Moisture sorption and swelling of flax fibre and flax fibre composites

Lu, Maria Morissa; Fuentes, C.A.; Vuure, Aart Willem Van

doi:10.1016/j.compositesb.2021.109538

Cited by 57 publications

(33 citation statements)

References 35 publications

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“…As discussed earlier, the susceptibility of natural fiber-based composites to moisture/water has been well reported in the literature for different matrices [ 7 , 8 , 9 , 10 , 11 , 34 , 35 ]. Recently, Sanjeevi et al [ 35 ] have reported that for a hybrid phenol formaldehyde system with Areca fine fibers and Calotropis Gigantea fibers, the higher the natural fiber content in the composite, the higher was the water absorption rate.…”

Section: Resultsmentioning

confidence: 84%

“…However, it is important to acknowledge the drawbacks of using natural fibers in applications that are exposed to external weathering conditions or that demand high consistency in the performance. As well known, swelling of fibers is a major consequence of their susceptibility to moisture/water because of the presence of excessive hydroxyl groups (for example, see [ 7 , 8 , 9 , 10 , 11 ]). Despite many efforts in treating fibers (silane, acetylation, or even usage of maleic anhydride-based polymers) before incorporating them into different matrices (even non-polar matrices such as PP), the commercial success still awaits.…”

Section: Introductionmentioning

confidence: 99%

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Development and Characterization of Natural-Fiber-Based Composite Panels

Nair

Dasari

2022

Polymers

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The emphasis on sustainability in materials related to the construction and transportation sectors has renewed interest in the usage of natural fibers. In this manuscript, a different perspective is taken in adopting oil palm fibers (OPF) to develop composite panels and understand their acoustic, mechanical, and water susceptibility (including warm water analysis) properties to provide an insight into the potential of these panels for further exploration. The binder for these composite panels is a water-based acrylic resin, and for reinforcement purposes, fly ash and other metal oxides are used. It is shown that the presence of fibers positively influences the acoustic absorption coefficient in the critical mid-frequency range of 1000–3000 Hz. Even the noise reduction coefficient values highlighting the octave band are higher by more than 50% in the presence of fibers as compared to traditional refractory boards. Quasistatic indentation and drop-weight tests have also highlighted the excellent performance of the composite panels developed in this work. Though the water immersion tests on composite panels and subsequent analysis showed relatively minor changes in their performance, the immersion of the panels in caustic warm water for 56 days has resulted in their severe degradation with a loss of more than 65% in flexural strength.

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Section: Resultsmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Development and Characterization of Natural-Fiber-Based Composite Panels

Nair

Dasari

2022

Polymers

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“…The mass is measured with a digital scale with a precision of 4 digits and the thickness is measured with a digital micrometer. The formula below is used to calculate the moisture sorption [60]:…”

Section: Monitoring Of Sample Moisture Absorption and Swelling During...mentioning

confidence: 99%

A Study on Accelerated Ageing of Flax Fiber Reinforced Composites with Hygrothermal Cycling

Ivkov¹

2022

Preprint

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In terms of environmental impact, flax fiber reinforced composites are more sustainable and green than their contemporaries like carbon fiber and glass fiber reinforced composites while having similar mechanical properties. Rising crude oil prices and improvements in extraction and the use of natural fibers are making materials like flax fibers increasingly attractive for the composites industry. However, the main problem of flax fibers remains the fact that they are hydrophilic in nature. This makes them less suitable for high-humidity environments because of their tendency for moisture sorption, causing damage to the surrounding matrix when used in composites. The resulting internal swelling and shrinking accelerates the rate at which the material ages leading to a decrease mechanical properties. The goal of this thesis is to investigate accelerated ageing on flax fiber composite samples through means of hygroscopic cycling. Testing is carried out on a lab scale to simulate and predict how the mechanical properties of the material change throughout the course of its lifetime (up to 18 years of in-service behavior). This is done by expanding on previous research which suggests that an initial decline in strength and stiffness over the first few years curves back to an increase in the later years. In other words, the mechanical properties are observed to not decline continuously due to aging and start increasing after long exposure. This knowledge is used to lower the aforementioned primary drop in mechanical properties and rethink the possible fields of application for flax fiber reinforced composites. Practically, three main pillars are distinguished in this research, all of which involve the production and ageing of flax fiber composite samples: Accelerated lab-scale hygroscopic cycling of samples, natural ageing of samples and lastly precycling of flax fabrics before composite production. The precycling is carried out to induce fiber hornification, a phenomenon which aims to: improve compatibility with the matrix, improve the strength of the fibers and increase their hydrophobicity as options to slow down the ageing of the composites which they reinforce. The primary matrices that are used for this study are the thermoplastics maleic anhydride polypropylene (MAPP) and polyoxymethylene (POM; an engineering thermoplastic). Epoxy is used within the hygroscopic cycling and natural ageing because of its importance as an industrial standard. POM is six times stiffer than MAPP and boasts higher strength as well. The main problem of the POM matrix, however, is its inferior fiber-matrix adhesion compared to MAPP resulting in a weaker interphase. Flexural testing on the regularly cycled samples is still ongoing because of the long nature of the ageing of the samples. Testing on the shorter cycles suggests a significant decrease in strength of all materials, with properties dropping by 20%-40% after four hygroscopic cycles, similar to the damage caused by aging naturally. After eight cycles the strength increases by up to 30% for flax/MAPP and up to 23% for flax/POM when comparing to four cycles. This points to a clear prevalence of restrengthening over the course of the composites in-service lifetime. Thus, ageing of flax fiber composites paired with decreasing mechanical properties is not a continuous process. Flax/epoxy does not show significant drops in strength after eight cycles and retains at least 96% of its initial strength. For the precycled samples, continuously increasing mechanical strength is measured with increasing precycle time. For MAPP the strength increases with up to 12% in longitudinal fiber direction with the transverse fiber direction (the fiber-matrix interphase) increasing up to 6%. For POM, the increase is more profound: increases up to 15% in longitudinal fiber direction and up to 43% increase of interphase strength. With all data for precycling exhibiting these upward trends it can be said that the precycling of flax fiber fabrics before composite production can be employed as a tool to improve in-service properties and expand on the fields of application for flax fiber composites.

