Aging Effects on Natural Fiber-Reinforced Polymer Composites

Environmental concerns have impacted the global scenario, particularly with respect to the use of plastics and their byproducts for real time applications. In this lieu, there is a need for development of bioplastics and bio composites. Thus, the bio composites can be an effective alternative to the traditional plastics to reduce the carbon footprint and to facilitate a sustainable product for enhanced performance and better service conditions. In this regard, this chapter aims at expanding the scientific knowledge on the bio composites and their response under different aging environments. In this chapter, detailed information on the aging mechanism, modes of aging and the methodologies to improve the durability and performance of the bio composites are discussed thoroughly. Specific impetus has been put on the future perspectives and the need for new techniques in aging studies of biopolymers. Further, the pros and cons with respect to the aging of these biopolymers and bio composites can be helpful for researchers.

Recent experimentations witnessed natural fibers as a strong alternative reinforcing element for the synthetic fibers due to their biodegradable and ecofriendly nature. Yet natural fibers are characterized by an inherent disadvantage of poor bonding at the interface of fiber and matrix with that of matrix material which renders substandard mechanical and physical properties of the natural fiber composites. Moisture absorption behavior of the natural fibers is one another demerits of using the natural fibers, since this behaviour may pose the natural fibers to absorb moisture from the surrounding environment owing to their hydrophilic nature. Surface modification renders solution to this problem also by making the surface modified natural fiber to be hydrophobic. Various treatment methods of the natural fibers and its reinforcement in polymeric matrices were dealt in detail in the current chapter. Alongside, the effect of moisture absorption of the natural fibers upon the mechanical and physical properties of the natural fiber reinforced composite materials are also discussed. It was observed from different studies that various characteristics like force of adhesion at the interfacial region between the natural fiber and the polymeric matrix enhanced due to surface modification since the surface area of contact increases which in turn enhanced the mechanical behaviour of the composites and minimized the moisture absorption of the natural fiber composites.

The study on the effect of water aging gives information on the performance of composites at diverse operational conditions. The natural fibers absorb water/moisture and hence the addition of natural fibers in the polymer matrix caused an increase in water/moisture uptake at different environmental operational conditions. This literature survey presented the effect of water aging on the tensile, flexural, fracture toughness, and impact properties of the biocomposites. The mechanical properties of the natural fiber-reinforced biocomposites are reported to drop with water aging. This is caused by the degradation of the fiber/polymer interface due to water hydrolysis. The chemical, physical, and hybridization methods can be adapted to reduce the water uptake of natural fiber-reinforced biocomposites.

Natural fiber-reinforced composites have received significant attention in recent years due to their distinct properties which include reduced carbon dioxide emission, lightweight, reduced tool wear, etc. This chapter provides an outline of the influence of different compatibilizers on the aging characteristics and degradation mechanisms of the natural fiber reinforced thermoplastic composites. Different compatibilization techniques and their effect on various properties which include mechanical, thermal, hygrothermal, chemical has been discussed. It was found that the Compatibilizers play a major role in improving interfacial characteristics and their performance will be decided by the miscibility of its components. The severity of degradation under hygrothermal aging will be lower for composites with compatibilizers and helps in retaining mechanical and thermal properties.

The need for bio-based composites or biocomposites has been increasing over recent years as a measure for sustainable development and to minimize the use of petrochemical-based plastics to reduce global warming. However, the properties of biocomposites are hugely influenced by the environmental parameters because of their inherent material properties. Therefore, in this chapter, the coupled effect of temperature and moisture on the overall mechanical properties of biocomposites is discussed under the framework of hygrothermal ageing. The variation in the parameters of hygrothermal ageing such as the relative humidity, temperature, and ageing time have different effects based on the type of composite, its composition, and the properties of the constituent materials of the composites. These variables may either enhance or deteriorate the properties of such composites. This chapter aims to provide a consolidated understanding of the effects of these variables on the mechanical properties of the biocomposites such as the tensile strength, compressive strength and modulus, flexural rigidity, impact toughness, dynamical mechanical properties such as the storage modulus, loss modulus and the damping coefficient, fatigue properties, shear properties, and many others. The sections in this chapter are designed to discuss the effects of hygrothermal parameters on the said properties exclusively. Additionally, care has been exercised to include biocomposites used in a wide variety of applications including those used in tissue engineering, aerospace components, automobile components, structural components, and many others.

