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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Effect of Crystalline Structure on Tear Resistance of LDPE and LLDPE Blown Films
Low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) blown films differ significantly in the ratio between machine and transverse direction tear resistance. In this paper, the relation between crystalline morphology and these differences in film tear anisotropy was investigated. The crystalline morphology and its orientation were probed using microscopy and infrared spectroscopy. Significant differences in crystalline morphology were found: LDPE develops a row-nucleated structure, while a spherulitic-like superstructure was observed for LLDPE. These structural differences were shown to translate into different ratios of machine and transverse directions tear strengths.
Effect of Processing Parameters on Properties of LLDPE-Based Mono- and Multilayered Blown Films
In this paper we investigated the effect of processing parameters on end-use mechanical properties of monolayer and 5-layer coextruded polyethylene blown films using three different linear low density (LLDPE) polyethylene resins. The three investigated LLDPEs were: a conventional Ziegler-Natta gas phase ethylene-butene copolymer, and two solution ethylene-octene resins produced with Ziegler-Natta and single site catalysts. The octene copolymers were produced using NOVA Chemicals advanced SCLAIRTECH™ process and catalyst technologies.It was found that tear strength increases in the direction perpendicular to the highest orientation, that impact and puncture strength increase with the overall orientation and finally that the effect of orientation due to shear stresses in the die on final film properties is not significant due to rapid macromolecular relaxation before crystallization.
A Predictive Model for Dart Impact Strengths of Solution Octene LLDPE Film Resins
A predictive dart model has been developed for solution ethylene/octene linear low density polyethylene (LLDPE) resins produced using a high activity Ziegler- Natta catalyst and NOVA Chemicals’ Advanced SCLAIRTECH technology. By incorporating both polymer properties and blown film processing variables, a robust model was developed through multivariate statistical analysis. The model suggests that dart impact is a nonlinear function of polymer structure, machine direction strain rate and a corrected Deborah number. This model has also demonstrated its utility in product development at both pilot and commercial scales.
Control of Blown Film Tear Strength Anisotropy through Blending of LDPE and LLDPE
Low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) blown films differ greatly in tear strength anisotropy as LDPE generally exhibits MD>>TD tear resistance while LLDPE shows greater TD tear resistance values. In this paper, we examine the role of LLDPE/LDPE blend compositions on tear strength anisotropy and on the crystalline morphology developed during the blown film process. The crystalline morphology and orientation were measured using microscopy and infrared spectroscopy. Blending of LDPE into LLDPE suppressed the development of superstructure of LLDPE. Infrared studies suggested that both the a- and c-axes are oriented towards MD for high LDPE concentration blends. c-axis orientation gradually shifts from MD to the perpendicular plane as LDPE content decreases, accompanied with an increase of a-axis orientation in MD. Correlation between the tear resistance and the crystalline lamellae orientation is discussed.
LLDPE Blown Films Property Enhancement through Coextrusion
In this paper we investigated the performance of multilayer co-extruded LLDPE blown films. We compared five-layer films with monolayer dry-blended films and highlighted the effect of layer composition and layout on the end-use properties of the co-extruded films. Three different LLDPEs were used: a conventional Ziegler-Natta LLDPE gas phase butene copolymer, an advanced Ziegler-Natta LLDPE solution octene copolymer and a single site LLDPE solution octene copolymer. Numerous five-layer co-extruded structures comprising the single site resin and the other two Ziegler- Natta resins were produced. The coextruded structures composed of the LLDPE butene and the single site resin offer improved tear performance, relative to monolayer blended films; this was assumed due to the presence of interfacial transcrystalline layers. Also, blends of the single site LLDPE and the advanced Ziegler-Natta LLDPE octene resins within selected layers of coextruded films showed slightly enhanced tear resistance. Finally, it was found that haze is significantly reduced when the outside layers are composed of the single site resin. IntroductionA large proportion of the Linear Low Density Polyethylene (LLDPE) production is processed into thin films through the film blowing process and used as flexible packaging. An increasing number of PE film producers are equipped with multilayer blown film lines which offers more flexibility in product design and cost reduction. Consequently, it is not surprising to find in the literature several papers exploring the advantages of coextruded structures [1-4].In this work, we first compare the end-use properties of LLDPE-based coextruded blown films with monolayer blended films and then investigate the effect of layer composition and layout on film performance.
Extrusion Foaming of TPVs Using Water-Filled Polymers
A novel, physical foaming agent, ‘water filled polymer,’ has been proven successful in producing low density foamed TPV profiles on standard single screw extruders. Extrusion processing parameters and physical properties (cell size, cell shape, tensile properties, specific gravity, compression load deflection, compression set, surface smoothness and water absorption) of TPV foamed profiles are reviewed. These results are compared to results from other types and forms of foaming agents used to produce foamed TPV profiles.
