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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The Effect of Polyethylene Catalyst Type and Pigment Concentration on Crystal Growth during Rotomoulding
This work studied the effect of catalyst type and pigment concentration on the impact properties, crystallinity and morphology of rotationally moulded polyethylene (PE) parts. Microscopy, shrinkage and differential scanning calorimetry analysis techniques were used. It was observed that the base PE catalyst had an effect on the extent of crystallinity but that the level of pigmentation had only limited effect on the extent of crystallinity. The reduction in impact performance for turboblended pigmented samples was due to the relatively poor distributive and dispersive mixing of the pigment within the polymer matrix.
Structural and Thermal Aspects of the Performance of Hybrid Moulds with SLS
Hybrid moulds with molding blocks obtained by rapid tooling techniques are used for production of small batches. The mechanical and thermal performance of the inserts is particularly important at the design stage. This paper describes the use of Selective Laser Sintering (SLS) inserts for hybridmoulds. These inserts were experimentally study and the feasibility of this technology for the fabrication of hybrid-moulds investigated. Computer simulations using commercial software were also carried out. The obtained results show a good agreement between simulation and experimental data.
Analysis of Powder and Pellet Melting during Extrusion with a Perturbation Method
It was reported previously that the melting of a polymer during twin screw extrusion can be quantified using dynamic, on-line monitoring of a perturbation technique. Preliminary results suggested significant differences between the progression of melting of Polypropylene (PP) feed pellets and powders. This paper reports additional data on PP and Polyethylene (HDPE) feeds in the form of pellets, powder and pellet/powder mixtures. In addition to a delay of melting in the case of the powder feed, reductions in power intensity of the melting peak were also observed with the pulse perturbation technique. Unexpected behaviors in the melting of powder/pellet blends are described. The perturbation method is further examined by comparing the pulse energy input profiles with the residence time distribution and steady state power consumption over a range of throughput/screw speed (Q/N) operating conditions.
Characteristics of PP/PS/Clay Nanocomposite Produced by High-Intensity Ultrasonic Process
Polymer-clay nanocomposites of various concentrations were prepared by ultrasonically assisted melt blend process. The ultrasonic blend process using high intensity ultrasonic wave was employed to enhance nano-scale dispersion during melt mixing of polymer blend and organically modified clay. The materials studied were linear polypropylene and polystyrene reinforced with organophilic montmorillonite clay (nanoclay) at 3-5 wt% loadings. The effectiveness of the proposed ultrasonic processing technique on polypropylene matrix nanocomposites was evaluated by XRD, rheological measurements and thermal properties. We expected enhanced breakup of layered silicate bundle and further reduction in the size of dispersed phase with better homogeneity compared to the different immiscible blend pairs.Also, it was expected that generation of macroradicals in polymer mixture can lead to in-situ copolymer formation by their mutual combination, which should be an efficient path to compatibilize immiscible polymer blends and stabilize their phase morphology in the absence of other chemical agents.
A Numerical Study of Scanning Through-Transmission Laser Welding
A numerical model has been developed to simulate the heat conduction during the through-transmission laser welding (TTLW) process. The simulations were performed using the SIMPLER (Semi Implicit Method for Pressure Linked Equations Revised) software. The model was used to calculate the changes in the temperatures at points throughout the heated areas of the parts during the entire welding time. The temperature distributions and peak temperatures generated in the faying surface of welds at same line energy (LE) but different powers and speeds have been predicted and examined. Large temperature differences obtained when keeping LE constant, but doubling both power and speed were calculated and interpreted using this model.
