic of these special materials. The rheological behavior is due to a special post polymerization (Daploy) process which introduces long-chain branches into the propylene polymer by comonomer bridging. The presentation of general properties resulting from the modified polymer architecture is followed by the discussion of benefits HMS-PP gives to polymer processing and to final material properties. In particular it is possible to manufacture non-crosslinked and thermoformable PP foams with a density range down to 0,1 g/cm3 and below by foam extrusion processes similar to the known from polyethylene and polystyrene. Main applications are lightweight packaging trays, beakers and containers as well as technical foams for automotive applications such as headliners, door liners, acoustic panels. In summary it is shown that the new family of high melt strength PP is a challenge and chance for PP to improve in existing and to enter into new polymer processing technologies, applications and markets.
Experimental Study of a New Dispersive Mixer
New dispersive mixing technology for extruders and mixing devices (1, 2) is based on creating strong elongational flow to achieve efficient dispersive mixing. These mixers are designed so that all fluid elements pass through the high stress regions several times. One version of the new mixer, CRD-4, was tested on a modular 45 mm extruder using a dryblend of polyethylene and polystyrene. The CRD-4 mixer was tested against a Leroy/Maddock mixer and a Maillefer mixer. The mixing capability was studied by microscopic analysis of the domain sizes of cross sections of extruded strands. The mixer performance was also analyzed with respect to pressure profiles, characteristic curves, and melt temperature distribution. It was found that the CRD-4 mixer achieves a fine level of dispersion under most circumstances. The Leroy/Maddock mixer has limited dispersive mixing capability at low screw speed; however, its dispersive mixing capability is better at high screw speed. The CRD-4 mixer is designed with forward pumping capability. As a result, the output-pressure characteristic of a screw with a 6D CRD-4 mixer is essentially identical to the same screw with the mixer replaced by a conveying section.
The Adjustable Grooved Feed Extruder
Grooved feed extruders have been around since about the 1960s. These extruders offer considerable advantages over conventional extruders, such as higher throughput, better stability, and the ability to process very high molecular weight polymers. There are some important disadvantages as well, for instance, higher motor load, wear is more likely, high pressures in the grooved region, and the screw design has to be adapted. The disadvantages of the grooved feed extruder disappear when the grooved feed extruder is made with a mechanism that allows adjustment of the groove depth. This paper will report on the development of grooved feed extruders that incorporate an adjustment mechanism that allows the depth of the grooves to be changed, during actual operation, from zero to full depth. Operational data from actual extrusion experiments are presented.
Use of Stereolithography for Extrusion Dies
Stereolithography has been used for many years to develop prototype parts. This is a good method for evaluating preliminary designs, but restricts the fabrication material to that used in the stereolithography equipment. It is more desirable to produce molds using stereolithography and prepare parts in the material of choice. This method has been successfully used for injection molding, but has not been evaluated for use in extrusion. This work examined the use of die inserts made by stereolithography for profile extrusion. An existing die was modified to allow epoxy inserts to be placed in the die so that the dimensions of the profile could be modified quickly without preparing a new metal die, but rather changing to a new epoxy die insert. This technique allows new profiles to be rapidly evaluated. In this work the lifetime of the epoxy inserts was determined for varying profile cross-sections. The effect of temperature and pressure on the lifetime of the epoxy die inserts was also measured.
Trade-Offs in Blown Film Processing-Structure-Property Behavior of LLDPE Type Resins from Chromium, Metallocene and Ziegler-Natta Catalysts
Linear low density polyethylene (LLDPE) resins are a very important class of resins for the blown and cast film industry. In this paper, the processing-structure-property behavior and trade-offs observed with three LLDPE resins made from chromium, metallocene and Ziegler-Natta catalysts were examined and critically compared. First, their basic molecular and rheological properties were examined. The blown film performance of these resins was examined with respect to the effects of film thickness and molecular orientation on film properties. The processability of these resins was compared through an examination of the typical extrusion and film blowing parameters. The extensional viscosity behavior of these resins using Cogswell's converging flow analysis was compared. Finally, an attempt was made to highlight the advantages and disadvantages of each resin type as they apply to blown film applications. The overall objective, and hope, of this work was to demonstrate that LLDPE resins from the various catalysts are dramatically different in nature, thereby resulting in different trade-offs with respect to their processing - structure - property behavior in film blowing.
