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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Cracking of Resin Rich Layer Joined to Tank Wall Due to Fluctuating Liquid Level
Composite laminate tanks are used in corrosive services in chemical process plants. The inner surface of tanks usually consist of a glass reinforced layer that is mostly resin and is joined to the tank structure to form a corrosion barrier. A large diameter, open top, composite laminate tank containing a hot brine solution suffered vertical cracking in the corrosion barrier during normal process operations. The process involved relatively rapid changes in the liquid level at different times during each day. Vertical cracks were discovered in the corrosion barrier by plant inspectors during a routine plant turnaround. Finite element modeling was used to demonstrate that the cracking was due to transient thermal stresses near the liquid vapor interface that resulted from the fluctuating liquid level and natural convection from the tank wall in cooler weather. In this research, the effects of the amount of glass reinforcement in the resin rich corrosion barrier were also studied. The outer surface of the tank was insulated, but the insulation does not appear to have been a factor in the cracking.
Rheological Properties of PVC/Wood-Flour Composites
Using a factorial design approach, this study examined the effect of the component materials on the viscoelastic properties of PVC/wood-flour composites. Statistical analysis was performed to determine the effects of wood flour content, acrylic modifier content and plasticizer content on the die swell ratio and viscosity of the composites measured on a conical twin screw extrusion capillary rheometer. The experimental results indicated that both the wood flour content and acrylic modifier content have significant effects on the die swell ratio and viscosity of PVC/wood-flour composites.
Reactive Blends of Poly (Vinyl Chloride) and Thermoplastic Polyurethane
In this study, a novel reactive blending technique was used to produce poly (vinyl chloride) (PVC)/thermoplastic polyurethane (TPU) blends that are otherwise difficult to produce by a conventional melt blending techniques due to degradation at elevated processing temperatures. Morphological and spectral characterization studies revealed that reactive blending process generated better mixing relative to melt blending process. The miscibility of the PVC with the polyols of the TPU and with the TPU was studied by changing in the chemical structure of the polyol.
A Study of the Processing Characteristics and Mechanical Properties of Multiple Recycled Rigid PVC
This study focuses on the ability of U-PVC to be processed a number of times. Three different types of U-PVC were investigated: virgin lead stabilised and virgin calcium/zinc stabilised material and reground, 20 year old, post-consumer windows. Each material was extruded four times and samples taken at each stage for rheological and mechanical analysis.
Fast Joining of Composite Pipes Using UV Curing FRP Composites
For this paper, twelve composite pipe joints were prepared. Among them, six were prepared using ultraviolet (UV) curing E-glass fiber reinforced vinyl ester composites and six were prepared using ambient environment curing E-glass fiber reinforced vinyl ester composites as control. Filament wound E-glass fiber reinforced vinyl ester composite pipes were used. Each section of pipe was 304.8 mm long with a 101.6 mm inner diameter. The wet lay-up technique was used to prepare the test samples. The curing time for the UV cured samples was 40 minutes, while the curing time was 24 hours for the control samples. Both internal pressure tests and four-point bending tests were conducted on the UV cured and control samples. The test results show that the UV cured FRP wrapped composite pipe joints achieved nearly the same bending strength as the control samples. However, the internal pressure rating achieved by the UV cured FRP coupled joints were lower than those achieved by the control samples. Based on the test results, the UV curing FRP can be used in joining composite truss structures and composite frame structures. Further investigation is required in order for the UV cured FRP joined pipes to be used to transport liquids or gases under pressure.
Surface Treatment of Polymers and Composites with UV Light in Air to Improve Adhesion
Ultraviolet (UV) surface treatment of polymers in air has been used to successfully modify polymer surfaces in order to enhance adhesive performance and wettability in a cost efficient manner. A wide variety of polymers including thermoplastics (TPO, PP, PC, PMMA), thermosets (Epoxy, Vinyl Ester), rubbers and composites have been successfully modified with this UV treatment. Improvements in adhesive bond strengths from 100-600% can be realized for hydrophobic polymers such as TPO and PP with treatment times on the order of 30-120 seconds. Several key process parameters for UV treatment have been identified. UV radiation in the 180nm-300nm was found to be necessary for surface modification of polymers. The extent of surface modification was found to be strongly dependent on the ozone concentration. The surface temperature during treatment was also found to be a controlling factor for some polymers and preliminary evidence points to a relationship between the optimum treatment temperature and the glass transition temperature (Tg) of the polymer substrate.
