Exploring Mechanical Adhesion in Fiber Reinforced Composites with Aramid and Recycled Carbon Fibers

Polymeerikomposiitit ovat monipuolinen materiaali ryhmä, joille tyypillisiä ominaisuuksia ovat muun muassa suuri lujuus ja jäykkyys yhdistettynä keveyteen. Kuitenkin vain oikeilla materiaalivalinnoilla, rakenteen optimoinnilla ja oikeanlaisella valmistusmenetelmällä voidaan aikaansaada kestävä ja toimiva komposiittirakenne, joka täyttää halutut vaatimukset. Komposiitit koostuvat matriisista ja lujitteesta, jotka yhdessä muodostavat kevyen ja kestävän kokonaisuuden. Kuitenkin, mikäli matriisin ja lujitteen välille ei onnistuta muodostamaan kestävää rajapintaa, koko rakenteen kuormankantokyky on puutteellinen. Pahimmassa tapauksessa huono rajapinnan adheesio voi johtaa koko komposiittikappaleen ennakoimattomaan murtumiseen ja rikkoutumiseen. Tämän väitöskirjan tavoitteena on määrittää miten mekaanisen adheesion kasvattaminen kuitu-matriisirajapinnalla vaikuttaa kyseisen rajapinnan kokonaisadheesio-ominaisuuksiin polymeerikomposiitissa. Lisäksi tavoitteena on selvittää, voidaanko tämä vaikutus nähdä eri kokoisissa komposiittirakenteissa sekä erilaisilla materiaaliyhdistelmillä. Tavoitteiden toteuttamiseksi kaksi lähestymistapaa valittiin: aramidikuitujen pinnanmuokkaus kehittämällä uusi pintakäsittelymenetelmä sekä valmiiksi teksturoitujen kierrätettyjen hiilikuitujen hyödyntäminen. Näistä kuiduista valmistettiin mikro- ja makroskaalan komposiitteja, joiden kuitu-matriisirajapinnan lujuus mitattiin. Lisäksi pintakäsittelymenetelmän vaikutusta kuitujen ominaisuuksiin tutkittiin vetokokeilla, elektronimikroskoopilla sekä atomivoimamikroskoopilla. Tulokset osoittivat, että mekaanisen adheesion lisääminen rajapinnalla lisää myös rajapinnan lujuutta kokonaisuudessaan. Jopa nanokokoiset partikkelit, jotka ovat tiukasti kuidun pinnassa kiinni, lisäävät kuitu-matriisirajapinnan adheesiota, vaikuttamatta kuitenkaan kuidun mekaanisiin omaisuuksiin negatiivisesti. Lisäksi havaittiin, että lisääntynyt rajapinnan lujuus näkyy sekä kerta- ja kestomuovi- sekä kumimatriisissa että eri kokoskaalan komposiiteissa. Tällä tavoin aramidi- ja hiilikuitujen käyttöpotentiaalia voidaan laajentaa ja näin mahdollistaa siirtymä kohti ekologisesti kestävämpää komposiittien valmistusta näiden kahden erikoislujan kuidun kohdalla.Polymer composites are a versatile group of advanced materials with high strength, low weight and high stiffness. To achieve these properties special care must be taken in the manufacturing process of each composite structure starting from material selection to compounding and assembly. Composites are composed of matrix material and reinforcing material. The combination of these two elements is what gives the composite its unique properties. However, if these elements are not joined together properly through interfacial adhesion the load carrying capacity of the structure is compromised. In the worst case, poor adhesion may cause catastrophic failure of the whole composite. The objective of this thesis is to identify what effect does increased mechanical adhesion at the fiber-matrix interphase in fiber reinforced polymer composites have on the adhesion properties. In addition, the goal is to determine if this effect can be observed in composite structures of different size scales and material combinations. To achieve these goals, two case studies were investigated: development of a novel surface treatment method for aramid fibers to create increased surface topography and utilization of recycled carbon fibers with pronounced surface topography acquired through an adjoining project. Using these two fiber types, micro and macroscale composites were manufactured and the adhesion between fibers and matrix measured. In addition, the effect of the surface treatment on the fibers was tested with single filament tensile tests, electron microscopy and atomic force microscopy. The results of this study showed that by increasing mechanical adhesion at the fiber-matrix interphase the overall interfacial adhesion is increased also. Even nanoscale structures that are firmly attached to the fiber surface, have a positive effect on the adhesive properties without affecting the fiber properties negatively. In addition, it was shown that the increased adhesion can be observed in thermoset, thermoplastic and rubber matrices in different size scales. This broadens the use- potential of aramid and recycled carbon fibers and enables a transition towards more sustainable composite manufacturing with these two advanced fiber materials

Towards Sustainable Composite Manufacturing with Recycled Carbon Fiber Reinforced Thermoplastic Composites

Currently, the vast majority of composite waste is either landfilled or incinerated, causing a massive burden on the environment and resulting in the loss of potentially valuable raw material. Here, conventional pyrolysis and reactive pyrolysis were used to reclaim carbon fibers from aeronautical scrap material, and to evaluate the feasibility of using reclaimed carbon fibers in structural components for the automotive sector. The need for fiber sizing was investigated as well as the behavior of the fiber material in macroscopic impact testing. The fibers were characterized with the single fiber tensile test, scanning electron microscopy, and the microbond test. Critical fiber length was estimated in both polypropylene and polyamide matrices. Tensile strength of the fiber material was better preserved with the reactive pyrolysis compared to the conventional pyrolysis, but in both cases the interfacial shear strength was retained or even improved. The impact testing revealed that the components made of these fibers fulfilled all required deformation limits set for the components with virgin fibers. These results indicate that recycled carbon fibers can be a viable option even in structural components, resulting in lower production costs and greener compositesThis research was partly funded by FINNISH CULTURAL FOUNDATION, grant number 00210821, and EU H2020-IND-CE project “FiberEUse” (grant agreement number 730323)

