SPE Library

In recent years, pressure from economic and environmental requirements has been experienced in the field of polymer production. This trend towards single stage operational units, in processes such as low shear devolatilization of elastomer solutions, radical polymerization and polycondensation reactions, phase changing processes and the conversion from batch to continuous operation continues and has lead to the development of large volume, twin shaft horizontal processors (LVPs).These processors have been designed for applications requiring medium to long residence times (20-120 minutes).As an example of this new family of processors, the multi-purpose Reasol®, a new counter-rotating twin shaft processor, is introduced. Trials with model polymers have been performed in a 60L unit at the developer's test center. Its performance is described here by power consumption, RTD (residence time distribution) and self-cleaning and devolatilization efficiency.Trials show that product transport through the new LVP is characterized by a narrow RTD with a high degree of self-cleaning. Typically, the RTD exhibits a Peclet number in the region of 25-35. It is also shown that, unlike typical twin-screw extruders, the shape of the RTD curve is largely unaffected by the rotor speed or mass rate. Furthermore, rotor speed has a relatively small effect on mean residence time thus allowing the freedom to optimize rotor speed with respect to other processing objectives such as heat transfer, surface renewal or shear rate.The indications are that the characteristics of the RTD, power consumption and devolatilization are analogous to more traditional equipment such as twin screw extruders in spite of the larger free volume and residence time and the lower shear.The new LVP is commercially available up to sizes of 12,500 litres net processing volumes.

In this work, an extrusion process has been developed for the devulcanization of rubber crumb from recycled tires employing supercritical CO2. For that purpose supercritical CO2 has been injected in a twin screw extruder to swell the rubber crumb and to facilitate the otherwise impossible rubber extrusion process. As a consequence, waste rubber can be processed under mechanical shear and extensional forces at various operating conditions that may lead to different degrees of devulcanization.

Biocomposites such as particleboard and medium density fiberboard are currently made with formaldehyde-containing adhesives. Since the government is continuously developing and implementing very stringent regulations to eliminate formaldehyde emissions into the environment, alternative approaches must be developed to replace these adhesives. This study examined the concept of using a reactive extrusion process as a means of developing a new, formaldehyde-free binding system for wood composite products. The surfaces of wood particles were modified by grafting maleated polyethylene through a continuous reactive extrusion process. Chemical changes resulting from this treatment were followed by studying the FTIR and XPS spectra. The modified wood particles were compression-molded into panels, which were tested for bending properties. Both FTIR and XPS data revealed that the chemical reactions have taken place between the hydroxyl groups of wood particles and maleated polyethylene. The modulus of rupture (MOR) results showed that the composite panels compared favorably with current standard requirements for particleboard.

This work presents the effects of incorporating post-consumer and post-industrial recycled HDPE to their virgin counterparts and to LDPE in different contents to produce tubular film for packaging. Tensile, surface and optical properties for each blend were measured.A reduction in the HDPEs blends physical properties and an increment in those of the LDPE/recycled HDPE blends were obtained as the recycled HDPE component was increased.

Failures of plastic components are being seen more often in industrial, household and commercial settings. Many of these failures involve the transport of water and cause significant damage when they occur. These failures can be caused by improper material specification, bad design, over loading or incorrect molding conditions. Issues such as chemical resistance, environmental deterioration, geometric sensitivity, temperature dependence and aging are at times overlooked.

Eco-friendly green" composite materials are fabricated from inexpensive chopped natural fiber and poly(3-hydroxybutyrate) (PHB) through extrusion followed by injection molding processing. The incorporation of natural fiber in to the composite structure improved the modulus and impact strength of virgin bioplastic. Maleated PHB is synthesized by us and is also used as a compatibilizer in PHB based biocomposites."

Polymer blends such as result from recycling of postconsumer plastics often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell-population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Neat HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins due to the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well-developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. Improvement in impact strength was associated with well-developed microcellular morphology.

Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in an industrial scale twin-screw reactive extrusion system. Reactive extruded recycled poly(ethylene terephthalate) (RER-PET) samples at different PMDA concentrations were characterised in terms of rheological properties; thermal transitions and crystallinity. The results confirm the increase in molecular weight with an increase of PMDA concentration, and the formation of branching at concentrations above 0.25 wt.% PMDA. Structural changes due to PMDA addition affect the Tm, Tc and the crystallinity; however, no significant change was observed for the Tg.

The renewable polymers are environmentally friendly and naturally biodegradable, and could serve as an inexpensive source of raw material for single-use engineered products. Efforts are underway to develop ecocompatible consumer plastics by incorporating renewable polymers as an alternative to petroleum-derived chemicals. Therefore, gaining fundamental understanding of biobased polymers is critical for the design and development of consumer products. The research efforts at the USDA laboratory pertaining to the development of biopolymer blends, polymer processing, characterization and lifetime evaluation are presented.