We present methods of calculation of mechanical properties (stress relaxation. creep. dynamic mechanical. tension. etc) of polymers based on the time t temperature T correspondence. The equations are applicable in wide temperature ranges and require relatively small amounts of experimental data. The conventional wisdom says that the correspondence principle is applicable to one-phase materials only: we prove otherwise since successful applications of our formulae include also notoriously multi-phase polymer liquid crystals (PLCs). Our equation for the temperature shift factor is used in conjunction with the Hartmann equation of state (valid for polymer solids as well as for melts). Since the origin of the time temperature correspondence lies in free volume, we explore also methods of free volume variation other than temperature manipulation. In particular. we report progress achieved in using the time t stress ? correspondence principle.
Ranking of Correction Methods - How Effective Are They?
Capillary rheometry is the most popular rheological measurement technique for polymer melt characterization. One of the reasons it is used so frequently is the system's simplicity compared with a rotational rheometer. However, the analysis and interpretation of the raw experimental data (pressure drop as a function of piston velocity) can be time consuming, before the viscosity function can be determined in absolute terms. The Bagley-Correction to determine the entrance pressure losses and the Rabinowitsch-Weissenberg-Correction to determine the true shear rate at the wall (caused by the difference between Non-Newtonian flow and Newtonian flow), are the two classic methods for the determination of the true viscosity function. The failure of adhesion of the polymer melt at the capillary wall, encountered as slippage, asks also for correction. Viscous heating due to dissipation can be significant for high molecular weight polymers processed at high shear rates and asks also for a correction of the viscosity function. The correction methods mentioned will be analyzed with respect to their influence on the viscosity function. It is a goal of this work to provide a quantitative ranking of the methods in question for selected polymers.
Pressure Shear Pulverization (PSP) Process for Thermoplastic and Thermoset Waste
A novel process of pulverization known as Pressure Shear Pulverization (PSP) process has been developed for thermoplastics (PE, PP, PS, PVC, PA, PET and/or their mixtures), thermosets (polyurethanes and phenolics), composites, and various blends (thermoplastics and paper). PSP is a proprietary, non-extrusion process and is realized inside a specially designed pulverization head. It is very different from cryogenic grinding, various versions of solid state shear extrusion (SSSE), and other size reduction processes. PSP has several advantages, namely, high output, low specific energy consumption, and low cost of pulverization head. PSP process is capable of producing coarse to very fine particles by manipulating the processing parameters. This paper deals with the development of pulverization of pre-consumer cross-linked LDPE foam waste and LDPE/Paper mixture by PSP process. As a model system, the processibility and properties of virgin LDPE have been studied. Physical properties of LDPE foam waste and polymeric powder have been determined and compared to understand the behavior of polymer under the combined action of thermally and mechanically induced stresses. Lab-scale and pilot-scale PSP machines have been designed and constructed.
Integrated Use of Educational Software for Product/Process Design
As the use of plastics products in numerous areas continues to rise rapidly, a growing number of personnel in companies, as well as students from academic institutions, have a need for efficient and user-friendly educational tools to acquire the basic knowledge necessary to either undertake a conversion to plastics, or start a career in plastics. Plastics products have to be designed and then manufactured. Probably more than with any other material, the geometric design, material selection and manufacturing must be integrated to get good and economical products. This is related to the wide variety of types and grades of plastics, associated with a very wide variety of applications using a wide variety of distinct processing techniques. We have used our long educational experience in academic environments, as well as our extensive involvement with professional/industrial seminars, to develop a series of interactive CBT programs" (Computer-Based Training programs) which address different needs and complement each other. In this presentation we will emphasize the simultaneous use of the various software to quickly acquire knowledge related to several specific plastic products. Since the softwares were designed to be used in either instruction mode (instructor in classroom situation) or in self-study mode (individuals on their own) we will address these two distinct cases. A brief description of major features of four of our Windows-based softwares is first presented in the following."