Development of Methods for Assessing the Chemical Compatibility of Thread Sealants Used with Plastic Fittings
Thread sealants have been used to help ensure a leak-tight joint and reduce friction during installation between threaded metal pipe and fittings for over 100 years. Thermoplastic fittings using the same taper thread cannot be assembled as if they were metal due to chemical compatibility and maximum material stress. However these same sealants are often used on a plastic fitting joint. This may be done either because the installer has been trained to use the same sealants on all threaded joints, or because the plastic parts are not fitted properly and are leaking under pressure. Unfortunately, sealants that work well and are compatible with metal pipe threads may contain stress-cracking agents that will cause failure in plastic fitting joints. Because it is unlikely that the industry practice of using thread sealants will change in the foreseeable future, a method is needed to evaluate these products to determine compatibility with existing fittings materials and designs. The current work develops three categories of testing using tensile, flexural, and threaded part configurations. Several variations in each of these methods are attempted, with multiple types of sealants and materials. There is a definite trade-off in test duration and complexity of the test method. The results of this testing program are provided, with analysis of the failure types and recommendations for the development of an ASTM test method.
Mechanical Properties of Rotationally Moulded Nanocomposites
Polyethylene montmorillonite and quaternary tallow ammonium chloride modified montmorillonite nanocomposites were prepared by melt blending. The effect of compatibiliser concentration on composite mechanical properties was investigated. The nanocomposite morphology was examined using wide angle X-ray diffraction and scanning electron microscopy. Primarily intercalated structures were observed. The nanocomposites prepared were rotationally moulded using a peak internal air temperature of 200°C and an oven temperature of 300°C and injection moulded samples using a nozzle melt temperature of 220°C. No significant variation was evident in the shrinkage and warpage characteristics of the rotomoulded parts. The tensile, flexural and impact properties of specimens taken from both the rotomoulded and injection moulded parts varied with compatibiliser content. Generally, the properties of the injection-moulded parts were superior to that of the rotomoulded parts.
Interrelationships between Fatigue and Creep Fracture in Poly(ethylene) and Poly(vinyl chloride)
Using a fracture mechanics approach, a dynamic fatigue methodology was developed to accurately predict creep fracture in both poly(ethylene) and poly(vinyl chloride). The predictive methodology applied to cases in which the crack propagated in either a stepwise or continuous manner. The effects of material variables such as molecular weight and impact modifier were also elucidated.
Modelling Impact Fracture and RCP Resistance of Thermoplastics from Cohesive Properties
Developers of thermoplastic materials for pressure pipe applications must design them to resist rapid crack propagation. However, they are usually able only to test them for resistance to impact. The hypothesis that both failure modes are dominated by adiabatic heating leads to good quantitative predictions for each property - and hence to an account of the relationship between them. Here, the model based on this hypothesis is extended to explore the influences on fracture resistance of molecular weight and of thermal property non-linearity.
Residual Strain Characterization Using an Embedded FFB Sensor: Measurements and Simulations
Residual strains in an epoxy specimen are investigated using embedded Fibre Bragg Grating sensors. A novel OLCR technique allows the direct reconstruction of the optical period and provides the strain distribution due to epoxy consolidation along the fibre. The experimental data show an excellent agreement with finite element simulations.
Polyethylene Nanocomposites – Investigating the Tensile Properties of Polyethylene Nanocomposites for Rotational Moulding
Rotational moulding is continuously expanding into new markets which require improved material properties and shorter cycle times. Conventional PE, used in over 80% of the rotational moulding market is a relatively low strength material therefore high part wall thickness, long cycle times and design limitations are imposed.The development of polymer/clay nanocomposites has shown significant improvements in mechanical properties with small additions of organoclay, which have the ability to improve mechanical performances or reduce cycle times.In this work the effect of organoclay on the tensile properties of PE nanocomposites at a range of temperatures was investigated. Tests were also conducted at a range of cross head speeds (CHS) to illustrate the effect of slow rates of extension and instantaneous loading. Tensile testing shows the final nanocomposite properties depend significantly on organoclay loading with improvements of 25% in tensile modulus at room temperature and larger improvements at higher test temperatures being reported. The results also indicate the organoclay loadings investigated had an adverse effect on the tensile yield stress.
Investigation of the Processing Characteristics and Mechanical Properties of Metallocene Catalysed Polyethylene Foams for Rotational Moulding
The object of this work is to investigate the foaming characteristics of three grades of metallocene-catalysed Linear Low Density polyethylenes for rotational moulding using both an exothermic and endothermic chemical blowing agent. This paper reports on the results of ongoing experimental investigations in which rheological and thermal parameters are related to the polymer structure and mechanical properties. Through adjustments to moulding conditions, the significant processing and physical material parameters, which optimise metallocene catalysed linear low-density polyethylene foam structure, have been identified. The results obtained from equivalent conventional grades of Ziegler-Natta-catalysed linear low-density polyethylene are used as a basis for comparison.
