Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

Javanshour, Farzin; Prapavesis, A.; Pärnänen, Tuomas; Orell, Olli; Belone, Maria Clara Lessa; Layek, Rama K.; Kanerva, Mikko; Kallio, Pasi; Vuure, Aart Willem Van; Sarlin, Essi

doi:10.1016/j.compositesa.2021.106628

Cited by 20 publications

(15 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The impact and fatigue tolerance of flax fibre composites are critical for their long-term durability [5][6][7][8]. The toughness of the reinforcing fibres and the polymer matrix [3,6,9], lay-up and architecture of the reinforcing fabrics [6], and interfacial toughness [10][11][12] are the critical parameters for composites' impact and fatigue tolerance. The primary failure mode of flax fibre composites is fibre failure with minor delamination, specifically in lowvelocity impact incidents, limiting the energy dissipation potential [6,10].…”

Section: Introductionmentioning

confidence: 99%

Impact and fatigue tolerant natural fibre reinforced thermoplastic composites by using non-dry fibres

Javanshour

Prapavesis

Pournoori

et al. 2022

Composites Part A: Applied Science and Manufacturing

Self Cite

View full text Add to dashboard Cite

Section: Introductionmentioning

confidence: 99%

Impact and fatigue tolerant natural fibre reinforced thermoplastic composites by using non-dry fibres

Javanshour

Prapavesis

Pournoori

et al. 2022

Composites Part A: Applied Science and Manufacturing

Self Cite

View full text Add to dashboard Cite

“…This is done because of a more moderate fibre swelling when the composite is exposed to the humid environment, since the fibres are already in a pre-swollen state due to the fabric preconditioning. Other treatments are primarily focusing on improving the fibre-matrix adhesion like silane, maleic-anhydride grafting [31], cellulose acetate [32], graphene-oxide [33], plasma treatment [34], etc. When this pretreatment step is used, the fibres will be less susceptible to water and thus the laminate will be less weakened.…”

Section: Moisture Diffusion and Absorptionmentioning

confidence: 99%

Hygroscopic cycling of flax fibre composites: Simultaneous swelling and shrinking of fibre and matrix

Timmermans¹

2022

Preprint

View full text Add to dashboard Cite

When natural fibres are exposed to humid environments, they absorb moisture and swell.Often, the natural fibre reinforced composites are produced in a combination with the widelyused non-/low-swelling matrices, like maleic anhydride grafted polypropylene (MAPP) andepoxy. The water uptake resulting in fibre swelling causes the build-up of internal stresseswhen the fibres are surrounded, and thus constrained, by the typically used matrices. Theseinternal stresses eventually lead to damage formation, resulting in loss of mechanicalproperties. The scope of this thesis is to investigate a potential strategy to decrease theaforementioned sensitivity of the natural fibre composites when exposed to hygroscopiccycling conditions. In this strategy the hydrophilic matrix polyamide-6 (PA6) will be used dueto its ability to absorb water and swell, resulting in a composite with decreased stress build-upby the hygroscopic expansion of the fibres, due to a matrix that swells and shrinks togetherwith the fibres.The hypothesis of having a good fibre-matrix interface when adding the hydrophilic matrix PA6to the hydrophilic flax fibres, was evaluated with a wettability analysis. A wettability analysisimplies using contact angle measurements to get an idea of the surface energy componentscalculated following the Van Oss model of both fibre and matrix. These surface energycomponents are then used to calculate the theoretical work of adhesion which shows thequality of the interface. Hygroscopic cycling is being applied on the traditional compositesflax/MAPP and flax/epoxy together with flax/PA6 composites to analyze their behavior after along durability cycling. The moisture content and sample thickness were monitored during theentire cycling process. After every cycle, a group of specimens was removed from the cyclingprotocol and mechanically tested in bending by using the three-point bending method.Therefore, mechanical degradation was monitored every cycle with a total of nine hygroscopiccycles performed. It is of great interest to take a closer look at the sample zone where failurehas occurred and investigate the failure mode. By using scanning electron microscopy (SEM),different damage mechanisms can be detected for the composites between the different testedcycles showing degradation of the materials.This study revealed that the hydrophilic matrix PA6 and flax fibres result in a high work ofadhesion value which shows a strong interfacial bonding and leads to a good impregnation ofthe thermoplastic. Furthermore, this was additionally supported by the high longitudinal andtransverse strength of the flax/PA6 composites as by the investigation of the fractured surfacesof the reference-unaged samples. The flax/PA6 samples obtain higher strength values thanthe flax/MAPP composites at the end of the long durability study. These observations aresupported by the analysis of the SEM pictures that indicate less damaged interfaces within theflax/PA6 specimens. In conclusion, the use of a hydrophilic matrix in natural fibre reinforcedcomposites shows promising results for composite materials exposed to humid environmentsfor a significant period

show abstract

“…Fiber treatments or fiber surface modifications are often applied to the reinforcing fibers to improve their compatibility with the matrix and thus improving the final properties of the composite [32,33].…”

Section: Fiber Treatmentsmentioning

confidence: 99%

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

Ivkov¹

2022

Preprint

View full text Add to dashboard Cite

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.

show abstract

Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

Cited by 20 publications

References 36 publications

Impact and fatigue tolerant natural fibre reinforced thermoplastic composites by using non-dry fibres

Impact and fatigue tolerant natural fibre reinforced thermoplastic composites by using non-dry fibres

Hygroscopic cycling of flax fibre composites: Simultaneous swelling and shrinking of fibre and matrix

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

Contact Info

Product

Resources

About