Thermal, mechanical and barrier properties of rice husk ash biosilica toughened epoxy biocomposite coating for structural application
Introduction
The expansion of composite applications is due to several factors, the most important of which is that composite-fabricated items are stronger and lighter. Thus composite materials are predominantly used in many engineering applications nowadays. This changing environment create many new requirements and opportunities, which are only possible with the advances in novel materials and their corresponding production technologies [1]. Nowadays, demand for composite materials with enhanced thermal properties, as well as other qualities such as mechanical performance, a wide operating temperature range, and appropriate chemical resistance to the surroundings, is increasing [2]. Environmental and sustainability concerns have prompt attempts to develop bio-based composite materials for a variety of end-use application areas and as a unique alternative to synthetic composite materials [3]. On the other hand, biocomposite materials are not a problem-free alternative, and they have certain disadvantages such as poor moisture resistance (hydrophilicity), low thermal stability, flammability, poor machining and extremely anisotropic characteristics [4]. There are lot of studies to addresses these issues on long-term durability, dependability, serviceability, characteristics, and sustainable manufacturing (via adopting a circular economy in biocomposites).
To overcome from these issues coating is one of the best options for such materials to make them thermally stable, mechanically tougher, hydrophobic and non-reactive to environmental conditions and different gases. Epoxy resins are adequate materials for structural applications because they have excellent mechanical properties, minimal shrinking while curing, low residual stresses, and excellent heat and chemical resistance [5], [6]. Epoxy resins are available in a broad variety of combinations, making them ideal for numerous applications, including adhesives, coatings, and composite materials [7]. Nonetheless, there is considerable interest in enhancing the performance of epoxy resins in order to impart additional desirable qualities. Epoxy resins, like the majority of polymers, are electrically non-conductive and have low thermal conductivity. A strongly cross-linked network gives epoxy resins their outstanding mechanical characteristics, but it also makes them brittle materials with intermediate fracture toughness when compared to other polymers. There are numerous attempts have been made to address these disadvantages so far [8].
Generally, particles such as Al2O3, SiO2, SiC, Fe2O3, CBN, and B4C are preferred for the production of high-performance polymeric coating systems [9]. However, the use of commercial fillers raises the cost of the product and necessitates stringent process control. Bio-derived ceramics prepared from peanut hull, orange peel, sea urchin, rice husk (biosilica), wheat husk, and clay are widely used as particulate reinforcements in high-temperature composite coatings for a variety of technical uses [10]. These bio-derived micro or nanofillers exhibit qualities comparable to or greater than 80 % of those of synthetic fillers while maintaining a high level of environmental safety and biocompatibility. Generally, these bio-fillers are derived from agricultural wastes associated with food preparation, as well as animal and marine waste. Certain bio-fillers are even derived from plants, fruit peels, and edible products [11]. The use of these fillers has no adverse effect on the environment and changes polymeric goods into biocompatible form. Recycling these agricultural wastes into valuable bioceramics has the potential to significantly reduce the amount of solid waste on the planet, limit environmental damage, boost the process economy as well as support solid waste management [12]. Biosilica has several benefits over other fillers in all bioceramics. Biosilica's desired qualities include high moisture absorption, increased wear resistance, toughening of the polymer matrix, high heat stability, and good time-dependent behavior made it as more suitable reinforcement for many applications. Ariffin et al. [13] examined to enhance the anti-corrosion capabilities of a bio-based polymer epoxy acrylate when it was combined with nano zinc oxide particles. The epoxy acrylate coating was combined with nano zinc oxide to create hybrid nanocomposites that were used to shield a mild steel panel against corrosion. Author reported that the inclusion of a 5 wt% of ZnO loading considerably improved the corrosion resistance and coating performances via EIS.A. V. Similarly, Buketov et al. [14] demonstrated that adding ultra-fine diamond particles at a concentration of 0.05 part by weight per 100 parts of the epoxy binder significantly boosts the bending strength and minimizes residual stresses in the epoxy matrix. Additionally, the elastic modulus also rises in the composite's materials. Optical microscopy was used to analyze the fractured surfaces of nanocomposite materials. The topology of fracture surfaces of nanocomposite materials was analyzed, and it was discovered that the structure is ordered, with no visible inclusions, indicating that the composite materials have reached their maximum degree of cross-linking at a concentration of ultra-disperse diamond of 0.05 pt. wt. Madueke et al. [15] demonstrated an improvement in the mechanical properties of unsaturated polyester filled with snail shell particulates, while Onuegbu et al. [16] demonstrated an enhancement in the mechanical properties of polypropylene filled with various size particles of snails' shell powder. However, sometimes the addition of particles makes the composite material more brittle by particles amalgamation with the creation of the clustering effect. Hence, for improving their adhesion and dispersion on the matrix the silane surface treatment could be done via an aqueous solution method since the method has simple process parameters like no specific temperatures, no specific ambiance, and rapid production of surface-treated reinforcements [17]. Julyes et al. [18] studied the effect of silane surface-treated iron(III) oxide particles in the thermo-mechanical behavior of epoxy resin composite. Their research study explicated that the silane-modified iron(III) oxide particles improved the mechanical and thermal stability of the epoxy composite.
