Development of fully organic coating system modified with epoxidized soybean oil with superior corrosion protection performance

https://doi.org/10.1016/j.porgcoat.2019.105523Get rights and content

Highlights

  • Multifunctional fully organic coating systems were fabricated and cured at the ambient temperature.

  • FTIR results signified the proper cross-linked structure among all organic components.

  • Soybean oil significantly enhanced the wettability and the thermal stability of the polymeric matrix.

  • EIS findings confirmed the ability of the fabricated organic coating system to ensure the long term corrosion protection.

Abstract

In this study, different loading ratios of epoxy resin (E) and epoxidized soybean oil (ESO) were introduced into acrylic–silicone polymeric blend with the presence of polyisocyanate (NCO) as the curing agent. The developed coating systems were applied on pretreated cold rolled mild steel substrates and the overall performances were investigated by means of Fourier transform infrared (FTIR) spectroscopy, contact angle measurements (CA), UV–vis analysis, thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS) and salt spray test. Moreover, the physico-mechanical properties of all developed coating systems were investigated. The obtained results revealed the ability of the combination of E and ESO at a certain concentration specifically, 9:1, to enhance the overall performance of the polymeric matrix as optimum curing level, better wettability, good physical-mechanical characteristics, thermal stability and significantly enhanced corrosion resistance were observed. The results also demonstrated the ability of the fabricated single-layer coating system to serve as a primer, topcoat or single coating system that has promising potential to be applied for decorative, self-cleaning, thermal insulation and corrosion protection purposes.

Introduction

Due to the growing awareness about the environmental issues, the global demand for functional bio-based products has dramatically increased over the past few years [[1], [2], [3], [4]]. Through this framework, sustainable polymers, environmentally friendly and biodegradable composite materials obtained from renewable resources such as plant oil are becoming highly recommended as bio-based products [[5], [6], [7]]. Among all the plant oils, soybean oil, particularly, is one of the natural oils that has been widely studied in research and extensively used in the industrial applications [[8], [9], [10], [11]]. Owing to its abundant availability, low cost, and non-depletable resources, soybean oil has attracted considerable attention due to its reactive functionalities such as the reconcilable conversion of the double bonds to a three-membered epoxide group which brings interests in polymeric uses. In conjunction with the exceptional molecular properties, soybean oil is widely used in many composite applications such as polyesters and polyurethanes [[12], [13], [14], [15], [16]].

The preparation of biodegradable polyester from soybean oil and its properties were investigated by W. Xuebin and W. Jincheng [17]. The study revealed that the prepared composites had a pronounced effect upon biodegradation property. K. Mizera and J. Ryszkowsk [18] studied the influence of different molar mass of soybean oil polyol into polyurethane elastomer and the results showed that the presence of the lower molar mass of soybean oil in the elastomer resulted in better observations for the tested parameters such as thermal resistance and physico-mechanical properties. On account of the profound findings and advantages of soybean oil, many recent approaches have been utilized to produce soybean oil derivatives such as the fabrication of epoxidized soybean oil (ESO) via epoxidation reaction which widely used as a diluent, plasticizer, and stabilizer [[19], [20], [21]].

Due to the fact that the composition of soybean oil is rich in unsaturated carbon-carbon double bonds, epoxidized soybean oil can be promoted via epoxidation reactions involving the reactions between the epoxide rings and the polymer network chains [[22], [23], [24], [25]]. On grounds of that, ESO is notably presumed as a derived renewable resource, biodegradable polymer, available and affordable material that has arisen interest in many research areas as a reactive modifier and stabilizer. It has been reported that ESO can influence the thermal stability, adhesiveness, and flexibility properties of the modified polymeric blends [26,27]. Lee et al., have reported the enhanced adhesive performance of the developed pressure-sensitive adhesive systems composed of triblock polyesters combined and a rosin ester tackifier with the presence of ESO as the plasticizer. The reported results showed that the combination of triblock polyesters blended with plant-based materials has enhanced the adhesion properties of the compound [7]. Moreover, Jian et al. have reported two efficient approaches to fabricate epoxidized soybean oil (ESO) thermosets with the enhanced performance [28,29]. These studies describe the increase of the crystallinity of the cured epoxy thermosets by the utilization of long-chained and crystalline curing agents namely, oligomeric poly (butylene succinate) [28] and dicarboxyl-terminated polyamide1010 oligomers [29]. The results revealed the vital role of the biobased curing agents in altering the overall performance of the ESO based thermosets with pronounced better mechanical properties and thermal stability.