Employing of biodegradable polymers and reinforcements for the development of composites is important for the reduction of environmental problems of non-biodegradable and petro-based polymers. Completely biodegradable composites (biocomposites, ecocomposites or green composites) are composed of natural fibers and natural matrices or synthetic biodegradable matrices. Completely biodegradable composites can replace synthetic fiber based composites due to excellent mechanical properties, low cost and low density. However, biodegradable composites have hydrophilic nature thus, tend to absorb a significant amount of moisture. Mechanical properties of biodegradable composites immersed in water degrade over time limiting the potential applications of these materials. Not only mechanical properties of biodegradable composites but also dimensions of biodegradable composites are affected by water content. Therefore, in this chapter, the works about processing, applications and water aging of completely biodegradable polymer composites were presented. Also, the results derived from literature studies after water aging of completely biodegradable polymer composites were stated.

In the last decade, the environmental issues and cost productions were the effective factors, which increased the rate of replacing the bio-composites with the conventional composites like glass fibers/epoxy composites in the various applications especially secondary or tertiary applications. The bio-composites should be proper capability for maintaining their initial mechanical properties under the various work environments. One of the harsh work conditions is the environment with the high humidity and temperature, which is introduced as hygrothermal environment. Being in this environment under the various dynamic and static loading can age the bio-composites. The hygrothermal aging can influence on the mechanical performance of bio-composites, which can increase or reduce the mechanical properties of those. Characterizing and recognizing the effective factors under the hygrothermal aging can help to the producer or researchers to fabricate the proper bio-composites for using in the hygrothermal conditions. The aim of this chapter is to introduce some of the recognized mechanisms under hygrothermal aging and the effect of them on the mechanical properties of various bio-composites.

Bio-composite materials, which are a serious alternative to synthetic-based fibre and matrix materials due to their high characteristics and biodegradability, cause difficulties and uncertainties for usage conditions due to their high sensitivity to climatic conditions. Scientific studies have shown that climatic factors such as temperature, humidity, radiation, UV rays, and acid rain that act synergistically in natural weathering conditions, cause degradation and changes in the bio-composite material's characteristics. Examining the material's behaviour under natural weathering conditions provides the most realistic and reliable results in terms of determining the shelf life of the material and knowing its behaviour in the usage environment. In this study, changes in thermal, mechanical, and aesthetic properties of bio-composite materials exposed to natural ventilation conditions were investigated. It has been observed that natural weathering induces dramatic decreases in thermal and mechanical properties of bio-composite materials, especially with the effect of prolonged exposure times, and causes changes in colour, surface deterioration and changes in shape.

Bio-composites are promising materials to be used as an alternative to composites. Weathering studies can evaluate the effects of the degradation on bio-composites properties. By accelerated weathering testing, it is possible to predict the durability of materials in a short time. Exposure to UV radiation, moisture, and temperature can cause leading to loss of color and brightness, roughness, and aging of bio-composites. The chemical characteristics, crystallinity, and molecular weight of bio-composites are also affected, with the possibility of randomly break down the polymer chains. The reduction in tensile and flexural strength and thermal properties are also consequences of the degradation process. In this way, to solve this problem, the reinforcement of bio-composites has been investigated. Therefore, this chapter addresses the main environmental factors involved in accelerated weathering and the degradation effects on morphology, molecular characteristics, and thermal and mechanical properties of bio-composites caused by this testing. The influence of nanofillers on the degradation rate of composites are also mentioned.

The emergence of biodegradable plastics as the polymer matrix for natural fibre composites has been rapid, due to the concerns over the accumulation of nondegradable plastic waste in the environment. Given the market growth in exterior applications, there is a need to understand the behaviour of these emerging materials under natural weathering conditions before these materials can be commercialised. In this chapter, we have provided an overview of the natural weathering behaviour of representative completely biodegradable composites. The effects of natural weathering on completely biodegradable composites are no far different from those on natural fibre composites with conventional non-degradable matrices. Any influence of biodegradation from the biopolymer matrices was not evident under natural weathering conditions for at least 2 years. Physical and mechanical deteriorations of the composites were observed after a few months of exposure, the severity depending predominantly on the fibre content. Overall, the conclusion is that the accessibility of the natural fibres and the rate of moisture ingress into the bulk matrix controls the stability of the biodegradable composites upon natural weathering.

