Current Approaches on Natural Fiber Reinforcement Surface Treatment for Construction Material Application

Natural fiber-reinforced polymer composites are presently receiving the attention of scholars and industrialists due to their specific properties, such as being naturally eco-friendly, biodegradable, economical, viable, available, and sustainable. The key problems associated with natural fiber polymer composites, including fiber/matrix compatibility, high moisture absorption, and, especially, thermal degradation in engineering plastics (high-temperature plastics), constitute the most critical thrust of this review. It is noted that at high temperatures, natural fibers degrade and this has adversely restricted their usage with only commodity thermoplastics having relatively low melting temperatures, such as polypropylene (PP) and polyethylene (PE). This review paper, therefore, provides valuable research highlights on utilizing and improving the mechanical and thermal properties of natural kenaf fibers as reinforcement in engineering polymer composites for high-temperature engineering applications using polymer matrices, such as polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), and polyphenylene ether (PPE). The initial and various chemical treatments of natural fibers, their effect on the thermal and performance properties of natural fiber engineering thermoplastic composites, and the advanced treatment of epoxy coatings are reviewed. Applications of natural fiber-reinforced thermoplastic composites in the construction and automotive industries, as well as in other applications, are outlined. It was established that the adhesion and thermal stabilities between polymer matrix and natural fibers are better improved by surface coating with diluted epoxy resin thermoset. This eventually improved the overall thermal and performance properties of the resultant composites and will serve as a data bank and guide for manufacturers and future research directions using high-end engineering polymers with higher processing temperatures.

Abstract. Nowadays, the management of agricultural waste is a major challenge for authorities and its burning is still uncontrolled that causes severe health issues. In other hand, shortfall in conventional wood awakened researchers to fabricate new composite variants such as natural fiber reinforced polymer composites. However, the use of natural fibers could not incur sufficient mechanical and thermal strengths in the composites. In this work, to demonstrate the sustainable change in thermal and mechanical properties in composites by chemical treatment; alkali treatments of the rice straw and husk are carried out. Hybrid-composite specimens are manufactured by hand layup process, mechanical (hardness, impact, tensile, and flexural) and thermal tests (TGA/DTG, flammability, and thermal absorption) are conducted. Comparative studies show that about a 30-40% rise in mechanical strength and thermal stability is achieved by alkali treatment advocated by SEM finding that shows alkali treatment enables superior fibre-matrix bonding.

Fiber reinforced polymer composites (FRPCs), due to their multifunctional properties, have already occupied a significant place in various applications such as aerospace, automotive, marine, structural engineering, and healthcare industries. Lightweight FRPCs are preferred over heavier materials because of some key advantages, such as high strength-to-weight ratio, corrosion resistance, design flexibility, fatigue resistance, damping properties, and electrical and thermal insulation properties. Though synthetic fibers such as carbon, glass, aramid fiber reinforced composites are found to provide better performance, these fibers are expensive as well as impose adverse impacts on the environment. Currently, bast fiber reinforced biocomposites (BFBCs) are receiving increasing attention due to their biodegradability, availability, low cost, and higher strength-to-weight ratio. Researchers are working rigorously on BFBCs to unveil their optimal properties. BFBCs can be disposed of easily without affecting the environment. BFBCs, with their sustainable and biodegradable properties, notably promote the use of natural fibers particularly bast fibers and minimize the consumption of expensive and non-degradable synthetic fibers reinforcements in the composite industry. This paper provides an overview of the use of different natural fibers in reinforcing polymer composites for various applications to achieve sustainability. The influence of various fibrous preforms of bast fibers on the mechanical behavior of BFBCs, and their prospects are comprehensively reviewed.

The relatively high cost of man-made fibers and wire meshes used in fiber reinforced concrete and ferrocement, combined with a reduction in the usage of asbestos fibers, make it necessary to evaluate natural fibers as possible substitutes. This is particularly true in some low-cost housing applications, such as those used in Mexico, where the cost of the reinforcement represents a major portion of the total cost. Some natural fibers of the agave family, which are widely available in Mexico, show surprisingly high mechanical properties; yet little effort has been devoted so far to using them efficiently. This paper describes the results of a cooperative research project to study the use of natural agave fibers as possible reinforcement for portland cement-based matrixes. The following questions are answered: I) What are the essential mechanical properties of these fibers? 2) What are the difficulties encountered in mixing them with a mortar matrix? 3) What are the optimum and practical maximum amounts of fibers that can be mixed? 4) Can a composite showing an elasto-plastic behavior (or better) under loading accompanied by multiple cracking be obtained? 5) Does the composite have a fairly good durability under various environmental exposures? The results so far are very encouraging and necessitate further systematic research in the use of natural fibers.