Orientation and Property Correlation on LLDPE Blown Films
The orientation and property correlation of polyethylene (PE) blown films has been studied. A LLDPE polymer (DOWLEX* 2045A) was used to fabricate films at different conditions with blow up ratio, die gap, and frost line height as the variables. The White-Spruiell orientation factors of crystal unit cells, amorphous chains, and lamellae were determined from wide-angle X-ray diffraction pole figure, birefringence, and SAXS. It was found that Keller-Machin type 1 row structure exists in these LLDPE blown films. A correlation between the orientation of each element of the morphology hierarchy has been revealed. Key mechanical properties including Elmendorf tear, dart impact, and tensile strength in both MD and TD have been determined. These properties have been correlated to the orientation. These correlations have been linked to underlying morphology and microdeformation mechanisms.
Enhancement of Poly (L-Lactide) Properties through Nanocomposite Formation
Nanocomposites are materials that exhibit a change in composition and structure over a nanometer length scale. In many cases, these systems have shown remarkable property enhancements compared to traditional polymers. Recently, poly (L-lactide) (PLLA) has received considerable attention because of its “green” nature. However, the end-use properties of this biodegradable polymer typically fall short of typical petroleum based polymers. Therefore, PLLA/montmorrilonite nanocomposites have been prepared via solution blending in an attempt to enhance the properties of PLLA.
Mechanisms of Clay Exfoliation in a Polymer Matrix during an Extrusion Process: A Structure-Property Relationship
Polymer-organoclay nanocomposites were prepared by melt extrusion techniques, employing different processing conditions and material formulations. The structure-morphology relationship of the nanocomposites was analysed using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD). Results from the rheological study showed significant correlation between the dynamic rheology of the polymer melt during the extrusion process, and the exfoliation mechanism of the organoclay layered-silicate observed in the WAXD diffractogram and TEM analysis. Results also indicate that the exfoliation process in the extrusion environment could be achieved through different mechanisms and these mechanisms can be optimised by adoption of different extrusion processing conditions and material formulations.
A Study on Intercalation and Exfoliation of Layered Silicate Nanoparticles in Thermoplastic Polyurethanes
Thermoplastic polyurethanes serve as an attractive system for the study of intercalation and exfoliation of layered silicate nanoparticles. The clay galleries are easily intercalated by low molecular weight diisocyanates, polyols, and butanediol before carrying out condensation polymerization. A majority of existing studies reported intercalation and subsequent polymerization in solutions and obtained fully exfoliated clay structures, although industrial implementation of such technology requires development of bulk polymerization schemes.In this study, we utilized the unreacted isocyanate groups in the chains of prepolymer and chain extended polymers to tether nanoclay particles and studied the properties of the resultant materials produced by sequential addition of organically treated silicate particles into prepolymer and to the fully formed polymer chains. As high as 216% increase in tensile strength and 87 % increase in elongation at break were observed with 1-2 wt% organically treated clay particles.
Introducing a New Miniature Mixer for Specialty Polymer Blends and Nanoscale Composites
A new miniature mixer for polymer blends and nanocomposites has been designed. This mixer uses a single, asymmetric rotor spinning within a cylindrical cavity, for elongational and high-shear mixing. The mixer was evaluated by comparing its performance with an internal mixer and a MiniMAX molder. Both immiscible polymer blends and vapor grown carbon fiber (VGCF) composites were prepared using several mixers, and their morphology was studied. The new mixer was generally found to create a well-dispersed and uniform morphology, with results comparable to those of an internal mixer.
Preparation and Mechanical Property of Synthetic Zirconium Phosphate-Epoxy Nanocomposites
The morphology and mechanical property of synthetic zirconium phosphate (ZrP) - epoxy nanocomposites were studied. The nanocomposites were characterized using wide angle X-ray scattering and transmission electron microscopy to confirm the exfoliation of the ZrP layer structure in epoxy matrix. The mechanical property and fracture toughness (KIC) of ZrPepoxy nanocomposites were studied using dynamic mechanical analysis, tensile tests, and single-edge-notch three-point-bend test methods. The rubbery plateau modulus of the surface modified ZrP-epoxy nanocomposite (M-ZrPNeat) is found to be about 4.5 times higher than that of the reference epoxy. The tensile modulus of the M-ZrP-Neat nanocomposite is increased by 50% with only 1.9 vol% of ZrP addition. However, the elongation at break was decreased drastically.
Mechanism of Exfoliation of Nanoclay Particles in Epoxy-Clay Nanocomposites
In this study, a rheological interpretation of exfoliation of clay particles was proposed using experimental observations in the curing of organically treated nanoclay- Epon828 mixtures with three curing agents. The elastic force exerted by cross-linked epoxy molecules inside the clay galleries was found responsible for exfoliation of clay layers from the intercalated tactoids. Complete exfoliation of clay galleries was observed under the conditions of slow increase of complex viscosity and fast rise of storage modulus. Gel time presented an upper bound of time available for exfoliation. Faster intra-gallery polymerization, although expedited clay exfoliation, was found to be not a necessary condition.
