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Advances in Natural Fiber Composites and Their Interfacial Adhesion

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Macromolecular Chemistry".

Deadline for manuscript submissions: closed (31 December 2019) | Viewed by 27276

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Special Issue Editors

Dr. Pietro Russo

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Institute for Polymers, Composites and Biomaterials, National Research Council, Via Campi Flegrei 34, 80078 Pozzuoli, NA, Italy
Interests: polymer-based composites; nanocomposites; polymer processing; mechanical properties; rheological behavior
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Fabrizio Sarasini

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Department of Chemical Engineering Materials Environment, University of Rome La Sapienza, 00184 Roma, Italy
Interests: fibre/matrix interfacial modification and assessment; use of plant fibres in biopolymers (biodegradable or from renewable resources) for designing biocomposites with reduced environmental impact; combination of natural fibres (mineral and vegetal) in hybrid composites for designing sustainable composites for semi-structural applications; valorization of agro-industrial wastes as fillers in thermoplastic matrices (micro- and nanoscale); durability of composite materials based on thermoplastic and thermoset matrices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In the last two decades, the growing environmental issues have triggered the replacement of synthetic fibrous materials with lignocellulosic fibers characterized by biodegradability, easy availability, environmental friendliness, and good specific mechanical properties. Despite these benefits, their poor compatibility with polymer matrices still represents a major limitation for their industrial exploitation. In fact, their peculiar hydrophilic properties and surface characteristics prevent them from achieving a proper interfacial adhesion to hydrophobic polymer matrices, which leads to composites with poor mechanical properties. This Special Issue is aimed at collecting advancements made in the field of natural fibers and composites, including fiber–polymer interfacial strength. The aim is to increase our knowledge about the interfaces in natural fiber-reinforced polymer composites. Fundamental studies on fiber sizing or treatments at different scales (single fiber bundles or laminates) are particularly desirable. Both original research papers and reviews are welcome.

We hope that this Special Issue will provide the scientific community with relevant and innovative insights into fiber–matrix interfacial adhesion in natural fiber composites, with a view to broadening their application fields.

Dr. Pietro Russo
Prof. Fabrizio Sarasini
Guest Editors

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Keywords

Natural fibers
Fiber–matrix adhesion
Interface/Interphase phenomena
Sizing and surface modification
Natural fiber-reinforced polymers

Published Papers (7 papers)

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Research

19 pages, 5561 KiB

Open AccessArticle

Underutilized Agricultural Co-Product as a Sustainable Biofiller for Polyamide 6,6: Effect of Carbonization Temperature

by Thomas Balint, Boon Peng Chang, Amar K. Mohanty and Manjusri Misra

Molecules 2020, 25(6), 1455; https://doi.org/10.3390/molecules25061455 - 24 Mar 2020

Cited by 21 | Viewed by 4069

Abstract

Polyamide 6,6 (PA66)-based biocomposites with low-cost carbonaceous natural fibers (i.e., soy hulls, co-product from soybean industry) were prepared through twin-screw extrusion and injection molding. The soy hull natural fiber was pyrolyzed at two different temperatures (500 °C and 900 °C denoted as BioC500 and BioC900 respectively) to obtain different types of biocarbons. The BioC500 preserved a higher number of functional groups as compared to BioC900. Higher graphitic carbon content was observed on the BioC900 than BioC500 as evident in Raman spectroscopy. Both biocarbons interact with the PA66 backbone through hydrogen bonding in different ways. BioC900 has a greater interaction with N-H stretching, while BioC500 interacts strongly with the amide I (C=O stretching) linkage. The BioC500 interrupts the crystallite growth of PA66 due to strong bond connection while the BioC900 promotes heterogeneous crystallization. Dynamic mechanical analysis shows that both biocarbons result in an increasing storage modulus and glass transition temperature with increasing content in the BioC/PA66 biocomposites over PA66. Rheological analysis shows that the incorporation of BioC900 results in decreasing melt viscosity of PA66, while the incorporation of BioC500 results in increasing the melt viscosity of PA66 due to greater filler–matrix adhesion. This study shows that pyrolyzed soy hull natural fiber can be processed effectively with a high temperature (>270 °C) engineering plastic for biocomposites fabrication with no degradation issues. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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17 pages, 7723 KiB

Open AccessArticle

The Middle Lamella of Plant Fibers Used as Composite Reinforcement: Investigation by Atomic Force Microscopy

by Alessia Melelli, Olivier Arnould, Johnny Beaugrand and Alain Bourmaud

Molecules 2020, 25(3), 632; https://doi.org/10.3390/molecules25030632 - 1 Feb 2020