The natural fiber-reinforced composites (NFCs) are used to make sustainable eco-friendly products with properties comparable to synthetic materials. However, NFCs are susceptible to aging-induced degradation in environmental conditions such as moisture and ultra violet (UV) exposure. Therefore, it is imperative to understand the aging phenomenon of NFCs and the mechanical properties degradation due to aging and UV exposure. This chapter provides an insight into the effects of aging and UV exposure on the mechanical properties of NFCs. The chapter consists of a comprehensive literature review, simplified procedure for aging and UV exposure tests, a case study and a finite element method (FEM) based model for studying the effect of aging and UV exposure on NFCs. It was evident that with an increase in UV exposure time, the mechanical properties deteriorate significantly as a result of matrix erosion, cracking, and photo-degradation. A further insight into the previous work of one of the authors was provided to understand aging in wood-plastic composites (WPCs). The wood-plastic composites (WPCs) experience a noticeable reduction in the tensile strength (TS), bending strength (BS) and wear resistance after weathering for 13 weeks. In the present work, the sugarcane dry leaves composites (SDLRPCs) also showed a reduction in the TS, BS, and Mode I plane strain fracture toughness (K_1C) after 80 h of UV exposure. The FEM-based micromechanical model was constituted to visualize the state of stress within the NFCs. It predicted that after UV exposure, the NFCs such as SDLRPCs have a higher tendency to undergo matrix shear yielding near the crack tip.

In last few decades, the manufacturing and application of natural fiber reinforced polymeric composites have remarkable achievements to replace the non-bidegradable petroleum based materials. The demand for natural composites is drastically increasing, and became a notable material to use for extensive range of applications such as automotive, aviation, consumer products, and civil engineering, etc. Many investigations and studies have been reported to expand the mechanical and durability performance of biocomposites to compete with conventional composites. Comparatively enormous number of failure mechanisms occurs in fibre reinforced composite arises, and the fatigue life distributions of composites at various constant stress levels are determined using various models. In this chapter, the different methodologies adapted to determine the fatigue life of biocomposites were discussed. The fatigue behavior of biocomposites when subjected to different aging mechanisms under various service conditions and environments were reviewed. Further the chapter also detailed the long-term durability of biocomposites in different dynamic and static stresses under various environments namely corrosive stresses, mechanical stresses, electric stress, thermal stress and photo stress.

Composites are having a massive and extraordinary impact on modern society. Composite manufacturing has witnessed a considerable growth in several areas, including aerospace, structural, and vehicle manufacture. Fibre reinforced polymer composites have become popular throughout the last decade. More recently, researchers have begun paying attention to natural fibre reinforced polymer composites and bio-composites, which are both sustainable and mechanical comparable to synthetics. Also is not only vital in sectors like aircraft and autos, but it becomes critical in civil and structural sectors. This chapter might be useful when it comes to discussing the moisture absorption parameter and qualities for bio-composites. bamboo-based, flax-based, and others bio composites are examined in this chapter. The chapter also describes the impact of moisture content on bio-composites, parameters influencing the effectiveness of moisture absorption treatments used for natural composites, treatment of composites of natural origin, water absorption behaviour, and its effect on mechanical properties of natural fibre reinforced composites. Also, the chapter highlights the environmental impact on the durability and mechanical performance of bio-composites.

The reduction of synthetic fibre usage in the various industries has grabbed attention of the researchers towards natural fibres. Since petroleum-based polymers and fibres are harming eco-system constantly by exhausting poisonous gases. Natural fibres are considered to be a potential replacement of synthetic fibres by means of eco-friendly, bio-degradability, recyclability, sustainability and innumerable other unique characteristics. It directly contributes towards circular economy of the local market. Hydrophilic nature plays vital role in impacting performance of the natural fibre, hence it becomes a sensitive towards humidity in working condition of the fabricated parts. The parts reinforced with natural fibre are subjected to hygrothermal ageing which directly influence the physical and chemical characteristics. The diffusion coefficient a property which defines the rate at which water molecules diffuses through material. By using Arrhenius equation and Fickian model optimize the modelling of a hygrothermal ageing of natural fibre reinforced polymer composites.