Characterization of the Twin Screw Extrusion Process
In contrast to the well developed field of polymer characterization, the advances of extrusion process characterization lagged far behind. Engineers have to deal with problems such as process scale-up and product quality control primarily by empirical means. Practically no quantitative expressions exist between the operating conditions and the important process parameters such as degree of mixing, intensity of mixing and melting, the nature of polymer melting or plasticization, or energy consumption. We propose along with new supporting data that the parameters introduced previously, ?P/?Q and ?P/?N, that is, energy per unit of additional mass and energy per unit of screw revolution could be used to characterize the melting behavior of a polymer in an intermeshing, co-rotating twin screw extrusion process. The parameters appeared to be independent upon the extrusion rate (Q) and screw speed (N) in the ranges examined (4.5 to 36kg/hr and 100 to 500RPM). We further propose that additional parameters, such as those defining the kinetics of melting, average residence time (for melting and the over all) and residence time distribution obtainable by the pulse perturbation technique may be required in order to sufficiently define a given extrusion process.One can also predict with excellent agreement the observed specific mechanical energy input of extrusion, defined by extrusion power/throughput (P/Q), with simple linear expressions (Eqs. 1 and 2). The parameters c1 (?P/?Q), c2 (?P/?N), and a constant c3, can be determined directly by steady state extrusion experiments without employing pulse or step perturbation methods.
Ultrasonic Plunge Welding of Polypropylene Nonwovens
Polypropylene blown micro fibers with spun bonded cover web made from Polypropylene and polyester fibers were used for the experimental study of the ultrasonic plunge welding of nonwovens. A face centered central composite design of experiment (DOE) with 3 process variables and 3 levels was used to evaluate the effects of vibration amplitude, weld time and weld pressure. In addition to those settings, three different welding profiles were used resulting in forty-five different welding conditions with five specimens welded for each condition. Increasing the welding time generally improved the weld strength until it leveled off. For high welding pressures physical damage was observed around the welding area. Finally increasing the amplitude of vibration resulted in making the welding seam tougher with higher breaking forces.
Constructing Unique Micelle Structures of Charged Block Copolymers via Co-Assembly with Organic Counterions
A variety of fascinating micelle structures have been achieved by the assembly of charged triblock copolymers through the interaction with organic counterions in mixed THF/water solution. Essentially, the formation of toroidal micelles was observed in specific conditions of polymer chain constitution, the chain length of each block, the ratio of THF to water and mixing procedures. Our results showed that final assembled structures can be easily tuned by either varying the chain structure of organic counteirons or changing the ratios of THF to water.
Flash Prevention Due to Skin Solidification
The purpose of this paper is to investigate the role of skin solidification in preventing flash during injection molding of amorphous and semi-crystalline resins. In conventional injection molding, polymer melt is injected into a comparatively cold mold, resulting in the development of a solidified layer. A null hypothesis of this paper is that the development of a solidified layer reduces the exerted clamp tonnage on the machine and may even prevent the formation of flash under high pressures resulting in improved part quality. A set of Design of Experiments was implemented with control factors including barrel temperature, mold coolant temperature, pack pressure and delay time; the characterized responses included part weight, part thickness, and flash length. The results indicated that the addition of a delay time between the injection and packing stages eliminated flashing in this application.
Study of Ultrasonic Welding of HDPE-Based Nanoclay Composites
Clay-based nanocomposites have high modulus, high specific strength, and low permeability. They have become popular in many industries because these material properties can be achieved by the addition of small volume fractions of inexpensive clay particles. Ultrasonic welding of four high density polyethylene nanocomposites with 0 wt%, 3 wt%, 6 wt% and 9 wt% nanoclay was investigated. The effects of weld force, amplitude of vibration, and weld time for energy director joints or weld collapse for shear joints on weld strength were evaluated. Three parameter, three level design of experiments (DOE) were utilized to find near-optimum welding parameters. For the best welding conditions for both energy director and shear joints, increasing the nanoclay content resulted in significantly decreasing weld strength. For energy director joints the decrease in strength with increasing nanoclay content was greater than for the shear joints.
