The present paper studies water absorption behavior and its consequence on mechanical properties of untreated and chemically treated Sansevieria /carbon fiber reinforced hybrid epoxy (Sria/CF-Ep) composite with calcium carbonate (CaCO 3) nanoparticles. Sansevieria /carbon fiber (30/5 wt%) reinforced hybrid epoxy composite with 1.5, 3 and 4.5 wt% of CaCO 3 have been developed by hand lay-up method followed by heat press. The water absorption characteristics of the Sria fibers were obtained by immersing the composite samples in sea water at room temperature, until reaching their water content saturation level. The dry and water-immersed hybrid composite samples were subjected to hardness, interlaminar shear, tensile, flexural, and impact tests. The water absorption development of hybrid composites was found to follow Fickian diffusion behavior. Diffusion coefficients and maximum water uptake results were evaluated; the outcome showed that both increased with an increase in filler loading to study the consequence of water penetration in the fiber/matrix interface. The study shows that the mechanical and water-resistant properties of the Sria were improved through chemical treatment and hybridization. Nevertheless, as a result of water penetrating the fiber/matrix interface, longer water-immersion times reduced the tensile and flexural strength of the composites.
The environmental awareness in addition to the government stringent rules throughout the globe has encouraged the scholarly and industrial researches to expand eco-friendly, sustainable, and biodegradable composite materials, as a result often referred to as green composites [
Areas such as automotive and construction [
Plant fiber reinforced composites are hydrophilic and hygroscopic materials. Moisture content in plant fiber composites considerably affects their physical and mechanical properties. Moisture transfer in plant and plant fiber composites influences dimensional steadiness, viscoelastic properties, fiber play a vital role in the ageing of bio-composites in a wet atmosphere or by immersion in water and durability. These parameters lead to a lowered fiber/matrix bonding strength those results in a weaker mechanical performance of fiber/matrix hybrid composites [
Less than the fiber saturation point, moisture transport by the plant fiber is restricted by diffusion. Bounce moisture diffusion is a grouping of two movements: the vapor diffusion by void structure, and the bound water diffusion by the cell wall. A diffusion model based on Fick’s second law has been created to describe corresponding mass transfer process. The transfer of water molecules by the micro cracks that can appear in the matrix as a result of the fiber swelling. According to this mechanism, there are three cases of diffusion behaviour [
Moisture absorption is a big hurdle in the growth to utilize natural fibers in composites because the mechanical properties of composites degrade and reduce in wet conditions. The opportunity for using these fresh materials in outdoor applications requires complete study and to evaluate their mechanical characteristic in a violent environment, mainly in a moisture environment, during a long time. In addition synthetic fibers like glass (GF) or carbon fibers (CF), short aramid fibers (AF) are adopted to intensify the compressive strength and the creep resistance of the polymer matrix composites [
Toughness is the ability of a material to sustain its original mechanical, thermal, physical and chemical properties for several years. For oceanic application, composites are estimated to be robust and not to be degraded in seawater for extended age of time. Owing to the viscoelastic behavior of polymeric matrix, composites exhibit time-dependant degradation in modulus and strength [
Selection of resin is also very important parameter for designing a FRP for marine applications so epoxy resin is considered because it represents several of the highest performance resin due to the mechanical properties and resistance to environmental degradation, which leads to their almost exclusive use in aircraft components, marine application etc. Epoxies are distinct as cross-linked polymers which have cross-linking derived from chain reactions of the epoxy group. Epoxy resin typically used in coating industry as surface coating materials that combine flexibility, toughness, adhesion, and chemical resistance [
Glass/polyurethane and glass/epoxy are amongst various materials suggested for use in marine infrastructure. Many researchers have investigated the consequences of moisture on glass/epoxy composites [
Carbon/epoxy composites are appropriate for light weight structures and may be a healthier substitute to other materials presently in use in oceanic applications. Although there have been a number of work on the mechanical behavior of carbon/epoxy composites, to the best of our understanding, no studies have been reported in the literature on the effects of sea water on mechanical properties of nano-sized CaCO3 filled Sria/carbon fiber epoxy composites. The objective of this study is to investigate the effects of sea water on the mechanical properties of CaCO3 filled Sria/CF-Ep composites.
