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Plastic Pipes and Fittings
Analytical Characterization of Commercial Foams for Consumer Bedding Applications
The objective of this study was to characterize popular commercial bed-in-a-box mattress and visco topper foams, which are the benchmark bedding products in the market. These products were advertised as gel infused foams that offer superior thermal conductivity and support. Multiple techniques were utilized to identify the composition of the foams. In summary, the commercial “green” and “gray” bedding polyurethane (PU) foams were similar in composition, and they were made of glycerin-initiated PO/EO based polyols. It also showed the incorporation of styrene-acrylonitrile (SAN) in the polymer backbone. The isocyanate part was consistent with an aromatic isocyanate identified as methylene diphenyl diisocyanate (MDI). In addition, the blue gel polymers that were infused to these foams were polyurethane based material. Furthermore, the black particle in the “gray” foam that was advertised as heating wicking material was graphite-based additive.
Degradation of CPVC Sprinkler Piping Material By Simulated Sunlight and Uvb Light
The effect of simulated sunlight and ultraviolet (UVB) light on the chemical structure and tensile properties of chlorinated polyvinyl chloride (CPVC) was studied. Exposures were conducted in a Q-SUN xenon arc chamber and QUV accelerated weathering tester. CPVC tensile specimens were exposed for 1 week, 4 weeks, 8 weeks and 12 weeks and then analyzed using a tensile testing apparatus and Fourier Transform Infrared (FTIR) spectroscopy. The testing showed the CPVC material exhibited early degradation when exposed in the Q-SUN xenon arc chamber. FTIR analysis showed surface chemical structural changes as early as one week into the exposure and tensile testing showed apparent changes in elongation at break (70 % reduction) after 8 weeks of exposure in the Q-SUN xenon arc chamber (equivalent to 1344 hours of noon summer light) with a day light filter and 67.66% reduction in the elongation at break after 12 weeks of exposure in the Q-SUN xenon arc chamber with a window glass filter. CPVC tensile specimens when exposed in the QUV accelerated weathering tester exhibited discolored or stained surfaces.
Foaming of PVC Using Ultra High Molecular Weight Acrylic Processing Aids
Polyvinyl Chloride (PVC) foaming was studied as a function of high molecular weight acrylic processing aids. It was demonstrated that an ultra-high molecular weight processing aid is 25-30% more efficient than relatively lower, but still high, molecular weight acrylic processing aids. The higher Mw processing aid provided similar foaming performance at lower loading levels. Foaming reduced the density of PVC compounds to 0.32-0.34 g/cc. More than 1000% expansion was achieved in the melt extrusion process using a chemical blowing agent. Fusion characteristics were also studied. Fusion times for initial fusion peaks were in the range of 42-44 seconds while the fusion times of the second fusion peaks were in the range of 74-94 seconds. The higher molecular weight processing aid maintained fusion characteristics of PVC compounds, warranting no significant changes in extrusion process.
Morphology and Mechanical Performance of Pipe Grade HDPE Exposed to Chlorinated Water
Thin samples of a pipe-grade polyethylene with a bimodal molecular weight distribution were exposed to 5ppm 70C chlorinated water for up to 3000 hours. The samples were characterized by tensile tests, size-exclusion chromatography, infrared spectroscopy, and differential scanning calorimetry. Throughout exposure, the molecular weight data showed evidence of degradation: weight-average molecular weight was reduced, and a shift in the molecular weight distribution from a bimodal to a unimodal distribution (decreased dispersity). After 2250 hours of exposure, brittle behavior was observed, in which the average elongation at break was 12%. At this level of degradation, the weight-average molecular weight was 9 % of its undegraded value, and the crystallinity had increased from 70% to 85%. Average tensile strength was reduced from 31.8 to 16.6 MPa. The data imply that the presence of short-chain branching may inhibit chemicrystallization and subsequently delay the onset of brittle behavior.
Reverse Engineering and Failure Analysis of Materials and Polymers Using Infrared and Raman Spectroscopy
Failure analysis and reverse engineering can greatly expedite product development. Infrared and Raman spectroscopy is the among the most powerful tools for this application because each molecule has a unique infrared and Raman signature. Infrared and Raman microscopy was successfully used to identify foreign particles on elastomers and to depth profile multilayer polymer film. Details of the measurement techniques are discussed.
Multi-layer Co-extruded Annular Structures Burst Pressure Performance
Recent developments in the area of multi-layer co-extrusion have led to the ability to produce annular structures with high numbers of very thin layers. The burst pressure of these pipe structures was investigated. It was observed that die head rotation can have significant impacts on the mechanical properties of these structures due to the elimination of weld lines as well as biaxially orientation effects in the annular structures. It was also observed that following the elimination of the weld lines, the burst strength increases, possibly due to the biaxial orientation effects at higher rotation speeds.
Novel Method of Compounding Cellulose Nanocrystal Suspensions into Polylactic Acid and Polyvinyl Acetate Blends
Cellulose nanocrystal (CNC) suspensions were compounded into blends of poly(lactic acid)(PLA) and poly(vinyl acetate)(PVAc) using a novel wet compounding approach in which drying and compounding werecarried out simultaneously. The resulting CNC/PLA composites were compared with those produced using a more traditional method of freeze-drying CNC suspensions followed bymelt-blending into PLA. CNCs in wet compounded composites appeared to be well-dispersed in the PLA/PVAc blends, and films extruded from these compounds exhibited high transparency compared with melt-blended composites. Gel permeation chromatography indicated that molecular weight degradation due to wet compounding was comparable to that from melt blending. The formulation, including surfactant modified CNCsand PVAc processing aids, played a significant role in the dispersion and properties of the nanocomposites. The elimination of a stand-alone drying stepfor cellulose nanomaterials can potentially overcome some of the challenges associatedwith producing thermoplastic cellulose nanocomposites and help advance commercialization of these materials.