Nanocomposites are suitable for advanced engineering applications, i.e., automotive, aeronautics, biomedical applications, catalysts, gas-separation membranes, contact lenses, bioactive implant materials, bone applications, and food packaging due to their higher mechanical and thermal resistance properties. Environmental friendly natural fibre-based bionanocomposites are important because of their renewable, biodegradable and compostable nature. Natural fibers both in nano, i.e., cellulose nanocrystal (CNC), microfibrallated cellulose (MFC), microcrystalline (MCC), and macro-sized, i.e., carboxymethyl cellulose (CMC) are used to produce bionanocomposites together with bio or synthetic polymers, i.e., starch, polyurethane (PU), polylactic acid (PLA), using different methods. These composites have already proved to be invaluable gifts to the present and future generations in many different aspects, and thus, thanks go to the modern science and technology. However, in the same way as other composites the physical and mechanical properties are affected severely by different aging conditions like pressure, temperature, humidity and the curing condition. The absorption of water and plasticization of the composites deteriorates the service life, increases the chain mobility and decreases the glass transition temperature. It also reduces the mechanical properties of the composites. Thus, researchers are working on the effect of different aggressive environments on the durability of composites and to understand the changes in the physical and mechanical properties over the period of aging. This chapter deals with the different environmental aging conditions and their impact on the properties of the composites.

Natural fiber-based hybrid composites have received the attention of many researchers for their excellent mechanical properties. However, moisture absorption into the hybrid composites affects the properties during their application. Hemicellulose and cellulose of the fiber are mainly accountable to moisture absorption. This chapter discusses the effects of moisture absorption on the mechanical and physical properties of natural fiber-based hybrid composites. Physical properties such as dimensional instability and glass transition temperature (T_g), and mechanical properties (tensile, flexural, fracture, and impact) decrease when the natural fibers absorb the moisture. This is predominantly owing to the reduction in interfacial bonding between the fiber and the matrix. Since water molecules works like a plasticizer, strain to failure decreases, and strain energy release increases. Understanding the moisture absorption of hybrid composites can give insight into increasing their durability and performance.

This chapter discusses the aging effects (e.g., photochemical, hydrothermal, natural, thermal, freeze–thaw cycling, and xenon-arc light) on various mechanical characteristics of biocomposites with the recycled polymer. In general, biocomposites show a decrease in tensile strength after photochemical aging, but tensile modulus and strain to failure do not vary significantly with increasing aging time. In contrast, tensile modulus and ultimate tensile strength of biocomposites reduce significantly with hydrothermal aging, but the strain to failure increases. Also, flexural modulus, tensile modulus, tensile strength at break, and elongation at break increase after natural aging. Furthermore, there is an increased tensile modulus and strength of biocomposite under accelerated thermal aging. The process and result of aging depend on the type of biocomposites. As the use of biocomposites is widely increasing, this chapter can be useful for getting insight into the durability performance of the biocomposite materials.

Due to the sustainable, and commercial outcomes of the natural fibers, along with their desired features such as high specific mechanical properties, natural fiber-reinforced composites (NFRCs) are exhibiting a strong potential to be employed in different applications such as aerospace, automotive, packaging, etc. This chapter presents a comprehensive discussion on the main characteristics of seawater ageing and moisture ingress mechanism influencing natural fibers and their performance as reinforcement in polymer matrix composites. This chapter presents the influence of seawater ageing on the physical and mechanical properties of NFRCs. Furthermore, the chapter also discuss various measures to prevent moisture ingress. Many researchers have been focusing attention to overcome the issues due to moisture absorption, with particular interest paid to the physical and chemical treatment of reinforcements and improving the fibre–matrix interface strength. Recent studies and developments dealing with moisture repellent coatings are also discussed.