Since polymer blends have become an economical, effective and versatile way to obtain a wide range of useful polymers with desirable properties, ESO composite has great potential to enhance the protection barrier of the polymeric coating formulations due to the presence of reactive epoxide groups that enable matrices hybrid between those polymers and could be cured by ring-opening reaction of amino or carboxyl groups containing compounds [3,14,30,31]. ESO polymeric composite could serve as an alternative biopolymer protective coating system, as well as, functionalized the polymeric system via innovative formulation due to its process simplicity and the fact that this novel bio-based material is an environmentally friendly and renewable resource.

In the present study, the potential of achieving a complete coating system with fully organic components was investigated by introducing different loading ratios of epoxy and ESO into the acrylic-silicone polymeric blends in order to formulate multiplex organic coating systems. Since organic coatings are characterized by a number of drawbacks that limit their usage in the coating industries, many researches attempt have been made to enhance the performance of such systems [30,[32], [33], [34]].

Apart from the fact that the utilization of inorganic nanomaterials could significantly enhance the overall performance of the polymeric coating systems and give the chance to obtain desired properties for the coated surfaces. The need to develop an entirely organic coating system remains very attractive and essential for developing more eco-friendly coating systems. In that regard, this study reports the development of a multiplex organic coating system that applied with single layer on cold rolled mild steel substrates with ambient temperature curability. The remarkable thermal, physical and mechanical properties, the superior barrier effect and the intact corrosion protection performance, as well as, the enhanced overall performance were confirmed by investigating the chemical structure, wettability, transparency, physico-mechanical properties, thermal stability and the electrochemical responses of all developed coating systems.

Section snippets

Materials

Acrylic polyol resin, denoted as (A), with 2.95 % OH content and 70 % solid content in butyl acetate was used as the base resin and has been supplied by Synthese Malaysia Sdn. Bhd (Malaysia). Silicone intermediate resin (silanol functional phenyl) in the form of solid flake, denoted as (S), with 3–4.5 % OH content was purchased from Wacker Silicone (Germany) and was employed as the modifier resin. Epoxy resin, denoted as (E), with an equivalent weight of 450–500 and viscosity in the range of

Fourier transform infrared spectroscopy (FTIR)

The chemical structure and the cross-linking status among acrylic resin, silicone resin and NCO curing agent were already discussed in our previous paper which confirmed the achievement of the desirable curing level for the coating system at the ambient curing conditions [37]. FTIR was adapted to study the effects of modifying the acrylic - silicone polymeric matrix, with different loading ratios of E and ESO, on the crosslinked structure and the curing quality of the fabricated coating films.

Conclusions

Various loading ratios of E and ESO were utilized to enhance the overall performance of the acrylic-silicone polymeric matrix. The proper crosslinked structure among all the organic components was confirmed by FTIR results with optimum curing level recorded for ES 1 coating system where both chemical and physical interactions were involved. Even though modifying the hybrid polymeric matrix with E and ESO did not result in hydrophobic coated surfaces, the wettability of the coating systems

Author statement

S. Ammar

Prepared the samples, carried out the experiment and wrote the manuscript.

A. W. M. Iling

Characterization of the samples and analysis

K. Ramesh

Design the experiment, analysis of results, correction of manuscript and guided throughout the work.

S. Ramesh

Guided throughout the experiment. Correction of the manuscript.

Acknowledgement

Authors would like to thank University of Malaya for the grant IIRG007C-19IISS. We also thank Ministry of Higher Education for providing Fundamental Research Grant (FP036-2018A).

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