Reduced Order Kinetic Model for Corrosion of High-Density Polyethylene in Bleach Solutions
A reduced order kinetics model is proposed for the corrosion of polyethylene in bleach solution. Hypochlorous acid (ClOH) is considered as the oxidizing agent which is formed from the hydrolysis of bleach. The model simulates the diffusion of ClOH into the non-polar polymer matrix followed by its dissociation into radicals. The reaction between the radicals and the polymer is phenomenologically modeled using an ordinary differential equation. The model is suitable for coupling with mechanical models for life-time analyses of polymers members under mechanical loading and exposure to corrosion. The model captures the effect of the chain oxidation process which causes the accelerated aging of the polymer.
Studies of Material Properties of Htpb- Based Composite Under Aging Conditions
Hydroxyl-terminated polybutadiene (HTPB)-based rubber composite is usually used for solid propellant binder. In order to investigate the long-term material properties in the storage environment, it is recommended to set up the conditions refer to MIL-STD-810G. After aged for 100, 200, 300 hours with different temperature and humidity conditions, the key properties, i.e. tensile test, Fourier transform infrared spectroscopy (FTIR), and surface morphologies were examined. Also, by using these experimental data, diffusion model using finite element method suggested. This study will be useful for the life evaluation of HTPB-based composites considering diffusion.
Submicron Texturing of Injection Molds Using Femtosecond Laser
In injection molding, part thickness reduction is the main leverage to decrease process cost and material consumption. However, low thickness cavities require high pressure to be replicated. Controlling the surface properties of the mold/polymer interface can be a solution for drag reduction. Conventional micro- and nano-texturing technologies requires clean room environment, high-cost equipment, and are based on time-consuming multi-step processes. In this work, we presented a novel approach to sub-micron texturing of steel injection molds using femtosecond laser. A high-frequency and high-energy laser source is used to create regular and homogeneous ripples. The effect of these structures on the injection molding process are here discussed, showing how texturing can be used to reduce the injection pressure and promote wall slip.
The Complexity of Service Life Prediction For Polyolefins In Chlorinated Disinfectants
Despite much effort, it is still very difficult to predict the service life of polyolefins when used in contact with the chlorinated disinfectants; chlorine, chlorine dioxide and chloramines. The actual degradation mechanism, both for the degradation of the additives and the subsequent, or in some cases parallel, degradation of the polymer, is still under debate. Also, it is not really that well known if chemical or physical properties are the most decisive in improved resistance to disinfectants. How much effect will the morphology, number and lengths of side chains, creep resistance, density, crystallinity, type and amount of stabilizer, number of tertiary hydrogens, double bonds, processing quality, solubility and diffusion rate of stabilizers, disinfectant and oxygen etc play? Since it is very difficult to change just one parameter at the time, this is quite difficult to investigate. For hot water pipes the aim is to have at least 50 years’ service life. Today the ASTM F2023 is used to test if a material will achieve this service life or not. Even if this testing is quite time consuming, with exposure times at the lowest temperature up to two years, or even longer, its validity to really predict the service life is quite questionable. The ASTM F2023 method is a pipe and materials test not a systems test and discards failures at fittings, while in fact this is often where the failure in service appears. In recent years a number of papers and presentations have been made presenting alternative accelerated testing methods and possible degradation mechanisms but very little can be found in the literature on investigations of pipes taken out of service and the correlation between the accelerated ageing with actual failures. This paper aims at describing the complexity in accelerated ageing and service life predictions of polyolefins in chlorinated disinfectants.
Thermal Derating Factors for Fused PVC
The use of PVC pipe has been expanded in the most recent edition of AWWA C900-16. Once solely for drinking water, the AWWA C900 standard now includes reclaimed water, irrigation water, wastewater, or any other fluid compatible with nonplasticized PVC. When limited to drinking water, there is relatively little use for PVC to operate at elevated temperatures. The scope increase including industrial, raw water, geothermal, and other opportunities now make the use of PVC pipe viable so long as the pipe can meet temperature and pressure requirements. The hypothesis tested is that the present set of thermal derating factors may contain room for adjustment with the present PVC pressure pipe extrusion formulations and technology. This presentation details out the test methods used to screen and then develop derating guidance for fused PVC pipe. Screening methodology and results to validate the hypothesis are discussed. With positive results from the screening, the long term testing done to develop an alternative set of derating factors is also included.
Transition From Ductile Failure To Brittle Fracture of High Density Polyethylene Under Creep Loading
Uniaxial creep tests on notch-free specimens were conducted on unimodal high-density polyethylene (HDPE) over a wide range of stress and temperature. As expected, occurrence of ductile failure or brittle fracture was found to depend on the applied stress and temperature. In this work, a stress-time-temperature (StT) expression was established to construct the master curve of stress versus creep time to ductile failure (or brittle fracture) at a given temperature, which contains the transition between the two behaviors (commonly known as the DB transition). For the unimodal HDPE used in this study, critical stress for the DB transition was found to decrease significantly, from 11.43 to 6.50 MPa, by increasing test temperature from 296 K to 358.5 K. The corresponding time also reduced considerably, from over 560 hours at 296 K to about 6 hours at 358.5 K. In addition, critical stress for the DB transition shows a good correlation with one characteristic quasi-static stress that we reported before. Such a phenomenon sheds a light on the possibility of using a short-term test to characterize DB transition of PE pipe.
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