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  • Soy-Based PU Foam Characterization

    Abstract

    Understanding the magnitude and mechanisms of the soy based polyurethane (PU) foams and properties of materials has implications on the application of this foams. Insulators protect devices from aggressive heat. However, due to the highly porous nature of the foams and the increase in interfaces due to fillers such as kenaf core, helps increase mechanical properties, while maintaining the light density of the foam. The effect of fillers on is a critical parameter in investigating the thermal properties and its effect on biodegradability. In this paper, we use thermal conductivity, compression values, and scanning electron microscopy (SEM) to understand the phenomena behind these results. Additionally a compostability test was performed to determine degradation under standard composting conditions.

    Keywords: thermal conductivity, MTS, Soy based PU, compostability, SEM

    Introduction

    The need for alternative foam products has become a priority in several fronts; foams are present in two main areas, food packing and insulations, with outstanding performance, low density and high thermal insulation makes them perfect, but both applications have a very short life cycle and then an undesirable recyclability or biodegradability.

    Polyurethane (PU) is one of the most versatile and intensively used industrial materials. By the proper selection of reactants and changing percentage of the component in the formula, the resulting polyurethane can be elastomer, thermoplastic, thermosetting, rigid and flexible foams. Rigid polyurethane foams can be used as construction materials, such as polymeric concrete components, insulating materials, sealants and signboard. One of the major components to make polyurethane, polyol, is largely relying on petroleum crude oils and coals as feedstock. However, bio-based polyols have been developed from vegetable oils such as soybean oil, canola oil, palm oil and castor oil, due to the environmental and sustainable issues in recent years ((Bergeret 2011), (Calmon 2000), (D' 2007), (Faruk 2012)) [1-5]. Developing bio-renewable feedstock for industry is crucial now for both the economic and environmental reasons.

    Soybean oil is an annually renewable natural resource for the polyols and is available in large quantities. For each pound of soybean oil produced, 2.67 pounds of carbon dioxide are removed from the air [1]. Soy-based polyols can be used in various polyurethane applications by selecting proper functional groups and side chains. Polyurethanes produced from soy-based polyols normally exhibit equivalent or improved physical and chemical properties due to the hydrophobic nature of triglycerides.

    The selection of the Kenaf core is due to the great availability, representing more than 60% of the Kenaf plant, and not being as desired as the fiber portion of the plant that has a higher demand, the core also has a particular property that make it more desirable on foams, it is hydrophobic, composites has increased the global demand for natural fiber crops. Kenaf is an annual species of fiber crop which can grow to around 9 feet in 9 months.

    When Composting PU together with other biomass waste, the biodegradation process can happen within two weeks and the materials will be fully decomposed, having disappeared within three to four weeks. Since the introduction of the Soy base PU, we decided to verify the industrial compost ability of the foams and its rate. A final verification was needed to determine the degree of toxicity in the remaining compost, Phytotoxicity, a detrimental deviation from the normal pattern of appearance and growth of plants in response to a given substance, is designed to assess potential effects of substances on seedling emergence and growth. As such it does not cover chronic effects or effects on reproduction. Passing this test is without doubts a major indicator of the compost suitability of final our product at the end of the life cycle (Test No. 208: Terrest...).

    The main objective of this research was to develop soy-based polyurethane foam reinforced with Kenaf core and to investigate thermal properties, furthermore, the effect of Kenaf core addiction when foaming the composite, the standardized compostability capacity of the foam in the whole spectrum of samples and a final phytotoxicity test to proof a safe waste at the end of the life cycle.

    The main objective of this research was to develop soy-based polyurethane foam reinforced with multi-walled carbon nanotubes to enhance the compressive and mechanical properties. Soy-based polyurethane / carbon nanotubes composites with loadings of 0.5 and 1.0 wt% were synthesized. The effects of kenaf content on the properties of soy-based polyurethane foam composites were investigated.

    Experimental

    Materials

    The soy based polyurethane Eco-Pur©325-6 was provided by Demilec Inc. and samples were created at their facilities. The resin contains responsibly made polyols that were made from soy oils, recycled plastics, and new generation blowing agent that has zero ozone depleting potential.

    The commercial grade Kenaf Core 2000, supplied by USDA, The Kenaf core (Hibiscus Cannabinus) was selected due to the high availability and low density of 0.28 \( g/cm^{3} \) with an average particle size of 150 \( \pm \) 20 \( \mu m \).

    The municipal compost for the biodegradability test was provided by Dyno Dirt products, and finally the seeds for the Phytotoxicity test, Peas and Cucumber are supplied by MBS Seed Ltd. And American Seeds.

    Foam and Composite Preparation

    Samples were prepared at the Demilec Inc. facilities in Arlington, Texas. Part A and Part B were mixed at 100 to 100 volume ratio or 110 to 100 weight ratio, respectively. For the preparation of the composites, kenaf core was added at 5, 10, and 15 weight percent.

    Thermal Conductivity

    The thermal conductivity in the axial direction of the samples was taken using a Hot Disk TPS 1500 Thermal Conductivity System [12, 13]. A thin-film heating element was placed between two identical samples and enclosed inside a chamber.

    Compression Test

    The cellular samples were made into circular shapes with a cross-sectional area of 500 \( mm^{2} \) and a thickness of approximately 20 mm. The tests were conducted on a hydraulic MTS machine under room temperature at 25\( ^{\circ} \)C at a crosshead speed of 0.5 mm/min. The load-displacement curves were used to collect the resulting stress-strain graphs. Compression strength and modulus were obtained by ASTM D1621.

    Scanning Electron Microscopy (SEM)

    FEI Quanta Environmental Scanning Electron Microscope (ESEM; FEI Company, Oregon, USA) was used to image the surface of foams and composite-foams at an accelerating voltage of 12.5 kV. The sample was sputter coated with a metal compound and used in low- vacuum mode in order to obtain images.

    Automated Multiunit Composting System (AMCS)

    The compost test was conducted using the automated multiunit composting system designed by Pickens [14], it is an automated and reliable systems due to the direct measurement respirometer. This composting system complies with the ASTM D-5338 (latest edition) and equivalent to the ISO 14855. The method is similar to the one used by Anne Calmon and Thitisilp Kijchavengkul [2, 9]. The whole process is performed at a regulated composting temperature and humidity of 58\(^{\circ} \)C (\( \pm \)2C) and above 50% respectively.

    The PU polymer samples, were introduced into the Compost Unit, then the following sets (3 samples each) were prepared to complete the required process, each one containing 200g per reactor.

    Well aerated compost, 2 months old, derived from a commercially operated composting plant of municipal solid waste, and was used as inoculum. Glass, stones or metal particles were removed after which the compost was sieved through a screen of about 8 - 10 mm to obtain a homogeneous inoculum of sufficient porosity, which did not have to be improved due to the presence of small wood particles, The pH of the compost was verified at the beginning and at the end using an Oakton Acorn pH 6 meter, reporting a pH of 7.80 and 7.15 respectively.

    The composting system is an aerobic composting system that measures the input CO\( _{2} \) through the even air supply to composting reactor and the output CO\( _{2} \) from the reactor, the net CO\( _{2} \) emitted by the composting itself is the result of output minus the input. There are several bioreactors designs, depending of the CO\( _{2} \) measuring method and this one is simple and accurate with over 15,000 measurements per day acquired through Labview software into data files. [3, 7,8,9,13]