Biomimetic Surface Microstructures and Their Replication to Polymeric Materials
Biomimetic surface structures such as anti-reflective protrusions on the moth eye and self cleaning pillars on the Lotus leaf have a profound influence in the development of technologically important engineering devices and systems. In this study, we prepared microstructured polymer surfaces that mimic the surface patterns on the pronotum and the wing of dung beetles (Phanaeus vindex) using micromolding techniques. The patterned embossing master was fabricated by electroforming the surface of the dung beetle. The electroformed nickel replica was then used to hot emboss on ABS substrates. The replicated polymer surface patterns were found to be comparable with the original surface patterns on the dung beetle.
In-Situ Synthesis of Nanocomposite Systems by Interfacial Polycondensation
In this work, layered silicate- and silica-polyamide 66 nanocomposites are synthesized in-situ by interfacial polycondensation to produce highly dispersed nanocomposite products. The two routes involve either incorporating a highly exfoliated silicate structure from a suspension of silicate platelets in one of the monomer phases or generating a silica hybrid through sol-gel chemistry. Two different approaches in the latter route allow the tetraethoxysilane (TEOS) condensation to occur either simultaneously with or sequentially to the nylon polymerization. Transmission electron and x-ray dispersive scanning microscopy, along with TGA, DSC and FT-IR measurements, are used to monitor and characterize the well dispersed structures produced, which are expected to manifest in enhanced thermo-mechanical properties of the nylon.
Effects of Metallization Coating on Ultrasonic Welding of Abs
Thin metal coating of plastic parts for increased optical reflectivity, improved EMI/RFI shielding, decreased permeability, or for decoration has gained more importance in recent years in automotive, electronics, medical and toy industries. This coating is often found in the weld area and there are concerns regarding its effect on weldability. Therefore, in this work ultrasonic welding of ABS components with metallic coatings was studied to evaluate their effect on weld strength. Two types of coatings were studied: an aluminium coating with hexamethyldisiloxane (HMDSO) as its topcoat and a stainless steel coating. The coated ABS was ultrasonically welded to uncoated ABS. Three factors, weld time, weld pressure, and amplitude of vibration were varied to find near optimum welding conditions. It was found that the aluminum or stainless steel coating had a very small effect on the ultrasonic weld strength for ABS. The maximum weld strength obtained was 28.5 MPa, 28.2 MPa and 26.9 MPa for uncoated, and for aluminum, and stainless steel coated ABS, respectively.
Ultrasonic Assisted Extrusion of HDPE/Clay Nanocomposites
High density polyethylene (HDPE) /clay (Cloisite-20-A) nanocomposites were prepared by using single screw compounding extruder with continuous treatment of ultrasound at different amplitude up to 10?m. The die pressure and power consumption due to ultrasound were measured at different feed rates of materials of various clay concentrations up to 10 wt%. Rheological, mechanical and thermal properties of ultrasonically treated and untreated nanocomposites were studied. X-ray diffraction (XRD) and transmitted electron microscope (TEM) were used to investigate the dispersion of clay and nanocrostructure of composites. The experimental results showed that sonication enhanced the dispersion during melt mixing of HDPE and clay.
Thermal Transitions and Rheology of Propylene-Ethylene-Based Terpolymers
We report on the thermal and the flow characteristics of newly developed propylene-ethylenediene terpolymers. These propylene-rich products were made using single site metallocene catalyst Exxpol™ technology and cover a broad range of chemical composition. The thermal transitions were determined using thermal scanning calorimetry (DSC). The glass transition temperature decreased from about -18 to -28 °C as the ethylene content was increased from 8 to 16 wt%. The crystallinity and the crystallization rate were also strongly affected by the composition. The linear viscoelastic behavior of the different polymers was measured with small amplitude oscillatory shear at various temperatures. The modulus and the viscosity are characteristic of linear polymers and are, for similar molecular weight, independent of chemical composition. The incorporation of un-saturation makes these polymers easily cross-linkable using various chemical or radiation techniques. The crosslinking helps extend their end-use application to elevated temperatures, much higher than their uncrosslinked copolymer counterparts, as demonstrated by dynamic mechanical thermal analysis measurements.