Weathering of Antibacterial Melt-Spun Polyfilaments Modified by Pine Rosin

For many antibacterial polymer fibres, especially for those with natural functional additives, the antibacterial response might not last over time. Moreover, the mechanical performance of polymeric fibres degrades significantly during the intended operation, such as usage in textile and industrial filter applications. The degradation process and overall ageing can lead to emitted volatile organic compounds (VOCs). This work focused on the usage of pine rosin as natural antibacterial chemical and analysed the weathering of melt-spun polyethylene (PE) and poly lactic acid (PLA) polyfilaments. A selected copolymer surfactant, as an additional chemical, was studied to better integrate rosin with the molecular structure of the plastics. The results reveal that a high 20 w-% of rosin content can be obtained by surfactant addition in non-oriented PE and PLA melt-spun polyfilaments. According to the VOC analysis, interestingly, the total emissions from the melt-spun PE and PLA fibres were lower for rosin-modified (10 w-%) fibres and when analysed below 60 ℃. The PE fibres of the polyfilaments were found to be clearly more durable in terms of the entire weathering study, i.e., five weeks of ultraviolet radiation, thermal ageing and standard washing. The antibacterial response against Gram-positive Staphylococcus aureus by the rosin-containing fibres was determined to be at the same level (decrease of 3–5 logs cfu/mL) as when using 1.0 w-% of commercial silver-containing antimicrobial. For the PE polyfilaments with rosin (10 w-%), full killing response (decrease of 3–5 logs cfu/mL) remained after four weeks of accelerated ageing at 60 ℃

Perspectives on the industrial implementation of novel microwave assisted surface modification method for aramid fibers

Aramid fibers are synthetic aromatic polyamide fibers that are currently used in demanding composite applications, such as tires, hoses, bulletproof vests and helmets. They are manufactured by solution spinning from sulphuric acid solution. Due to the manufacturing method and the chemical nature of aramid, the fiber surface is very smooth and inert, which affects the adhesion properties of the fibers negatively. Several surface treatment methods are used to increase the adhesion between the fibers and matrix materials in composite products. Some of these methods have major drawbacks, creating pressure to develop new surface treatment methods for the industry. In this article a surface treatment method that uses microwave irradiation combined with reactive chemicals is used to increase the adhesion between the aramid fibers and a rubber matrix. The method increased the adhesion by a factor of~ 3.5 when

Perspectives on the industrial implementation of novel microwave assisted surface modification method for aramid fibers

Aramid fibers are synthetic aromatic polyamide fibers that are currently used in demanding composite applications, such as tires, hoses, bulletproof vests and helmets. They are manufactured by solution spinning from sulphuric acid solution. Due to the manufacturing method and the chemical nature of aramid, the fiber surface is very smooth and inert, which affects the adhesion properties of the fibers negatively. Several surface treatment methods are used to increase the adhesion between the fibers and matrix materials in composite products. Some of these methods have major drawbacks, creating pressure to develop new surface treatment methods for the industry. In this article a surface treatment method that uses microwave irradiation combined with reactive chemicals is used to increase the adhesion between the aramid fibers and a rubber matrix. The method increased the adhesion by a factor of~ 3.5 when

Development in additive methods in aramid fiber surface modification to increase fiber-matrix adhesion: A review

This review article highlights and summarizes the recent developments in the field of surface modification methods for aramid fibers. Special focus is on methods that create a multifunctional fiber surface by incorporating nanostructures and enabling mechanical interlocking. To give a complete picture of adhesion promotion with aramids, the specific questions related to the challenges in aramid-matrix bonding are also shortly presented. The main discussion of the surface modification approaches is divided into sections according to how material is added to the fiber surface; (1) coating, (2) grafting and (3) growing. To provide a comprehensive view of the most recent developments in the field, other methods with similar outcomes, are also shortly reviewed. To conclude, future trends and insights are discussed

One surface treatment, multiple possibilities : Broadening the use‐potential of para‐aramid fibers with mechanical adhesion

Aramid fibers are high‐strength and high‐modulus technical fibers used in protective clothing, such as bulletproof vests and helmets, as well as in industrial applications, such as tires and brake pads. However, their full potential is not currently utilized due to adhesion problems to matrix materials. In this paper, we study how the introduction of mechanical adhesion between aramid fibers and matrix material the affects adhesion properties of the fiber in both thermoplastic and thermoset matrix. A microwave‐induced surface modification method is used to create nanostructures to the fiber surface and a high throughput microbond method is used to determine changes in interfacial shear strength with an epoxy (EP) and a polypropylene (PP) matrix. Additionally, Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy were used to evaluate the surface morphology of the fibers and differences in failure mechanism at the fiber‐matrix interface. We were able to increase interfacial shear strength (IFSS) by 82 and 358%, in EP and PP matrix, respectively, due to increased surface roughness and mechanical adhesion. Also, aging studies were conducted to confirm that no changes in the adhesion properties would occur over time.publishedVersionPeer reviewe