Epoxy-Aided Dispersion of Nanoclay in PMMA
The dispersion of organically treated nanoclay particles in thermoplastic polymers using thermosetting epoxies was investigated using polymethylmethacrylate (PMMA) and a mixture of aromatic and aliphatic epoxies. The values of tensile and impact strengths of the resultant composites were compared with PMMA-clay, epoxy-clay, and PMMA-epoxy composite systems. It was found by wide-angle-x-ray diffraction (WAXD) and transmission electron microscopy (TEM) that epoxy helped produce exfoliated clay structures, although the exfoliated clay particles remained inside phase separated domains of epoxy of ~1?m in diameter. Nevertheless, tensile and impact strength improved by respectively 40% and 25% for clay loading of 2wt% over both PMMA and PMMA with 2wt% clay.
Enhanced Failure Properties in Layered Silicate Nanocomposites Formed by Melt Processing I. Polyoxymethylene as a Model Matrix Material
Polymer / layered silicate nanocomposites have been extensively studied over the past decade as promising high performance materials. Noteworthy mechanical performance, however, would require significant improvement in strength as well as modulus over conventional composites or unfilled polymers. Our objectives extend current research based on existing models to focus on the synthesis of an idealized layered silicate nanocomposite and develop a rationale for the current limitations of intercalation and exfoliation technology in enhancing failure properties. As a first step in this process layered silicate nanocomposites have been prepared by combining polyoxymethylene (POM), an engineering thermoplastic chosen as a model polymer system for its potentially interactive oxygenated backbone structure, with clays having different types of surface treatments. Characterization of the synthesized nanocomposites is accomplished through a combination of X-ray diffraction, TGA, mechanical properties and rheology.
Properties and Structure of LLDPE/HDPE 3-Layer Coextruded Blown Films with Blended Middle Layers
Linear Low polyethylene (LLDPE) and High Density Polyethylene (HDPE) films are largely used in the packaging industry. LLDPE films present excellent impact and tear strengths. By contrast, HDPE resins give rise to stiffer films with good tensile properties but poor impact and tear resistances. This study deals with coextruded blown films containing middle layers composed of LLDPE/HDPE blends. Mechanical properties namely, tear resistance, impact strength and modulus are discussed as a function of HDPE content in the central layers. Melting and crystallization phenomena are explored over a broad range of composition by means of differential scanning calorimetry (DSC).
Biaxial Orientation in Polyethylene Films: Comparison of Infrared Spectroscopy and X-Ray Techniques
In this study, blown low density polyethylene (LDPE) films were produced under different processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous and global orientation factors using birefringence, Fourier Transform Infrared Spectroscopy (FTIR) with a tilted incidence technique and X-ray pole figures. It is well established that FTIR can measure crystalline axes orientation for polyethylenes, as well as the orientation of the amorphous phase. On the other hand, X-ray pole figures determines the orientation of the crystalline axes, and in combination with birefringence can yield the amorphous phase orientation. The results from those techniques are compared and discussed in terms of the accuracy of the techniques and the contributions of different specific entities in FTIR measurements.
Effect of Extrusion Die Geometry on Molecular Orientation of Unfilled Polyethylene
The effect of die geometry on molecular orientation of unfilled polyethylene has been investigated. Four dies with similar exit geometry but having a combination of two different entry angles and two land lengths have been used with a 63.5mm diameter single screw extruder. Extrudate samples were collected using a haul-off rate equivalent to the calculated die exit velocity, to prevent post-die deformation. A range of haul-off rates was also imposed. Orientation was inferred from reversion tests. Land length was found to have the greatest influence on extrudate orientation, but effects due to entry angle were also observed.
Permeability and Mechanical Performance of 3-Layer EVOH/LLDPE Barrier Films with Blended Middle-Layers
EVOH Barrier films are typically 5-layer films comprising a central EVOH layer, tie layers and external polyethylene layers. In this paper, the barrier and mechanical properties of three-layer barrier films were investigated. As a possible mean to increase layer adhesion, the core EVOH layer was blended with linear low density polyethylene over a broad composition range. The tear strength, impact resistance, tensile properties and oxygen permeability were measured as a function of EVOH content. Good oxygen barrier properties were found for LLDPE concentration below 50%. The balance between interfacial adhesion, mechanical properties and oxygen permeability over the possible range of composition for central layer is discussed.
The Mechanical Properties and Crystallization Behaviour of Pigmented Propylene-Ethylene Random Copolymer
Samples of a commercial propylene-ethylene random copolymer containing 0% to 8% phthalocyanine blue pigment were injection moulded using mould temperatures 40°C to 80°C. Thermal analysis (DSC and DMTA) performed on all the samples show the presence of two distinct crystalline phases. The relative predominance of each phase was affected by the mould temperature and the nucleating effect of the phthalocyanine pigment. This binary phase morphology was shown to have a significant effect on the mechanical performance of the polymer, with great reductions in impact performance being recorded for pigmented samples.
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