Seawater Aging Research Articles

Feasibility of Recovering and Recycling Polymer Composites from End-of-Life Marine Renewable Energy Structures: A Review

Over the last few decades, several marine renewable energy (MRE) technologies, such as wave energy converters (WECs) and current energy converters (CECs), have been developed. As opposed to traditional materials such as metal alloys, the structure of these technologies is made up of polymer and polymer composite materials. Most structures have been made using thermoset polymer composites; however, since thermoset polymer composites are not recyclable and lack sustainability, and with recent innovations in recyclable resins, bio-based resins, and the development of additive manufacturing technologies, thermoplastic polymers are increasingly being used. Nevertheless, the methodologies for identifying end-of-life options and recovering these polymer composites, as well as the recycling and reuse processes for MRE structures, are not well-studied. Specifically, since these MRE structures are subjected to salinity, moisture, varying temperature, biofouling, and corrosion effects depending on their usage, the recyclability after seawater aging and degradation needs to be explored. Hence, this review provides an in-depth review of polymer composites used in marine applications, the hygrothermal aging studies conducted so far to understand the degradation of these materials, and the reuse and recycling methodologies for end-of-life MRE structures, with a particular emphasis on sustainability.

Investigation of the hygrothermal effects on in-plane failure mechanisms of fine Z-pinned laminates

Hygrothermal effect on the in-plane behavior of fine Z-pinned laminates were studied and the failure mechanisms were explained. Artificial seawater aging experiments were carried out on Z-pinned laminates prepared by ultrasonic vibration equipment. A compression progressive damage numerical model of fine Z-pinned laminates based on moisture-induced interface degradation was proposed to analyze the damage initialization and development of composites. The mechanical results show that the unpinned and Φ0.11 mm Z-pinned laminates have similar in-plane strength retention after 6 months of aging, and the tensile and compressive strengths decrease by 20% and 29%, respectively. EDS analysis confirms that Z-pin provides an additional moisture channel, leading to more elements with high relative atomic mass inside the laminates. It is found through the simulation studies that moisture leads to matrix compression and interlaminar interfacial damage regions to localized areas, weakening the interlayer effect of Z-pins and leading to the decrease of the ultimate bearing capacity of laminates. It denotes that Φ0.11 mm fine Z-pin has the potential to be used in composite marine structures.

Marine durability of carbon black-filled polychloroprene: Effect of seawater ageing on network, tensile and fatigue properties

With the development of marine renewable energies, the durability of materials at sea is more than ever a major issue in reducing the risk of failure of offshore devices. In this aggressive environment, elastomers, and in particular polychloroprene (CR), have many applications because of their good damping and fatigue properties. However, these materials are subject to ageing in service, which leads to changes in their mechanical properties. The ageing of these materials in a marine environment has not been extensively studied, despite the need to predict components lifetimes. This paper investigates the mechanical and microstructural consequences of a carbon black-filled CR degradation when exposed to seawater. To this end, swelling, uniaxial tensile and fatigue tests are carried out on materials previously subjected to accelerated ageing in natural seawater. Particular attention is paid to understanding the physico-chemical phenomena involved, and analysing fracture and fatigue properties in relation to those of the macromolecular network.

Degradation of Prestressed GFRP Bars Embedded in Seawater–Sea Sand Geopolymer Mortars under Hydrothermal Seawater Aging

Degradation of Prestressed GFRP Bars Embedded in Seawater–Sea Sand Geopolymer Mortars under Hydrothermal Seawater Aging

Adsorption-desorption behavior of malachite green on aged microplastics in seawater environment

The role of microplastics (MPs) as carriers of contaminants in the water environment is an emerging concern, significantly impacting migration and transformation. This study aims to compare the adsorption behavior of MPs with Malachite green (MG) dye before and after simulated short-term seawater aging (especially during the initial phase of the aging process) and to analyze in-depth the mechanism by which the aging process influences adsorption behavior. Results showed that after aging, the adsorption capacities of Polypropylene (PP), Polyethylene terephthalate (PET), and Polyethylene (PE) for MG were 2.58, 2.43, and 1.59 mg g−1, respectively. The adsorption capacity of other MPs for MG increased significantly, except for PE, which remained nearly unchanged. Calcium chloride (CaCl2) plays a significant role in the seawater aging process, and increasing the concentration of CaCl2 leads to a decrease in the adsorption amount of MG. Additionally, the adsorption capacity for MG varies significantly across different particle sizes and types of MPs, as well as the adsorption capacity of PP for different dyes. The Langmuir and Freundlich models indicate that the adsorption aligns more with the Freundlich model, which suggests that adsorption primarily occurs as multi-layer adsorption on a non-homogeneous surface. These results provide a scientific foundation for evaluating the ecological and environmental risks when MPs and organic dyes coexist. We also propose a novel approach of “treating waste dye with MPs” to mitigate their pollution in the aquatic environment.