Cited by 42 | Viewed by 6950

Abstract

Today, plant fibers are considered as an important new renewable resource that can compete with some synthetic fibers, such as glass, in fiber-reinforced composites. In previous works, it was noted that the pectin-enriched middle lamella (ML) is a weak point in the fiber bundles for plant fiber-reinforced composites. ML is strongly bonded to the primary walls of the cells to form a complex layer called the compound middle lamella (CML). In a composite, cracks preferentially propagate along and through this layer when a mechanical loading is applied. In this work, middle lamellae of several plant fibers of different origin (flax, hemp, jute, kenaf, nettle, and date palm leaf sheath), among the most used for composite reinforcement, are investigated by atomic force microscopy (AFM). The peak-force quantitative nanomechanical property mapping (PF-QNM) mode is used in order to estimate the indentation modulus of this layer. AFM PF-QNM confirmed its potential and suitability to mechanically characterize and compare the stiffness of small areas at the micro and nanoscale level, such as plant cell walls and middle lamellae. Our results suggest that the mean indentation modulus of ML is in the range from 6 GPa (date palm leaf sheath) to 16 GPa (hemp), depending on the plant considered. Moreover, local cell-wall layer architectures were finely evidenced and described. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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16 pages, 12987 KiB

Open AccessArticle

Environmentally Friendly Surface Modification Treatment of Flax Fibers by Supercritical Carbon Dioxide

by Maria Carolina Seghini, Fabienne Touchard, Laurence Chocinski-Arnault, Vincent Placet, Camille François, Laurent Plasseraud, Maria Paola Bracciale, Jacopo Tirillò and Fabrizio Sarasini

Molecules 2020, 25(3), 438; https://doi.org/10.3390/molecules25030438 - 21 Jan 2020

Cited by 11 | Viewed by 3123

Abstract

The present work investigates the effects of an environmentally friendly treatment based on supercritical carbon dioxide (scCO₂) on the interfacial adhesion of flax fibers with thermoset matrices. In particular, the influence of this green treatment on the mechanical (by single yarn tensile test), thermal (by TGA), and chemical (by FT-IR) properties of commercially available flax yarns was preliminary addressed. Results showed that scCO₂ can significantly modify the biochemical composition of flax fibers, by selectively removing lignin and hemicellulose, without altering their thermal stability and, most importantly, their mechanical properties. Single yarn fragmentation test results highlighted an increased interfacial adhesion after scCO₂ treatment, especially for the vinylester matrix, in terms of reduced debonding and critical fragment length values compared to the untreated yarns by 18.9% and 15.1%, respectively. The treatment was less effective for epoxy matrix, for which debonding and critical fragment length values were reduced to a lesser extent, by 3.4% and 3.7%, respectively. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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15 pages, 2593 KiB

Open AccessArticle

Mechanical and Hydrothermal Aging Behaviour of Polyhydroxybutyrate-Co-Valerate (PHBV) Composites Reinforced by Natural Fibres

by Karolina Mazur and Stanisław Kuciel

Molecules 2019, 24(19), 3538; https://doi.org/10.3390/molecules24193538 - 30 Sep 2019

Cited by 34 | Viewed by 3012

Abstract

Biodegradable composites based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate), reinforced with 7.5% or 15% by weight of wood fibers (WF) or basalt fibers (BF) were fabricated by injection molding. BF reinforced composites showed improvement in all properties, whereas WF composites showed an increase in Young’s modulus values, but a drop in strength and impact properties. When compared with the unmodified polymer, composites with 15% by weight of BF showed an increase of 74% in Young’s modulus and 41% in impact strength. Furthermore, the experimentally measured values of Young’s modulus were compared with values obtained in various theoretical micromechanical models. The Haplin-Kardas model was found to be in near approximation to the experimental data. The morphological aspect of the biocomposites was studied using scanning electron microscopy to obtain the distribution and interfacial adhesion of the fibers. Additionally, biodegradation tests of the biocomposites were performed in saline solution at 40 °C by studying the weight loss and mechanical properties. It was observed that the presence of fibers affects the rate of water absorption and the highest rate was seen for composites with 15% by weight of WF. This is dependent on the nature of the fiber. After both the first and second weeks mechanical properties decreased slightly about 10%. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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12 pages, 3393 KiB

Open AccessArticle

Permeable Water-Resistant Heat Insulation Panel Based on Recycled Materials and Its Physical and Mechanical Properties

by Štěpán Hýsek, Miroslav Frydrych, Miroslav Herclík, Ludmila Fridrichová, Petr Louda, Roman Knížek, Su Le Van and Hiep Le Chi

Molecules 2019, 24(18), 3300; https://doi.org/10.3390/molecules24183300 - 11 Sep 2019

