Development of hydrophobic polyurethane/castor oil biocomposites with agroindustrial residues for sorption of oils and organic solvents

https://doi.org/10.1016/j.jcis.2020.07.091Get rights and content

Highlights

Abstract

Since pollution of aquifer sources by organic compounds is a threat to the environment and humans, technology's constant advancement in developing sustainable adsorbents using renewable resources with hydrophobic characteristics has become increasingly attractive. In this study, we developed and characterized castor oil-based polyurethane biocomposites reinforced with malt and/or acerola residues for adsorption/separation of various organic oils/solvents. The residues evidenced biocomposite flexibility, increase in adsorption capacity for all organic oils/solvents, with a maximum of 3257.8 ± 55.6% for chloroform in 60 min and hydrophobicity (144 ± 0.2°) in acidic, saline and alkaline environments, and when exposed to UV radiation. These biocomposites can be quickly and repeatedly recovered by simple hand-tightening and solvent release systems (10 times) and vacuum suction filtration (20.5 ± 0.9 s/10 mL). Through the pseudo-first order (PPO) and pseudo-second order (PSO) kinetic models, the engine oil adsorption capacity increased with time from 746.7 ± 77.4% (60 min) to 928.6 ± 16.7% (90 min). These bio-composites are prototypes to be used with malt and acerola bagasse residues, becoming a reference for future works, produced in a sustainable way, with high potential for application in treatment of effluents with organic pollutants.

Introduction

The organic contaminants generated by chemical industries not only pollute aquifers but also may promote other environmental accidents; for instance, an oil spill during sea transport causes tremendous environmental and energy issues, and economic losses. Furthermore, a steadily growing number of residues such as industrial wastewater containing oil and leakage of organic solvents insoluble in water (benzene, toluene, cyclohexene, and dichloromethane) also threatens public health and the terrestrial ecosystem [1], [2], [3]. Therefore, the development of efficient methods and materials able to remove organic pollutants from water is indispensable.

Conventional methods to deal with oil leakage, such as contention borders [4], chemical spreaders [5], in-situ burning [6], photochemical degradation [7], [8], bioremediation [9], and air pumping [10], have disadvantages and inefficiencies such as low liquid selectivity, a long cleaning period, and restrictions on component recovery.

The methodology studied in this work concerns the production of low-cost porous materials applied to an industrial adsorption process. These materials have shown to be an efficient and economical solution to the treatment of effluents with organic compounds. Certain materials with adsorption capacity can be used as a possible porous structure for the separation of oil/water solutions, for instance, meshes, textiles products, foams, and aerogel [46].

Thus, it is necessary to research new low cost porous materials for industrial use, where the success of adsorption as a separation process depends on the choice of adsorbent material and the optimization of process variables. According to Li, Zhang, and Wang [11], the amount of research about the usage of porous materials applied to the separation of oil/water is growing rapidly. Due to their excellent wetting properties [12] and low-cost [13], hydrophobic materials have also been used for the separation of oil/water solutions, adsorption and transport of oil.

Besides the attractive physical features, the use of materials derived from vegetable oils and residues are promising substitutes of petroleum-based chemical products, due to their non toxicity, effective cost, biodegradability, and intrinsic flow, all of which facilitates their use as raw material for polymer production [14].

Among numerous vegetable oils, castor oil (CO) is a trifunctional polyester polyol with a hydroxyl group that can be used as a substitute for the polyol of fossil origin for the synthesis of porous and biodegradable polyurethane (PU) foams. This oil, one of the most important renewable resources with a triglyceride of various fatty acids, has a high content of C18H34O3 ricinoleic acid and a unique structure of cis-12-hydroxyoctadeca-9-enoic acid, 18-carbonated hydroxylated fatty acid [15], [16]. The benefits from castor oil obtained from agro-industrial waste, which is occasionally discarded incorrectly, have been little exploited. Discarded castor oil could be used in the manufacture of foam composites to improve their physical and chemical properties, for example, to obtain obtaining more flexible and porous structures, increasing and to increase their adsorption and reuse the capacity of polyurethane foams. Furthermore, castor oil is a viable, sustainable, and low-cost alternative.