So far very few researchers only investigated the kind of mixing of biosilica into polymer matrix medium as coating material. The utilization of silane treated biosilica derived from rice husk ash (RHA) into the epoxy was researched by a few researchers and the property evaluation in thermal, mechanical and barrier behavior as a coating material is also not much familiarized. Hence the present study aims to investigate the mechanical, thermal, and barrier behavior of surface-modified RHA epoxy biocomposites. The silane treatment could perform by utilizing surface modifier 3- Aminopropyletriethoxysilane and the coating composites could prepare using solution casting process. Further characterizations could perform with respect to the corresponding ASTM standards. Such thermally stable, mechanically strengthened and barrier to environmental effects enriched composite coating material could be used in structural and industrial coating applications.
Section snippets
Materials
The epoxy resin used for this present study was a liquid diglycidyl ether of Bisphenol-A (DGEBA) type (Huntsman India Ltd. Mumbai, Araldite LY556) having a density of 1.18 g/cm3 with an equivalent weight per epoxide group of 195 g/mol at 25 °C. Triethylenetetramine an aliphatic hardener having a density of 0.98 g/cm3 was used as a curing agent. The silane surface modifier 3- Aminopropyletriethoxysilane having a molecular weight of 179.29 g/mol was purchased from Sigma Aldrich, USA. The
Mechanical analysis
The tensile and flexural testing was performed on the composites in accordance with ASTM D-638 and 790, respectively. The tensile specimens are in dog bone shape with a thickness of 3 mm, span length of 33 mm, total width of 19 mm and total length of 115 mm. Similarly, the flexural specimens are in rectangular shape of 63.5 × 12.7x3mm. The test was performed using a universal testing machine (INSTRON 4355, UK) with a cross-head speed of 1.5 mm/min. A Shore-D durometer, blue steel India was used
Mechanical testing
The mechanical properties like tensile, flexural strength, and hardness for various composite designations illustrates in Fig. 3. Composite designation E shows lesser values than all over composite designations, for tensile, flexural strength, and hardness tests around 63 MPa, 92 MPa and 86 shore-D, correspondingly. These lower values are due to the brittle nature of epoxy and the main constituent of composite designation E is plain epoxy only. Furthermore, the addition of silane-treated
Conclusions
In this research, a performance improved epoxy biocomposite coating was prepared using rice hush biomass converted biosilica and characterized for its mechanical, thermal, and barrier properties. The rice husk ash was converted as biosilica via the thermo-chemical method and the silane treatment on biosilica particles was done via the aqueous solution method. Further, the biosilica particles are mixed with resin using an ultrasonicator for making the composite coating material. The specific
Funding
Funding received for this research.
Data availability statement
Data are contained within the article.
Credit author statement
Both the authors equally contributed in this research and manuscript preparation & revision stages.
Declaration of competing interest
There is no conflict and competing of interest between authors on this article.
Acknowledgment
The authors are thankful to the Deanship of Scientific Research at Najran University for funding this work under the Research Collaboration Funding program grant code (NU/RC/SERC/11/4).
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