Effect of various aging conditions and treatment methods on thermal degradation of coffee waste/epoxy composites

In composites containing lignocellulosic fillers, the chemical composition of the filler mostly determines the heat resistance. Based on the rules of green chemistry, new bio-based composites were developed from the waste of industrial crop product coffee (CW), and their thermal stability in different aging environments was examined by thermogravimetric analysis (TGA). Alkali (NaOH), microwave (MW), ultrasound (US), and alkali pretreatment followed by microwave (NaOH+MW) were applied to modify the CW. The effect of various applied treatment methods and environmental conditions such as UV radiation, water sorption, seawater, and hydrothermally agings on the thermal properties of the composites was investigated. Fourier-transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FE-SEM) were used in the characterization of composites. Among the environmental factors tested, seawater and hydrothermal aging affected the thermal resistance of the composites the most, while NaOH+MW affected it most among the processing methods. Although the thermal stability of unaged and UV-exposed MW-CW composites was found to be the highest, it was more affected by aging in seawater, pure water, and hydrothermal environments. As a result, MW was found to be more effective among the treatment methods in terms of thermal properties under UV conditions, confirming that the adoption of environmentally friendly methods and surface modification of the filler can provide superior composites.

Mechanical and biodegradation analysis under various environmental conditions of the waste vetiver root fiber reinforced soy composite

AbstractTo address the difficulty posed by non‐biodegradable thermoplastics, scientists are focusing on solid waste management research. Waste vetiver root fibers reinforced in polymerized soy matrix biomass composites were fabricated and tested for biodegradability and sustainability in different natural decomposing conditions like seawater aging and fungal and termite attacks. This study reports and compares the dimensional changes caused by these attacks, as well as the moisture absorption of vetiver‐soy and alkali‐treated vetiver‐soy composites at different relative humidity. After‐degradation characterizations included Fourier transform infrared spectroscopy and SEM examinations, as well as weight loss, which gave additional insights into the degradation mechanism. The tensile strength of degraded samples decreased as the degradation duration increased. Mechanical properties like Izod impact strength, dynamic mechanical analysis and moisture absorption also provided insights into the structural firmness of the fabricated composite. This research contributes to a better knowledge of the bio‐deterioration process of cellulosic vetiver‐soy biocomposites under various situations, and to check their functionality in furniture and packaging industries. © 2024 Society of Chemical Industry.

Accelerated seawater ageing and fatigue performance of glass fibre reinforced thermoplastic composites for marine and tidal energy applications

The use of thermoplastic composites as a sustainable alternative to thermosets is gaining increasing popularity due to their improved recyclability at the end of life. The fatigue performance of glass fibre/acrylic, glass fibre/acrylic- polyphenylene ether, and glass fibre/epoxy specimens, under three distinct upper stress levels (R-ratio = 0.1; f = 5 Hz) was studied. S–N curves were established for these specimens both before and after immersing them for three months in seawater (temperature: 50 °C). The dry thermoplastic composites exhibited similar fatigue performance to the thermoset counterpart at higher stress levels, with thermosets showing greater endurance at lower stress levels. Interestingly, the aged specimens showed comparable fatigue endurance, with a slight advantage in favour of the thermoplastic composites and less variability in their data. This study offers important insights into the fatigue performance of thermoplastic composites, emphasising their potential as sustainable alternatives to conventional thermoset composites for various marine applications.