The objective of this research is to determine the effect of thermal cycling on the development of microcracks in BMI-carbon fiber composites (5250-4 RTM / IM7 6K 4-harness satin weave fabric). By clamping composite specimens on the radial sides of two half cylinders having two different diameters (127mm and 70mm), two different pre-stresses (-0.4 to 0.4 GP and -0.7 to 0.7GPa) are applied to the composites. Three different thermal cycling experiments, 1) –196°C to 250°C, 2) 23°C to i)150°C ii) 200°C iii) 250°C, and 3) -196°C to 250°C were performed as a function of pre-stress, number of thermal cycles, heating or cooling rate, and humidity conditions. An in-situ monitoring microscope is used to observe the microcrack development under synergistic stress, time, and temperature conditions. The experimental results suggest that there is a higher probability of microcracking with increasing number of thermo-cycles, higher pre-stress and humidity. A mathematical model considering residual stress and pre-stress is suggested to predict the microcracking under environmental conditions.

This paper probes a hypothesis for initiation of environmental stress cracking (ESCR) based on a thermodynamic criterion for localized swelling induced by stress on the polymer. The system chosen for study is polycarbonate with oleic acid. An experimental technique involving contact angle measurements of a sessile drop as a function of stress is presented. A novel technique for contact angle measurements using refraction is also introduced.

A layout design of a platenless injection molding machine is developed. The machine design is motivated by economics, energy efficiency, compactness, ease of use, and environmental friendliness. The elimination of traditional platens allows for significant performance improvements as well as flexibility of new injection system and mold designs. This paper establishes theoretical feasibility, but also indicates that the design is most appropriate for clamp tonnages less than 150 tons due to actuator power and mold deflection limitations.

Composites of post-consumer plastics and high volume fraction waste paper have been studied. Various production techniques have been tested, with an optimum processing method defined, allowing the manufacture of low-cost composites of up to 60% paper content. Results indicate increases in tensile, flexural and creep modulus and flexural strength compared to the matrix can be achieved without the requirement of additives, with only marginally lower tensile strength and brittle impact behavior.

While epoxy thermosets are commonly used and are best known for their high glass transition temperature (Tg), creep resistance, environmental resistance and high stiffness, they are extremely complicated and intractable to thorough investigation. This is in part due to the fact that these are curing systems and gelation marks a turning point in the system’s performance as well as ability to be probed for effective structure-property relationships. In addition, practical formulations often contain multiple components that have subtle but important interactions to the final performance.In this presentation we will cover work that was performed recently to quantitatively probe the effect of one such practical yet important effect, namely chain termination. The effect of the size as well as flexibility of the chain termination group will be examined via a controlled host matrix chemistry that comprises of DER™ 332 as the epoxy, bisphenol A (BA) as extender and tris(4- hydroxyphenyl)ethane (THPE) as a crosslinker. Data and trends pertaining to Tg, stiffness, yield strength, fracture toughness and thermal expansion coefficient will be discussed.

An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end-capping and plasticization.

The Non-Linear Strain Energy Equivalence Theory, a semi-empirical model, is utilized to predict long-term creep from short-term compressive stress-strain experiments conducted at different strain rates. Stress-strain experiments in uniaxial compression are performed at strain rates of 3 and 0.03 %/minute to predict creep behavior and stress-strain data at several strain rates for an immiscible polymer blend of recycled fractional melt flow high-density polyethylene and recycled polystyrene. The creep behavior is predicted up to 50 years at stress levels of 400 and 800 psi.

New Capillary Viscometers, beyond offering remarkable precision, may also broaden the characterisation of polymer compounds.After a short review of the features of recent equipment, some selected examples of applications will be shown. They range from improved quality control of incoming and outgoing products, to recycling management, masterbatches characterisation, and evaluation of dispersion effects on filled materials.

Poly(lactic acid) (PLA) is being investigated vastly due to its biodegradable and biocompatible nature. However, the degradation of PLA is slow, often leading to a long life-time in vivo. The major objective of this research is to modify PLA film surfaces with the ultimate aim of making a bioactive surface that will show faster degradation. The PLA film was solvent cast and the film surfaces were grafted with poly(acrylic acid) (PAA) using a UV induced photopolymerization process. The films were incubated in different pH solutions, viz., pH = 4, 7, and 10, for a specified time period. The film resulting from each treatment was analyzed using Transmission-FTIR spectroscopy and Atomic Force Microscopy (AFM). The molecular weights of the films were measured using gel permeation chromatography (GPC). Results established that faster degradation of the PLA film when incubated in different pH solutions could be achieved by surface modification of the PLA film by grafting PAA.

This report will include the way to design, fabricate, and assemble a Polymer Electrolyte Membrane Fuel Cell (PEMFC) to maintain a low voltage source, near one volt, that runs at operating temperatures near 80 degrees Celsius. Creating a stack of cells will provide an energy solution that is more efficient than the system in place today. The PEMFC runs off of pure hydrogen and air (oxygen) and will provide a power source that is non-pollutant and renewable since hydrogen is readily available through the electrolysis of water. The problems with this experiment are maintaining moisture control on both the cathode and anode and the other problem is in controlling the hydrogen gas supply since hydrogen is very explosive when combined with oxygen. With these problems taken into consideration the PEMFC could be the energy source for the future.

The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.