Single-Site Catalyzed Polyolefin for Fresh-Cut Produce Packaging - A Comparison between Monoextruded Blends and Coextruded Film
Single-site and Metallocene catalyzed polymers, such as polyolefin plastomers (POPs) are unique due to their narrow molecular weight distribution (MWD) and comonomer distribution (CD). These factors can dramatically enhance the properties such as toughness, clarity, sealability and oxygen transmission rate. While linear low-density polyethylene (LLDPE) exhibits excellent physical properties and drawdown capability, the combination of both resins via blending or coextrusion provides a mix of film properties very difficult to achieve with individual components. This study examines the performance of monoextruded blown film made from blends of POP1 (0.9038 gm/cc density) and POP2 (0.8996 gm/cc density) with LLDPE (0.922 gm/cc), versus coextruded film made of POP1 40 % (1.0 mil) / LLDPE 60 % (1.5 mil). In addition, a bimodal resin (0.9175 gm/cc) was also compared with the above materials for the fresh-cut produce packaging application. Both monoextruded and coextruded films can be used for modified atmosphere packaging (MAP) of fresh-cut produce. Coextruded film is the best option for low respiration products because of its excellent sealing performance over other monoextruded films. The end use requirements at the reduced cost are better satisfied by bimodal resin film compared to monoextruded films made of POP1 and POP2 with higher LLDPE contents. Monoextruded blends of POPs with lower LLDPE content (< 40 %w) exhibit most of the property requirements of moderate to high respiration rate fresh-cut produce.
Experimental Studies of Inhomogeneous Post-Yield Deformation in LLDPE Films
Heterogeneous deformation in the form of dilatational bands is observed under certain biaxial stress states which closely resembles uniaxial necking in LLDPE blown films. The formation and orientation of dilatational bands is a function of film morphology and stress state. The dilatational bands form, with their length aligned with the machine direction (MD) of the film, under equibiaxial stress states and nonequibiaxial stress states when the higher principle stress is coincident with the transverse direction (TD). However, homogeneous deformation is observed if the higher principle stress is coincident with the MD. Similarly, uniaxial specimens show necking when the stress is applied in the TD and affine deformation when the stress is applied in the MD. Neck boundary propagation under uniaxial loading is only due to consumption of undrawn material, while dilatational band boundary propagation under an equibiaxial loading also includes simultaneous continued deformation of the drawn material.
Application of Iodine-Doped Poly(p-Phenylene) Langmuir-Blodgett Films as Homogeneous Alignment Layers
Poly(p-phenylene) (PPP) ultra thin films oriented by the Langmuir-Blodgett technique were applied as homogeneous alignment layers and provide some orientation. Poly(2,5-dicarboxyl-1,4-phenelene) (PDCP) and o,o',o'-trihexadecanoyl-triethanolamine (NIII) were used to form the precursor salt, which was transformed into PPP LB films via pyrolysis. A pretilt angle of 0.2° was measured via crystal rotation method on antiparallel liquid crystal cells with PPP LB films as the homogeneous alignment layers. Thermodynamic properties of these Langmuir films at the air-water interface such as their isotherms and creep test were studied. These LB films were characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, electron diffractometry and wide angle X-ray diffractometry. Room-temperature electrical conductivity measurements were performed on the high-temperature iodine-doped PPP LB films via a four-probe method.