Cited by 9 | Viewed by 2824

Abstract

This paper deals with the development and characteristics of the properties of a permeable water-resistant heat insulation panel based on recycled materials. The insulation panel consists of a thermal insulation core of recycled soft polyurethane foam and winter wheat husk, a layer of geopolymer that gives the entire sandwich composite strength and fire resistance, and a nanofibrous membrane that permits water vapor permeability, but not water in liquid form. The observed properties are the thermal conductivity coefficient, volumetric heat capacity, fire resistance, resistance to long-term exposure of a water column, and the tensile strength perpendicular to the plane of the board. The results showed that while the addition of husk to the thermal insulation core does not significantly impair its thermal insulation properties, the tensile strength perpendicular to the plane of these boards was impaired by the addition of husk. The geopolymer layer increased the fire resistance of the panel for up to 13 min, and the implementation of the nanofibrous membrane resulted in a water flow of 154 cm² in the amount of 486 g of water per 24 h at a water column height of 0.8 m. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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14 pages, 1394 KiB

Open AccessArticle

Bio-Polyethylene-Based Composites Reinforced with Alkali and Palmitoyl Chloride-Treated Coffee Silverskin

by Franco Dominici, Daniel García García, Vicent Fombuena, Francesca Luzi, Debora Puglia, Luigi Torre and Rafael Balart

Molecules 2019, 24(17), 3113; https://doi.org/10.3390/molecules24173113 - 27 Aug 2019

Cited by 33 | Viewed by 3210

Abstract

This work investigates the feasibility of using coffee silverskin (CSS) as a reinforcing agent in biobased polyethylene (BioPE) composites, by adding it in bulk and thin film samples. The effect of two different treatments, alkali bleaching (CSS_A) and esterification with palmitoyl chloride (CSS_P), on mechanical, thermal, morphological and water absorption behavior of produced materials at different CSS loading (10, 20 and 30 wt %) was investigated. A reactive graft copolymerization of BioPE with maleic anhydride was considered in the case of alkali treated CSS. It was found that, when introduced in bulk samples, improvement in the elastic modulus and a reduction in strain at maximum stress were observed with the increase in CSS fraction for the untreated and treated CSS composites, while the low aspect ratio of the CSS particles and their poor adhesion with the polymeric matrix were responsible for reduced ductility in films, decreasing crystallinity values and reduction of elastic moduli. When CSS_A and CSS_P are introduced in the matrix, a substantial reduction in the water uptake is also obtained in films, mainly due to presence of maleated PE, that builds up some interactions to eliminate the amounts of OH groups and hydrophobized CSS, due to the weakened absorption capacity of the functionalized CSS. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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14 pages, 4653 KiB

Open AccessArticle

Effect of Fiber Surface Modification on the Interfacial Adhesion and Thermo-Mechanical Performance of Unidirectional Epoxy-Based Composites Reinforced with Bamboo Fibers

by Fang Wang, Min Lu, Shujue Zhou, Zhisong Lu and Siyan Ran

Molecules 2019, 24(15), 2682; https://doi.org/10.3390/molecules24152682 - 24 Jul 2019

Cited by 33 | Viewed by 3314

Abstract

In this work, bamboo fibers are chemically modified with NaOH solution of 1, 4, and 7 wt% concentrations at room temperature, respectively, and subsequently the untreated and treated fibers are prepared with epoxy resin for unidirectional composites by hot pressing molding technique. Tensile and micro-bond tests are conducted on the composite specimens to obtain mechanical properties, such as tensile strength and modulus, elongation at break, and interfacial strength. Besides, scanning electron microscopy (SEM) is employed to perform morphological observations for constituent damages. In addition, the influence of alkali concentration on the thermal performance of epoxy-based composites is examined by using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. It is found that composite tensile strength reaches the maximum when the alkali concentration is 4%, increased by 45.24% compared with untreated composites. The composite elongation at break increases on increasing the concentration. Inversely, the composite modulus decreases as the concentration increases. Besides, the results demonstrate that the chemical treatment on the fiber surface could improve interface adhesion, as observed from its topography by SEM. Micro-bond test reveals that there is maximum interfacial shear strength when the alkali concentration is 4%, which increases by 100.30% in comparison with the untreated samples. In case of thermal properties, the DSC analysis indicates that the glass transition temperature is maximized at 4% alkali concentration, which is increased by 12.95%, compared to those from unmodified fibers. In addition, TG results show that the 4% concentration also facilitates thermal stability improvement, indicative of superior interfacial bonding. Full article

(This article belongs to the Special Issue Advances in Natural Fiber Composites and Their Interfacial Adhesion)

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