The interest in the use of natural fibres with polymeric matrix for the preparation of composite spread rapidly over the last years. However, the interfacial adhesion between the fiber and the matrix has to be improved. To improve the adhesion between the constituents and consequently the mechanical and thermal properties of materials, two approaches were investigated: electron beam irradiation and mercerization. This paper describes the fabrication and characterization of biocomposites compounds with high density polyethylene and fibre from Brazil nut pod that were prepared by two different methods: the first irradiating the composite with 150 kGy and the second was radiating matrix with 15 kGy and then produce the composite. For both methodologies, natural fibers, mercerized and nonmercerized were used. The effect of the treatments to improve adhesion between the fiber and the polymer matrix was evaluated through mechanical, chemical, thermal and morphology charcterization. Based on this study, it was observed that fibre from Brazil nut pod is a technically viable material for use as reinforcement in polymer composites. It was observed that the process of matrix irradiation followed by the composite fabrication is an effective method for improving the thermal and mechanical properties of the composites, when compared with mercerization process, this method can be considered more environmentally friendly (no chemicals, and without generating waste), cheaper and simpler.

<p><strong>Introduction: </strong>Recycling and reuse of the polymer composites have been gaining popularity these days due to their environmental and disposable concerns. However, the recyclability of natural fiber and fly ash reinforced polymer composite is still not explored much which has restrained the industries not to use them at full potential. Recycling of polymers, polymeric composites, and their wastes are trending nowadays. Researchers have used both recycled reinforcements such as paper, fiber, etc., with matrix and fresh reinforcement with recycled matrix too. In this regard, limited reports have been found on the recycling of the natural fiber reinforced polymer composites. In spite of this, when it comes to the recycling of degradable materials, it is still in the nascent phase. Recycling of the biodegradable materials may lose some of their original properties after every cycle (1). These lost tensile and flexural properties may be exhibited due to the fiber breakage, fiber degradation, change in fiber aspect ratio, and polymer chain shortening. Reinforcement of the recycled composites with fresh fibers to restore their lost tensile and flexural properties could open a new window for the researchers. Current work focuses on the recycling and subsequent reinforcement of the recycled composites to enhance the tensile and flexural properties of the same.</p> <p><strong>Methods:</strong> Hybrid composites with 15-30 wt.% sisal fibers and 5-15 wt.% fly ash were formulated with impact modified polypropylene. The impact on mechanical properties due to the recycling and reinforcement was investigated. All the tensile, flexural, and impact testing samples have been fabricated by using Hakke rheomix and Hakke Minijet II micro injection molding machine (2).</p> <p><strong>Results & Discussion: </strong>Composite with 15 wt.% sisal fibers showed a minimal ~2 % and ~2 % loss in tensile and flexural strength while the one with 30 wt.% fiber showed a maximum ~10 % and ~4 % loss respectively. In order to restore the lost mechanical properties, recycled composite have been reinforced with 5 wt.% natural fiber. The establishment of a good interfacial adhesion between reinforcing filler and fiber has been confirmed from FTIR studies. Strong interfacial interaction among reinforced SSL fiber and the blended matrix leads to a strong polymer composite. Although there is a decrease in tensile and flexural properties of the hybrid composite due to the increased reinforcement of fly ash, these are the still close to the base matrix. Also, an improvement in notched impact strength of the composite has been observed (3). Recycled, polymer composite samples show that the hybrid composites with highest fly ash content show the least decrease in tensile and flexural properties due to the non-breakage of fly ash particles. However, an insignificant change was, observed in impact strength of the recycled and reinforced composites.</p> <p><strong>Conclusions: </strong>Recycling and reinforcement with 5 wt.% of FA of hybrid PP composites consisting of sisal fiber and fly-ash were successfully completed and evaluated. Fly ash plays a vital role in restricting the damage to the mechanical properties due to the recycling. Furthermore, inclusion of 5 wt.% of SSL fiber to the recycled composites sample helped in reclaiming lost mechanical properties.</p> <p><strong>Keywords:  </strong><em>Composite Recycling, Hybrid composite, Natural fiber, Fly ash</em></p> <p><strong>References</strong></p> <p>1.   Lila MK, Singhal A, Banwait SS, Singh I. A recyclability study of bagasse fiber reinforced polypropylene composites. Polym Degrad Stab. 2018 Jun 1;152:272–9.</p> <p>2.   Maurya AK, Gogoi R, Manik G. Study of the Moisture Mitigation and Toughening Effect of Fly‐ash Particles on Sisal Fiber‐Reinforced Hybrid Polypropylene Composites. J Polym Environ [Internet]. 2021 Jan 21 [cited 2021 May 7];1–16. Available from: https://doi.org/10.1007/s10924-021-02043-3</p> <p>3.   Kulkarni MB, Radhakrishnan S, Samarth N, Mahanwar PA. Structure, mechanical and thermal properties of polypropylene based hybrid composites with banana fiber and fly ash. Mater Res Express [Internet]. 2019 Apr 5 [cited 2020 Oct 26];6(7):075318. Available from: https://doi.org/10.1088/2053-1591/ab12a3</p>

