**3.6 Disadvantages of natural fiber composites**

Biocomposites function and quality majorly relies on biofibre characteristics. On the other hand, when biofibres are used for applications related to building materials, the composites have shown some disadvantages such as possessing high moisture absorption, low modulus elasticity, faster decomposition when surrounded by basic conditions, during microbial encounter, and visible variability in mechanical characteristics. In order to overcome these limitations, natural fibers need to be thoroughly studied to produce better performing fibers in future. Even though biofibers have various advantages for their usage in composites, they do possess certain disadvantages like being incompatible with other matrices, reduced wettability etc. [31, 32]. As mentioned briefly, the physical and chemical characteristics of biofibres are determined by cell wall based polymers and their matrix component (**Table 2**). The major properties of the fibers such as flammability, dimensional stability and biodegradability can be directly altered using external factors such as acids, bases, and UV rays by converting the green composite into carbon dioxide and water [30]. Therefore, to effectively overcome these limitations, there is a requirement to improve biofibre properties through altering the cell wall polymers chemistry [28].

In general, for achieving a decent function of short fiber reinforced polymer composites (SFRP), the content of fiber in the composite should be considerably higher [4]. The tensile characteristics of fiber reinforced is usually affected by occurrence of fiber and other materials used in the matrix [3]. Therefore, researchers are heavily focussed on studying the biofibers used in biocomposites and how they affect it [4].


#### **Table 2.** *Properties of selected natural and manmade fibers [6, 8, 9].*

Natural fibers are generally known to be hydrophilic in nature and the polymer matrix tends to be more on the hydrophobic side. Due to this difference in their polarity, the composite material usually inclines to aggregate. There is increased water absorption as a result of hydrophilic fibers, showing a weak resistance to moisture. This further leads to producing poor tensile property reinforced composites. In addition to the basic cellulose unit, fiber surfaces contain wax coating and non-cellulosic compounds like lignin, pectin, and hemi-cellulose resulting in weak bonding among the biofibers and matrix.

Hydrophilicity being an undesirable property for obtaining natural fiber reinforced composite having good tensile properties, the fiber's hydrophobicity needs to be increased by using surface modifications (surface treatment). The natural fibers are modified for enhancing hydrophobic nature, roughness, interface bonding among the biofibres and matrix, and wettability. The modifications of the fiber also decrease the moisture absorption of the composite which gives us enhanced tensile properties [10, 12, 16, 17, 23].
