Hygrothermal and Mechanical Performance of Carbon Nanotube–Natural Fiber Hybrid Composites: A Comprehensive Theoretical and Critical Study

Abstract

Background: Hybrid composites that combine carbonaceous nanofillers such as carbon nanotubes (CNTs) with natural fibers have attracted significant interest for structural and multifunctional applications because they promise the stiffness and multifunctionality of nanocarbon reinforcements alongside the low density, sustainability, and toughness benefits of natural fibers (Balasubramanian and Burghard, 2005; Santulli, 2019). However, the behavior of these hybrid systems under combined environmental stressors — particularly moisture uptake and hygrothermal cycling — and the corresponding effects on viscoelasticity, creep, interfacial stress transfer, and damage evolution remain incompletely understood. Moisture interacts with polymer matrices, fiber surfaces, and nanoscale interfaces in ways that can produce reversible and irreversible changes in mechanical performance (Ferguson and Qu, 2006; Zhang and Wang, 2006; Athijayamani et al., 2009).

Objectives: This article synthesizes the theoretical frameworks and empirical findings relevant to the hygrothermal response and mechanical performance of CNT–natural fiber hybrid composites. It aims to (1) elucidate the mechanisms by which moisture and temperature influence matrix, fiber, and interface

behavior; (2) integrate knowledge on time-dependent phenomena such as creep and viscoelastic damping in the presence of nanocarbon fillers and natural fibers; (3) identify principal modeling approaches and experimental strategies to assess durability; and (4) propose a structured research methodology and interpretive framework for future high-fidelity experimental and computational studies.

Methods: The work undertakes an exhaustive theoretical elaboration, drawing on nanoscale functionalization studies for CNTs, experimental investigations into hygrothermal effects on carbon-fiber and natural-fiber composites, and research on creep and damping in polymer and nanocomposite systems (Balasubramanian and Burghard, 2005; Yizhuo et al., 2014; Jia et al., 2011; Tehrani et al., 2011). Mechanistic paths are delineated using continuum and multiscale reasoning — from molecular interactions at functionalized CNT surfaces to macroscopic composite constitutive responses — and critical analysis is applied to reconcile apparently conflicting empirical observations. The Methods section describes rigorous, purely textual experimental protocols and modeling pathways that would form a robust research program.

Results: A composite of theoretically derived outcomes indicates that: (a) chemically functionalized CNTs alter local hydrophilicity/hydrophobicity and interfacial energy landscapes, influencing water diffusion pathways and stress transfer (Balasubramanian and Burghard, 2005); (b) moisture-induced plasticization and hydrolysis in typical thermoset and thermoplastic matrices lead to a complex interplay of reversible softening and irreversible matrix degradation that scales with exposure time, temperature, and fiber/matrix chemistry (Ferguson and Qu, 2006; Jen and Huang, 2013); (c) natural fibers impart additional moisture sensitivity through capillarity and bound water within cellulosic microstructures, leading to swelling-driven internal stresses that can degrade fiber–matrix bonding (Athijayamani et al., 2009; Sarkar et al., 2010); and (d) CNTs can either mitigate or exacerbate hygrothermal damage depending on functionalization, dispersion, and interfacial coupling strategies (Zhang and Wang, 2006; Tehrani et al., 2011). Time-dependent behaviors such as creep and damping are highly sensitive to moisture content and interfacial integrity; nano-reinforcement tends to raise stiffness and retard creep at low to moderate moisture contents but may accelerate localized stress concentrations and crack nucleation under severe hygrothermal exposure (Jia et al., 2011; Yao et al., 2013).

Conclusions: The hybridization of CNTs and natural fibers offers pathways to design composites with tunable hygro-mechanical performance, but realizing reliable, durable materials demands integrated approaches that combine chemical engineering of interfaces, precise control of microstructure, and multiscale predictive modeling. Continued experimental efforts using standardized hygrothermal protocols and advanced nanoscale characterization, coupled with constitutive models that include moisture-dependent viscoelasticity and interfacial debonding, are essential to translate laboratory promise into engineering practice (Mulenga et al., 2021; Alhijazi et al., 2020). This article provides a detailed conceptual and methodological roadmap for such research.