The current industrial method of extracting natural plant fibers, originally intended for their textile use, can degrade the inherent mechanical properties, making them difficult to replace e-glass fibers for reinforcement in polymer composites. Microorganisms during the initial dew/field retting step of fiber extraction process not only degrades the fiber-stem interphase bond constituting primarily pectin and lignin, but also degrades the structural components of the fiber such as cellulose, resulting in non-uniform technical fibers with poor mechanical properties. Also, current single fiber testing standards used for mechanical properties characterization of these fibers are suitable for assessing homogenous and uniform fiber properties correctly, which is not the case in natural fibers. In this study, the flax stems were treated with Pectinase Ultra SPL enzyme targeted to degrade the pectin bonds between the fibers and plant stem, without affecting the structural component cellulose. In this study, the size of technical fibers hand extracted from dew and enzyme retted flax are compared. The hand extracted enzyme retted stem fibers showed more uniform, finer diameters resulting in better tensile properties when compared with dew/field retted stem fibers. The improved properties are related to the diameter effect in which as the area of these fibers is reduced, the reduction of defects during the fiber extraction.

The present review article provides an overview of the properties of various natural and synthetic fibers for the fabrication of pure natural composites and the combination of both natural/synthetic fibers-based hybrid composites, bio-based resins, various fabrication techniques, chemical and mechanical properties of fibers, the effect of chemical treatment and the influence of nanoparticles on the composite materials. Natural fibers are becoming more popular and attractive to researchers, with satisfactory results, due to their availability, ease of fabrication, cost-effectiveness, biodegradable nature and being environmentally friendly. Hybrid composites made up of two different natural fibers under the same matrix material are more popular than a combination of natural and synthetic fibers. Recent studies relevant to natural fiber hybrid composites have stated that, due to their biodegradability and the strength of individual fibers causing an impact on mechanical properties, flame retardancy and moisture absorption, natural fibers need an additional treatment like chemical treatment for the fibers to overcome those drawbacks and to enhance their better properties. The result of chemical treatment on composite material properties such as thermal, mechanical and moisture properties was studied. Researchers found that the positive influence on overall strength by placing the filler materials (nanoparticles) in the composite materials. Hybrid composites are one of the fields in polymer science that are attracting consideration for various lightweight applications in a wide range of industries such as automobile, construction, shipping, aviation, sports equipment, electronics, hardware and biomedical sectors.

It is necessary to analyze the manufacturing process of recycled natural fiber reinforced polymers to produce polymer composites that are successful in the manufacturing process. This discussion begins with the manufacturing process of natural fiber reinforced recycled polymers. The outline of this article refers to the manufacturing process, manufacturing process constraints, and the appropriate methods of the manufacturing process. The literature review describes the manufacturing process of natural fiber reinforced recycled polymers with the constraints encountered during the manufacturing process by investigating suitable methods of treating natural fibers for success in the manufacturing process of natural fiber reinforced recycled polymers. The five-step systematic literature review (SLR) was chosen as the approach in reviewing the literature. The analysis of selected articles reveals that the successful manufacturing process of natural fiber reinforced recycled polymers is the treatment of natural fibers, followed by a manufacturing process that matches the polymer manufacturing needs. Treatment of natural fibers using alkaline treatments (sodium hydroxide (NaOH) and stearic acid ((CH3(CH2)16COOH)) is the most influential factor in the success of the manufacturing process of recycled natural fiber reinforced polymer composites.