In the present investigation unidirectional sansevieria (Sria) plant fiber which was collected from farm near Annur, Tamil Nadu, India, using a mechanical procedure called decortication. The extracted plant fibers are weaved in mat form such that all fibers are oriented unidirectional. Unidirectional carbon fibers (CFs) woven was collected from Master Micron International, Bengaluru, India. Nanofillers like calcium carbonate (CaCO3) were obtained from Global nanotech, Kolkata, India. Epoxy (Lapox-12, K6 hardener) resin was purchased from Yuje Enterprises, Bengaluru, India.
The sansevieria (Sria) fibers were drenched in a glass tray containing 4.5% NaOH solution for 1 h. After that the fibers were washed carefully with distilled water in order to get rid of the excess NaOH content in the fibers [
The composite materials used for the existing investigation is fabricated by way of hand layup process. Sria fiber unidirectional woven mat of 300 mm × 300 mm size and unidirectional woven carbon fibers were used to put together the final slabs. The chemically handled Sria fiber mats were stored beneath daylight for 6 h and in addition dried in hot air oven for 2 h to get rid of the dampness content in the fibers. The composite slab consists of whole three layers in which carbon fibers layers are positioned at the top and backside of Sria mat. The layers of fibers are fabricated through smearing the required quantity of epoxy and hardener mix over the stacked mats and two rollers are used to trick all the air bubbles. During fabrication, the fiber orientation and alignment in the composites is maintained via two metal rollers that are always rolled on the fiber in the die. The procedure is repeated for preparation of nano-hybrid composites by way of mixing CaCO3 nanofiller with epoxy with special wt.%. Finally these stacked composite slabs are taken to the hydraulic press for curing and the period of cure is maintained for about 24 h (final size after cure: 300 × 300 × 4.5 mm3).
Designation | Composition (wt.%) | CaCO3 (wt.%) |
---|---|---|
S1 | Sria (30%) + Ep (70%) | 0 |
S2 | Sria (30%) + CF (5%) + Ep (65%) | 0 |
S3 | Sria (30%) + CF (5%) + Ep (63.5%) | 1.5 |
S4 | Sria (30%) + CF (5%) + Ep (62%) | 3 |
S5 | Sria (30%)+ CF (5%) + Ep (60.5%) | 4.5 |
Sria―Sansevieria Fiber, CF―Carbon Fiber, Ep―Epoxy.
Water absorption tests were conducted as per ASTM D570 [
Δ M ( t ) = M t − M o M o × 100 (1)
MO and Mt symbolize the mass of the dry and immersed sample, at exact time. The moisture absorption percentage was plotted against the square root of time (hours). The effects of ageing on the hardness, Interlaminar shear strength, tensile, and flexural properties of the woven composites were investigated after 792 h (at saturation).
Several linear Fickian diffusion processes for composites were listed [
D = π ( h 4 M ∞ ) 2 ( M 2 − M 1 t 2 − t 1 ) 2 (2)
where, M∞ is the percent moisture absorbed at saturation, h is the specimen thickness; M 2 − M 1 is the slope of the plot of the moisture absorption rate during the first ageing time and t 2 − t 1 is the linear portion of the curve. Assuming the absorption process is linear at an early stage of immersion; times are taken at the beginning of absorption process, so that the weight change is expected to vary linearly with the square root of time.