Compression and hydrothermal ageing after impact of carbon fibre reinforced epoxy laminates

This paper proposes a new methodology for the assessment of seawater ageing effects on impact-damaged composite laminates. CF/Epoxy laminates which were unimpacted, and impacted at 30 J, 60 J, and 90 J by hemispherical and conical impactors were subject to 4 months hydrothermal ageing in renewed natural seawater at 60 +/-2 °C. The majority of water uptake by impacted laminates (0.05 wt% − 0.3 wt%) occurred in the first 24 h and is believed to be held in damage cavities by capillary mechanisms. The increase in diffusive water uptake rate by the matrix due to impact damage was only small, at less than 0.008 wt%.mm.hr−0,5, compared with the total diffusive water uptake rate of 0.1 wt%.mm.hr−0,5. Hydrothermal ageing reduced the residual compressive strength of pristine laminates by 25 % and impact-damaged laminates by 8 % to 16 % for impacts between 30 J and 90 J.

A feasibility study of using low-alkalinity seawater sea sand concrete to improve the long-term bond performance of the BFRP bar in the seawater environment

BFRP bar has been recognized as one of the most promising alternative reinforcements to address the chloride-induced corrosion of steel bar-reinforced concrete structures in the marine environment. However, the high alkalinity of normal concrete is aggressive to BFRP bars, affecting their long-term bond performance. To address this issue, the bond durability performance of BFRP bar-reinforced low-alkalinity seawater sea sand concrete (SWSSC) after aging in seawater was investigated using the central pull-out test. Scanning electron microscopy (SEM) was also used to characterize the microstructure of BFRP bar-SWSSC interfaces. The findings revealed that since the corrosion of BFRP bars in low-alkalinity SWSSC is substantially lower, the bonding durability performance of BFRP bar-reinforced low-alkalinity SWSSC is significantly higher than that of ordinary SWSSC pull-out specimens. After 270 days of accelerated aging in seawater at 55 °C, bond strength retention in normal SWSSC specimens reduces to about 73 %, whereas that of low-alkalinity SWSSC specimens improves to about 107–110 %. The energy consumption and carbon emissions of low-alkalinity SWSSC are less than half of those of normal SWSSC.

Influence of seawater immersion on acrylic adhesive properties and bond strength on wet composites

This paper describes a study on an acrylic based adhesive developed for marine repair applications. The adhesive alone was aged for over 12 months and tensile samples were tested periodically to characterize the influence of seawater aging at 40 °C. The adhesive alone plasticizes in seawater, losing around 40 % of both modulus and strength after 12 months, but these are largely recovered after drying. In parallel, adhesively bonded glass and carbon fibre composite assemblies were tested after similar aging times. Both retain over 80 % of unaged apparent shear strength after 12 months in natural seawater at 40 °C. Adhesive bonding of wet composite substrates, which had been immersed in seawater for up to 12 months before bonding, was also evaluated to determine residual bond strength. The break strengths of assemblies of wet glass fibre composites were not affected by substrate immersion for up to 12 months before bonding, while strengths of carbon fibre composite assemblies dropped to around 50 % after prolonged substrate immersion. Reasons for this difference are discussed. The results suggest that this adhesive shows good durability and should be considered for marine repair applications.

Mechanical Properties Characterization of Glass/Carbon Fiber Hybrid Multilayer Composite under Environmental Aging Condition

Metallic components in boating industry are being replaced with carbon fiber composites due to their light weight, excellent mechanical properties, and corrosion resistance. However, the carbon fiber cost has obstructed the substitution. Hybridization is suggested to merge carbon and glass fibers in cost-effective composites while maintaining the desired engineering properties. This study experimentally examines the impact of hybridization and seawater aging on the mechanical properties of glass and carbon fibers hybrid composites. A range of composites ([C]6, [CGC]s, [C]3[G]3, [GCG]s, and [G]6) are fabricated and aged in simulated seawater solution before their tensile, flexural, impact, and hardness properties are examined. The results revealed degradation in properties due to the ageing, the degree of degradation is influenced by the s hybridization configuration. The [G]6 sample shows the highest tensile strength reduction of 30% compared to 20% for the [C]6. The remaining samples exhibit reduction percentages falling between these two extremes. A similar behavior is observed in the flexural test, though the extremes values are smaller, 10.2%, and 12.5%. The impact and hardness tests showed an inverse relationship between the glass fiber content and impact strength degradation due to aging, while they exhibited a linear correlation for hardness degradation due to ageing.