A Kenaf composite was prepared by using hand lay-up process. The effect of weather on mechanical, morphology and thermal properties of kenaf composite were studied. Tensile strength of kenaf compositewas found to be 60MPa. Unfortunately, tensile strength of thecomposite starts to decrease after the first weathering month through to the weathering periods with constant reduction of tensile, at the end of the wreathing period., almost 85% the composite mechanical behaviour is lost. From the mechanical properties result obtained it clearly seen that natural fiber and their composites are not able to stand environmental condition because they have poor wettability, incompatibility with some polymeric matrices and high moisture absorption. Due to the high moisture absorption properties, there are formations of void in interfacial adhesion between fiber and matrix which can reduce the mechanical properties of composite such as flexural strength or flexural modulus this clearly supported by SEM results. Fortunately some modification can do towards improving the mechanical properties and it is good enough to achieve the high performance of the composite with proper system formulation during the modification processand the result of reinforced kenaffiber will be presented in our next publication.

Natural fiber has been widely used as reinforcement in polymer composites, and the excellent sound insulation and lower mechanical properties of natural fiber increased research interest in hybrid fiber-reinforced composites. The mechanical and sound insulation properties of hybrid composites reinforced with natural fiber and carbon fiber are important for applications in aircraft and automobiles. In this study, hybrid composites reinforced with a core–shell structure composed of sisal and carbon fiber were developed, the composites were fabricated by vacuum aided resin infusion molding (VARIM) process, and different molding pressure was used to vary the compaction degree of sisal fiber in the composites. The mechanical and sound insulation properties of the composites were studied, and the mechanism of sound insulation and interface properties between continuous sisal fiber and carbon fiber were discussed. The results obtained show that with the decrease in molding pressure, the mechanical properties of laminates decrease and the sound insulation properties increase in stages. The sound insulation property of the composite is attributed to surface dissipation, internal scattering and sisal fiber hollow insulation.

The ecological conservation in the current global scenario has led scholars to use natural fibers as a reinforcement in composites that resulted in the exploration of new natural cellulose fibers. This research investigates the extraction and characterization of natural cellulose fibers from the stems of Buxus sempervirens (BS) plants, which are used to produce various products. Manual retting of stems resulted in Buxus sempervirens fibers production, which was then evaluated for their physical, chemical, thermal, crystallographic, and morphological characteristics. The results elucidated that BS fibers had a cellulose percentage of 51.78%, 18.42% hemicellulose, and 17.36% lignin. The Fourier Transform Infrared Spectroscopy results validated the chemical constituents. Crystallographic investigations utilizing X-Ray diffraction revealed a crystalline index of 18.05%. The thermogravimetric analysis of BS fibers showed char residue of 33% and a maximum degradation temperature of 263°C. The BS fibers revealed good surface interlocks that can be inferred from Scanning Electron Microscope. Thus, from the results compared with other natural fibers, we demonstrate that Buxus sempervirens fibers can be effectively used as reinforcement in polymeric composites.

In today's fast-developing world, the use of composite materials is closely related to environmental pollution, renewable and biodegradable resources. A researcher is looking for environmentally friendly materials. Natural and synthetic fibres come in a wide range of shapes and sizes. Natural fibres include jute, straw wheat, rice husk banana fibre, pineapple leaf fibre, cotton, Sisal, Coir, Oats, and Bagasse. Every year, 13.5 tonnes of banana fibre are produced in India. Teabags, paper, and polymer composite reinforcement are just a few of the applications for banana fibre. This article focuses on the manufacture of banana fibre with epoxy and a variety of other natural fibres. By combining banana fibre with some current technology, waste will be reduced, and energy efficiency will be increased, all while supporting sustainability. Banana fibres are covered in this work, along with their uses, applications, and mechanical qualities, as well as how banana fibre might improve mechanical properties.

In recent years, interest in using natural fibers in a number of applications especially in biocomposites has grown because they are eco-friendly, lightweight, combustible, nontoxic, low cost and easy to recycle. On the other hand, the lack of good interfacial adhesion and poor resistance to moisture absorption and chemicals make the use of natural fibers less attractive. Chemical treatment of the lignocellulosic fiber can stop the moisture absorption process, clean the fiber surface, chemically modify the surface or increase the surface roughness. Silane treatment of natural fibers is a promising process for improving physical and chemical properties of fibers. The work presented in this article gives insight into the effect of silane treatment on physical and chemical properties of Pinus fibers. Further polymer composites were prepared using urea-formaldehyde as a novel polymer matrix resin. The silane-treated and untreated fibers along with polymer composites have been characterized by various techniques such as scanning electron microscopy (SEM), Fourier transform-infrared spectrophotometry (FT-IR) and thermogravimetric/differential thermal analysis along with DTG studies. Composites prepared were also subjected to the evaluation of different mechanical, physical, and chemical properties.

A Review on mechanical property of sisal glass fiber reinforced polymer composites