The hardness of Sria/Ep (S1) primarily based hybrid nanocomposites was decided in accordance to ASTM D2583 standard [
The Interlaminar shear strength (ILSS) of the Sria/Ep primarily based hybrid nanocomposites was measured using a Universal Testing Machine (Kalpak Instruments & Control, K TEST Series, 100 kN), based on the ASTM D2344 [
The tensile tests for Sria/Ep primarily based nanocomposites had been carried out using Universal Testing Machine (Kalpak Instruments & Control, K TEST Series, 100 kN) at a cross head speed of 5 mm/min, using 4 coupons for every measurement. An extensometer with gauge length 50 mm was once used for the elongation measurements, at room temperature as per ASTM D-638 [
Izod impact test has been performed under ASTMD256 standard [
Fracture surfaces obtained from tensile assessments have been examined via Scanning Electron Microscopy (SEM) using JSM-7900F equipment. Prior to SEM observation, all tensile broken coupons were sputter coated with a skinny layer of gold to keep away from electric charging.
Water absorption of Sria/CF-Ep composites with varying percentage of CaCO3 are shown in
increase in water absorption and after a certain time all composites start to reduce the water uptakes from the surrounding till it reach saturation point. Saturation point is where composite absorb no more water and the water content in composite remained constant. Related work was highlighted in earlier works where the water absorption effects of natural fiber reinforced polymer composites were investigated [
On the other hand, while the composites are constantly exposed to water, the brittle thermosetting resin will experience micro cracking due to the swelling behaviour of the fibers. Cellulose content in the Sria fibers additional supports to more water penetrating into the fiber-matrix interphase developing stress concentration leading to failure of the composite. While, more micro cracks were found in coupons and water transport through these micro cracks [
Furthermore, the addition of nanofiller CaCO3 in composites had increased the moisture absorption rate. This might be due to the properties of the CaCO3 that have high tendency to agglomerate. It is well recognized that the smaller the
size of particle the more easily the particle to agglomerate. This agglomeration would have damaged the interfacial adhesion between the filler and matrix which therefore lead to variation in the formation of gap in interfacial region. Raising the gap in interfacial region could increase the amount of water molecules to penetrate into composite and the being trapped inside the gap.
From literature, it is understood that filler had superior tendency to produce agglomerate. Results showed that the water absorption of Sria/CF-Ep composite was increasing with addition of CaCO3 filler loading. This could be due to the higher cellulose in Sria fiber, When CaCO3 introduced in the composite; the presence of high amount of agglomeration had increased the gap in interfacial between the filler and matrix therefore increasing the water absorption of the composite. Nevertheless, the amount of cellulose in Sria fiber given more impact for water absorption properties compared to the gap appears between the filler and matrix in all filled composites. Sria fiber had the ability to absorb water due to the high cellulose content which formed high hydrogen bonding from its hydroxyl group and water molecules.
Even though CaCO3 have hydrophilic sites and polar, it may not be as fine as the cellulosic fibers of the Sria do attract water content. Also, the Sria fiber used in this study was potassium permanganate treated. Therefore, the possibility to absorb water molecule are minimal, predictable to be brought about by Sria fiber compare to CaCO3 filler loading in the hybrid composite.
dry samples. This could additionally be credited to degree of cure of the epoxy resin, consistent dispersion and higher interfacial bonding between the CaCO3 particles in the epoxy resin. In the same way, the hardness improved for composites containing CaCO3 and their hybrid sample composites.
The interlaminar shear strength (ILSS) consequences of CaCO3 crammed S2 hybrid composites are proven in
This enhancement in ILSS can be credited to the uniform dispersion of CaCO3 inside the epoxy matrix, which helps in growing the bonding between the fibers and higher transfer of stress. Correspondingly the water absorbed samples ILSS decreased when compared to the same dry samples this may be attributed to the water absorption behaviour of Sria fiber and CaCO3.
The results of the tensile properties obtained for S1, S2, and their composites are shown in
with minimum compression. Increased fiber outside region provides the ductile polymer with more capability in order to capture and transfer stress to the fiber. Further, the composite strength is considerably influenced by the orientation of reinforcing fibers within the epoxy matrix.