The specific by-product of agro-industry used in this study was bagasse malt (BM), which represents 85% of the by-products generated in the brewing industry. The global annual average production of BM is approximately 39 million tons [17], suggesting that alternatives for the correct exploitation and management of barley bagasse malt are necessary [18]. Another by-product used comes from a plant called Malpighia emarginata, found naturally in the Caribbean and South American islands, in Brazil, Mexico and certain regions of Southeast Asia and India, which produces an edible fruit known as acerola or Barbados cherry. During the processing of acerola, a substantial amount of residue (AR) is generated, causing losses of potentially useful raw material, and causing a negative environmental, social, and economic impact [19], [20].

This work aimed to develop vegetable polyurethane foam based on castor oil (Ricinus Communis) (PUCO) with agro-industrial residues. The result was expected to be a bicomponent polymer composed of a prepolymer and a polyol extracted from castor oil seeds with bagasse malt (BM) and acerola residues (AR) that would not emit toxic substances and be biodegradable. The foam was evaluated, through these residues, for its adsorptive power without modification of its structure in order to understand and evaluate the behavior and selectivity of the residues in the adsorption of contaminant/water of prepared materials. The biocomposite studied here is the first prototype reported in the literature to use malt and acerola bagasse residues for application in the adsorption of various oils and organic solvents. This makes it a promissory reference for future work with types of spongy adsorbents whether or not based on polyurethane.

Section snippets

Materials

The PUCO (density ≈0.07 g cm−1) was purchased from Imperveg® - Polymers Industry and Commerce Ltda, as component A (Methylene Diphenyl Diisocyanate - MDI) and component B (polyol, castor oil base). The BM was purchased from Pilsen beer production, which was collected after the enzymatic processing at the mashing stage, in an artisan beer production process; and the AR was obtained from drying experiments at the Food Laboratory at the Research and Extension Nucleus in Food-NUPEA, at the State

Characterizations

The ATR-FTIR analysis was performed in a Parkin Elmer 400 (Laborátorio de Combustíveis-UFPE-Brazil) with a resolution of 4 cm−1 and 16 scans. The morphology of the foams was evaluated with scanning electron microscopy (SEM) in an electronic microscope (EVO-LS15, Zeiss, Laboratório de Imunopatologia Keizo Asami-UFPE-Brazil). The thermal properties were evaluated through TGA analysis, which was performed in a thermal analyzer 2 STARe (Mettler Toledo/SuiçaSwitzerland, Departamento de Energia

Adsorption capacity

The initial experiments evaluated the adsorption capacity of organic oils/solvents by PUCO, PUCO-BM, and PUCO-AR foams, in the percentages of 5, 10, 15 and 20%, were performed in static system simulations. The specimens were immersed in organic oils/solvents (10 mL) at room temperature (23 ± 2 °C) for 60 min and then withdrawn for mass measurements (g).

Equation (1) represents the adsorption capacity in the static adsorption process.Ca%=wf-wiwi.100

Ca is the adsorption capacity, wi is the initial

Synthesis of foam and biocomposites

After the drying time of the residues, BM and AR were obtained in a 0.250 mm particle size (Tyler 60), for better adhesion and expansion in the matrix/reinforcement interface and better uniformity during polymerization in the biocomposition manufacturing process.

The chemical synthesis of PUCO developed here is based on the polymerization of diisocyanate groups and hydroxyl groups from castor oil-based polyol, as described in studies by Tenorio Alfonso, Sánchez & Franco [27] and Alaa, Yusoh &

Conclusions

The present experimental results showed advances in developing sustainable adsorbents using hydrophobic and renewable resources for efficient and easy oil/organic solvents/water separation, with future intentions to manufacture prototypes with larger dimensions and improvements for implementation in large-scale pumping systems and in more complex corrosive environments.

The PUOM foam with BM and AR agro-industrial residues was easily developed by the polymerization process to improve the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We are grateful to the National Council for Scientific and Technological Development (CNPq – Brazil 306574/2018-7 and 302788/2018-2) for financial assistance. Furthermore, we also would like to thank the Laboratories of the State University of Paraíba-UEPB, Integrated Laboratory of Petroleum Technology-LITPEG and to the Laboratory of Immunopathology Keizo Asami-LIKA for providing research facilities.

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