The Effect of Coupling Agents on Foaming with Polymer Microspheres in Rotational Molding
The use of polymer microspheres for producing microcellular foams is a new development in rotational molding. In previous studies, some reduction in mechanical properties has been found due to the immiscibility between the polymer shell and the matrix polymer. Coupling agents can act as a molecular bridge at this interface and can also affect bubble growth by altering the rheological properties of the matrix polymer. The influence of different coupling agents on the melt properties of several resins was investigated, as well as the effect of these coupling agents on the mechanical properties of foamed rotationally molded parts.
Manufacturability of Fine-Celled Cellular Structures in Rotational Foam Molding
Any closed-cell polyolefin foam production tends to achieve the highest possible cell size distribution uniformity, cell size reduction, and cell density augmentation. However, the control of the cell size of rotationally foam molded cellular structures formed on the base of a chemical blowing agent (CBA) might be often aggravated by some inherent limitations that are unique to the rotational molding process, which results in coarsercelled final cellular structures being yield. Although a finecelled morphology (cell size < 100 [?m] and cell density > 106 [cells/cm3]) in rotationally molded foams has been closely approached, it has not been actually achieved yet, nor it has been ever clarified whether it is actually achievable in rotational foam molding or not. This study attempts to provide an answer to this fundamental question by focusing on the understanding of the mechanisms governing the formation, growth, shrinkage, and collapse of CBA-blown bubbles in non-pressurized polymer melts originating from extrusion melt compounded foamable resins in a pellet form.
Oil Heating and Cooling Machines for the Rotational Moulding of Plastics
Forced air convection is the most common method for heating and cooling the mould in the rotational moulding process. However, it is generally accepted that this is a very inefficient method of heat transfer and so interest has grown in the use of more direct methods of heating and cooling the mould. This paper reports on an experimental study where oil was used to heat and cool the mould. This method is used commercially in a small sector of the market, but there has never been a detailed study of its effectiveness. The results to be presented in this paper show that oil heating and cooling of the mould offers much higher thermal efficiency and reduced cycle times. The performance of the oil heated machine is compared directly with a conventional hot air oven. It is shown that ovenless rotomoulding machines are more amenable to process control because monitoring equipment on the mould is easily positioned outside the heated environment.
Designing Impact-Modified Polypropylene for Durability
Polypropylene is increasingly being used as a structural load-bearing polymer in durable applications. Elastomer is usually added for impact toughness improvement but few studies address the selection of elastomer morphologies for resistance to failure due to load conditions over long time. This paper discusses the results of screening some polypropylene-elastomer blends for durability using a recently developed notch sensitivity methodology.
A Fatigue Approach for Lifetime Prediction of PE-HD Pipe Grades
Fatigue crack growth (FCG) experiments were conducted on two high density polyethylene (PE-HD) pipe grades with various test specimen configurations such as compact type (CT) and circumferentially notched bars (CNB). The effects of R-ratio and frequency on the FCG behavior were studied. While FCG rates showed a great dependence on R-ratio in terms of stress intensity factor range, the effects of frequency may be considered significant in the low crack growth region. These experimental data were employed for lifetime prediction based on the crack layer theory.
The Effect of Direct Electrical Heating on the Cycle Time and Mechanical Properties of Rotationally Molded Polyethylene Parts
Direct electrically heated oven-less rotational moulding machines have been introduced to the rotational moulding market over the past few years. Whereas some of these systems used composite mould technologies, the MECH™ system developed by PPA Teo of Ireland, employs conventional steel tools heated directly by electrical elements surrounding the mould. The elements are supplied with current though slip rings. This paper will present the results of an initial study into the moulding and cycle time characteristics of the MECH™ system and compares it with two types of conventional hot air rotomoulding machines. Machine efficiencies, as well as heating and cooling times have been compared for the three machines. The effects of processing parameters on the mechanical properties of the mouldings have also been assessed.
The Effect of Cooling Rate on Rotationally Molded Parts
The quality of a rotationally molded part is highly dependent on its cooling rate, perhaps more so than its heating rate. A trade off between part quality and cycle times is often necessary to ensure economical feasibility. This paper presents an overview of the effect of cooling rate on final part quality. The temperature profile through the part wall during cooling is related to the part’s mechanical properties, morphology, shape and general appearance. Six different mold cooling rates are investigated; they range from quiescent cooling (average 2C°/min) to water spray cooling (average 15C°/min).
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