Novel Stress/Strain Sensors Based on the Mechanochromic Properties of Liquid Crystalline Polydiacetylenes
Polydiacetylenes obtained from a series of liquid crystalline diacetylene monomers and macromonomers (polymers containing diacetylene groups) exhibit mechanochromic behavior in which their original color changes upon exposure to mechanical force (tensile or shearing). These polymers have been used to develop novel, intrinsic stress/strain sensors based on their mechanochromism. Our study of morphology, crystallographic structure, and optical properties showed that the mechanochromism corresponds to structural phase transitions from crystalline to liquid crystalline phase. This paper will also discuss the relationship between chemical structure, optical properties and mechanical properties of these PDAs.
Aniline Oligomer as a Chemical Sensor
Hexadecamer aniline (16ANi) can be easily dissolved in a mixed solvent of NMP and CHCl3. This mixed solvent allows 16ANi to spread on water and form coherent films. 16ANi multilayer LB-films were successfully deposited on different substrates (e.g. glass, silicon and germanium) with the aid of 22-tricosenoic acid (TA). Uniform films from Y-type deposition were obtained as confirmed by x-ray diffraction and UV-vis spectroscopy. The thickness of each layer is about 29 Å. Mixed films of 16ANi-TA have the same optical properties as polyaniline. The films have been utilized as chemical sensors through measured changes in electrical conductivity.
Applications of FTIR Spectroscopy to Characterize Polymers Processed with Supercritical Carbon Dioxide
Supercritical CO2 can induce crystallization of amorphous polymers. Molecular level insight into the microstructures of CO2-processed polymers is needed to form a basis for utilization and optimization of supercritical fluid processing of polymeric materials. FT-IR spectroscopy has been applied to elucidate the morphology and microstructure of polymers processed with supercritical CO2. FTIR spectra of syndiotactic polystyrene show an increased degree of crystallinity after being subjected to scCO2. The various crystalline forms induced by CO2 in syndiotactic polystyrene were characterized via FTIR spectra. FTIR spectroscopy has been also used to measure the kinetics of CO2-induced crystallization in these polymers.
Thermoplastic Composites Containing Deformable Reinforcing Composites
The forming and shaping of thermoplastic composite prepregs is severely hindered by the lack of deformability of the reinforcing component (e.g. glass or carbon fiber) and the separation of the matrix from the reinforcing component. In this paper we study the behavior of thermoplastics reinforced with two types of reinforcing components which are deformable in subsequent shaping operations. In particular we investigate the formability of thermoplastics (e.g. polypropylene, polyetherimide, and polyphenylene sulfide) reinforced with thermotropic liquid crystalline polymer (TLCP) micro-fibrils of higher melting point than the matrix and with melt processable glass. Studies include thermoforming, stretching, and compression molding of blanks containing micro-fibrils of both reinforcing materials.
A Method to Quantify the Average Biaxial Orientation of the Crystalline Phase in Polyethylene Blown Films
Following an approach suggested by Kissin (Journal of Polymer Science: Polymer Physics Edition, v30, 1165, 1992), a general form of the Beer-Lambert law was employed to quantify the White-Spruiell biaxial orientation factors for various polyethylene (PE) blown films using IR absorption data at 719 cm-1 and 730 cm-1. It was pointed out that certain assumptions employed by Kissin are invalid for most polyethylene blown films. However, when alternate assumptions based on sound experimental evidence were employed, the resulting orientation estimates were in good qualitative agreement with X-ray diffraction patterns for various low and high density polyethylene blown films.
The Relative Influences of Process and Resin Time-Scales on the MD Tear Strength of Polyethylene Blown Films
This paper is concerned with the effects of polymer relaxation time (as estimated via melt rheology) and process extension rate (as quantified via an average MD extension rate at the frost line) on the MD tear strength of various polyethylene blown films. An increase in melt relaxation time at constant process conditions or an increase in process extension rate for a given resin (constant melt relaxation time) were both observed to result in lower blown film MD tear strength. These observations were interpreted in terms of molecular orientation and deformation mechanisms in polyethylene, with preliminary data suggesting that interlamellar shear plays an important role in determining the MD tear performance of LDLPE and LLDPE blown films.
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