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“…Different components are responsible for the absorption of water in flax fibres: amorphous cellulose, hemicellulose and pectin [18]. This is mainly due to their amorphous structure and hydroxyl to carbon ratio [17].…”

Section: Moisture Absorptionmentioning

confidence: 99%

Effect of moisture absorption on the performance of flax fibre reinforced composites

Beelen¹

2022

Preprint

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The use of sustainable and environmentally friendly materials in today’s society is becoming increasingly important due to mankind’s increasing pressure on the carrying capacity of the planet. Natural fibre reinforced composites (biocomposites) can be used for this purpose as high-performance engineering materials. These biocomposites contain good specific properties and can therefore be used as an alternative to materials such as metals. Among natural fibres, flax has attracted high interest because it is among the highest performing natural fibres. However, these fibres have a hydrophilic character which makes them sensitive to humid environments. In this thesis, the extent to which water absorption takes place in these composites is investigated, as well as the impact this has on their mechanical properties.Several composites were produced for this research. There are three commercial types of flax fabrics that are combined with four matrices. These flax fabrics are FlaxTapeTM and two types of ampliTexTM. Then, there are the matrices, namely polypropylene, maleic anhydride polypropylene and polyoxymethylene, which are thermoplastic polymers. A final matrix that is used, is the thermosetting epoxy which is often used as reference due to the widespread use of as matrix for flax fibre reinforced composites. The selected fabrics are used to assess the impregnation quality due to their different structure. Therefore, optical microscopy images were taken of the various samples using a light microscope.To investigate the influence of humidity on the samples, they are first placed in environments with different moisture concentrations, varying from 23% to 97%. There, they remain until moisture saturation is achieved. One testing group of samples remained in the oven and are used as reference of a dry sample to investigate the properties directly after production and thus compare it with the composites after saturation in the various humidity levels.First, the diffusion speed of the moisture in the samples is analyzed. The samples are measured and weighed on a regular basis to determine the relative swelling and water absorption. Then the diffusion curves for the various composites are drawn up, whereby the diffusion coefficients are also calculated. In addition to the diffusion measurements, the maximum swelling and water absorption are measured for each moisture concentration at saturation. In the case of polypropylene and polyoxymethylene, diffusion takes place more rapidly than with the other matrices. The saturation values are close to each other for all composites with the same flax fabrics.After saturation, the samples were removed from the moist environments to measure the mechanical properties. Both longitudinal and transverse samples were analyzed. Based on these tests, flexural strength, flexural strain at failure and the flexural modulus were measured for the various composites. A decrease in properties can be observed with increasing moisture concentration. However, the decrease was shown to be depended on the type of fabric and matrix. Together with the microscopy images, it was noticed that the impregnation quality has a crucial role to reduce this drop on mechanical performance as function of humidity.Finally, after testing, the fractured surfaces were also studied using a scanning electron microscope. In this way, a larger influence of the compressive region was observed due to the appearance of buckling regions at high humidity levels.

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Moisture sorption and swelling of flax fibre and flax fibre composites

Cited by 57 publications

References 35 publications

Development and Characterization of Natural-Fiber-Based Composite Panels

Development and Characterization of Natural-Fiber-Based Composite Panels

A Study on Accelerated Ageing of Flax Fiber Reinforced Composites with Hygrothermal Cycling

Effect of moisture absorption on the performance of flax fibre reinforced composites

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