For S2 composite filled with different wt.% of nano CaCO3, the tensile strength increased from 145 MPa to 240 MPa. The tensile moduli of 1.5, 3.0 and 4.5 wt.% nano CaCO3 filled hybrid composites are 39%, 61% and 67% higher than that of S2 (1.41 GPa), respectively (
The flexural properties of S2 and their nanofillers stuffed hybrid composite are illustrated in
the minimal flexural strength was 263.22 MPa in the control group without CaCO3 (S2).
The flexural strength improved as the CaCO3 quantity in the hybrid nanocomposite system increased. This was attributed to the top compatibility between the CaCO3, carbon/chemically treated Sria fibers, and epoxy matrix. The outcomes confirmed similarities to research in the literature [
The outcomes of the impact strength testing of S1, S2, and their nano-CaCO3 stuffed hybrid composites (S3 to S5) is proven in
The most increase of 67% has been confirmed with the aid of 4.5 wt.% CaCO3 crammed S2 hybrid composites. Fibers and fillers play a vital role in enhancing the impact resistance of the material, which is related to the usual longevity of the material. With the increase of nanofiller loading, the interfacial adhesion between fiber, epoxy resin, and nanofiller increase, which assist in higher load transfer and promotes stress switch from fiber and filler to the matrix. Furthermore, the cause for this behaviour was the large amount of nanoparticles of the CaCO3/Sria/CF phase and their appropriate dispersion in the epoxy matrix inflicting an extended transfer of impact energy to the fiber and filler phase. This
implies that stronger interfacial interplay between chemically dealt Sria fiber/ carbon fiber phase and CaCO3 phase improved the impact strength of the epoxy.
The mechanical properties of fabricated Sria/Ep, Sria/CF-Ep and their nano-CaCO3 stuffed hybrid composites are evaluated. The following conclusions have been derived from the experimental investigations.
・ Sansevieria fibers can be efficaciously modified by way of bodily and chemical treatments. Potassium permanganate treated sansevieria fibers brings about an active surface by means of introducing some reactive groups and grant the fibers with larger extensibility via partial elimination of lignin and hemicellulose.
・ The profitable fabrication of Sria/EP and Sria/CF-Ep composites with different share (0 to 4.5 wt %) of nano-CaCO3 filler loading can be accomplished via easy by simple hand lay up procedure accompanied by heat press.
・ The hardness and interlaminar shear strength test outcomes confirmed that the Sria/CF-Ep composite with nano-CaCO3 improved properties when compared to water absorbed Sria/Ep and Sria/CF-Ep hybrid composites. The dry composite Sria/CF-Ep with 4.5 wt.% nano-CaCO3 (S5) sequence presented the best interlaminar shear strength.
・ The tensile and flexural properties of mono-composite (Sria/-Ep, S1) multiplied with small weight share of carbon fibers (5 wt.%) and an increased quantity of nano-CaCO3 filler. The greater values may perhaps due to the fact of good dispersion of nano-CaCO3 particles in the epoxy matrix material. Also showed the decreasing trend with the water absorption for the same samples.
・ The notched Izod have an effect on tests confirmed an increase in the impact energy of both Sria/CF and CF with varied CaCO3 coupons (S2 to S5) as in contrast to the mono-composite (Sria/Ep, S1). The highest impact strength of 643 J/m used to be bought for 4.5 wt.% CaCO3 nanoparticles stuffed Sria/ CF-Ep as compared to mono-composites. These outcomes suggest that the used nano-modifier in the hybrid fiber bolstered epoxy matrix introduced a proper compatibility with each carbon/chemically treated Sria fiber, with the benefit of increasing the mechanical properties of the epoxy matrix material.
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no financial support for this work that could have prejudiced its outcome.
Anjum, N., Suresha, B. and Prasad, S.L.A. (2019) Influence of Water Ageing on Mechanical Properties of CaCO3 Filler Filled Epoxy Resin and Sansevieria/Carbon Fiber Reinforced Com- posites. Open Journal of Composite Materials, 9, 1-20. https://doi.org/10.4236/ojcm.2019.91001