Synthesis of Needle-Like Polyanilines
Needle-like polyanilines (PANi) were prepared in aqueous media by chemical oxidation. P-toluenesulfonic acid (pTSA) used to protonate aniline formed good conditions to make anilinium complexes. By slow addition of ammonium peroxydisulfate (APS), polyanilines were prepared in the micelles and grew to be needle-like aggregates potentially useful as conductive fillers for electromagnetic interference and radar absorbing materials. The needle-like aggregates prepared at 15°C showed conductivity up to 3 S/cm and a maximum aspect ratio of 26 L/D, and were observed to partially peel off into fibrils after washing by means of optical microscopy and scanning electron microscopy (SEM). The needle-like polyaniline-pTSA complexes prepared with 0.5 M aniline concentration showed good thermal stability up to 200°C. The high conductivity of the needle-like aggregates was ascribed to their well developed crystalline structures compared with those of spherical particles.
Manufacturing and Characterization of PET Single-Polymer Composites
A novel approach of using slowly crystallizing polymers to form single-polymer composites (SPCs) was investigated. The approach was demonstrated using poly(ethylene terephthalate) (PET) as a model system, with which distinct physical forms having a large difference in melting temperature can be readily obtained. Using this approach, the process window can be widened to above 70°C and thus the SPC manufacturability is greatly enhanced. The holding time was found to play a profound role in influencing the properties of the SPC. Excellent fiber-matrix interfacial adhesion was obtained at heating temperature 180°C and holding time 10 s. The results also indicated that the heating rate plays a significant role in affecting the fusion and adhesion of the composite. With reduced heating rates, the adhesion properties are rapidly deteriorated.
Effect of Morphology and Particle Size on the Mechanical Properties of San Composites
The effect of morphology (core-shell and three-layer) and particle size on the mechanical properties of a SAN composite was investigated. The core-shell (CS) and three-layer (TL) particles with same global composition (60PBA/40PS) were both obtained by emulsion and microemulsion polymerization to obtain particles with different size.The composites with particles obtained by emulsion, independently of the morphology (CS or TL) and particle size (170 and 220 nm); have at maxima in impact resistance at a 20% of particles content. A different behaviour, however, was observed when particles obtained by microemulsion were used. The composites with TC particles obtained by microemulsion polymerization show a maximum in impact resistance at 10% particles, but impact resistance of composites with CS particles obtained by microemulsion polymerization did not show a maximum and increases with particles content.
The Interactions between TiO2 Surface and Polymer Additives
A common pigment used in many plastics application is titanium dioxide, TiO2. The pigment is a very effective light scattering inorganic oxide for the coloration and protection of plastic articles. Typically, a TiO2 pigment contains a coating on the particle surface that is tailored for plastic applications. For example, for plastics applications that will be exposed to a high degree of outdoor exposure, a coating is placed on the particle surface to mitigate the photo catalytic characteristics of pigmentary TiO2. Additionally, a TiO2 particle coating is used to mitigate the interaction of polymer additives with the TiO2 surface to prevent the formation of chromophores from additive deactivation. This paper proposes a mechanism for chromophore formation for several polymer additives and compares the rate of chromophore formation of various TiO2 materials in a polyethylene matrix.
Precise Curing Analysis of Accelerated Unsaturated Polyester Reactions under Raman Spectroscopy
Raman Spectroscopy has been found to be a novel method for the characterization of thermosetting polymerization reactions. Unsaturated polyester (UP) resin curing reactions were monitored through a half inch quartz lens by Raman scanning at various rates and the results were compared to DSC scans at the same conditions. At optimal parameters where the reaction rate is controlled Raman provides valuable information of the diffusive reaction period as well as of the initial stages of the reaction. From the spectral changes in peak height, the curing process was monitored. Initiators commonly used in pultrusion process where a rapid reaction undergoes were used and it was found that this on-line technique is valuable even in accelerated reaction processes.
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