Effect of seawater aging on mechanical, buckling, structural, and thermal properties of nano Al2O3 and TiO2‐doped glass‐epoxy nanocomposites

AbstractEnsuring the stability of composite structures in the marine environment is crucial. The harsh and corrosive nature of marine conditions presents unique challenges, making maintenance a top priority. In this study, the impact of seawater aging on the mechanical, buckling, structural, and thermal properties of glass fiber‐reinforced polymer nanocomposites was investigated. Composites were produced using the VARTM method with 2% nano Al2O3 and 2% nano TiO2. Aging was conducted in a seawater environment at room temperature for 120, 240, and 360 days. Mechanical properties, including tensile, compressive, flexural, impact, and buckling tests, were performed, and water absorption was determined. Structural analysis was carried out using SEM images. The experimental results indicated that the presence of nanoparticles minimized the effect of seawater. TiO2 preserved tensile strength by 10.33%, impact energy by 6.8%, and critical buckling load by 3.06% compared to the pure composite. Al2O3 reduced water absorption to 0.594% and preserved tensile strength by 6.67%, impact energy by 4.02%, and critical buckling load by 2%. Thermal test revealed an increase in thermal conductivity with aging, with the TiO2‐doped composite exhibiting the smallest increase (14.66%). The significance of the obtained results was confirmed through ANOVA analysis.Highlights Glass fiber‐reinforced nanocomposite was produced with nano Al2O3 and TiO2. The effect of seawater aging was investigated. It showed that TiO2 nanoparticles are a good candidate against seawater aging. The experimental results showed statistical significance.

Effect of seawater aging on the erosive wear response of aramid fiber reinforced composites

This study presents the effect caused by the saline environment (artificial seawater) on the physical and tribological properties of laminated composite materials reinforced with aramid fibers when they are subjected to erosive wear by sand particles. Composite materials made by epoxy resin and reinforced with glass fiber, carbon fiber and hybrid fiber (aramid with carbon) were studied. The laminates were superficially reinforced with layers of Kevlar fiber and prepared by the vacuum-assisted resin infusion process. The samples were subjected to a seawater accelerated aging process at 70°C for 1122 h. To reproduce erosive wear conditions of marine structural components, sea sand was used as solid particle under conditions of 4.5 bar of pressure, impact speed of 4.7 m/s and impact angle of 90°. The results showed that aged materials absorb more impact energy with respect to unaged counterparts, causing less material loss and a less depth in the wear track. The information generated by this research work may serve for the design and durability analysis of marine structures such as tidal turbine blades.

The Comparative Study of The Effectiveness of Seawater Aging with Traditional Techniques and Water Heater Technique for Salt Production

Salt is a product from marine resources which is a strategic commodity as an industrial raw material and food for the community. However, the condition of national salting is currently still not conducive, this is because salt production, both quantity and quality, is still insufficient and sufficient to meet national salt needs. This research aims to compare the effectiveness of traditional techniques and heating techniques in aging seawater for the seawater crystallization process in making salt. With this research, it is hoped that there will be the latest technological innovations to speed up the time for making salt with maintained quality, good quantity and profit so that national salt needs can be met. From this research it can be concluded that the use of heating techniques is more effective than traditional techniques because it can minimize the aging time of sea water and can increase the quantity of salt produced.

Influence of NR/EPDM Ratios on the Performance of Pneumatic Fenders in Seawater

The performance of pneumatic fenders in seawater is crucial to ensure safety and serviceability. Hence, the objective of this study is to investigate the performance of compound formulations of two different types of carbon black N660 and N220 at various NR/EPDM (Natural Rubber/Ethylene Propylene Diene Monomer) ratios of 100/0; 90/10; 80/20, and 70/30 in artificial seawater at 95°C for 30 days. The mechanical properties of rubber compounds were measured and compared before and after aging in seawater. Comparing two types of carbon black, no significant difference in tensile, elongation, tear strength, and compression set at the same blend ratios after aging in seawater. Nevertheless, the abrasion resistance of N220 is lower than that of N660 before and after aging in seawater due to insufficient dispersion. Adding high crystalline EPDM in the blend results in lower mechanical properties change than pure NR after aging in seawater. In addition, the blend contains EPDM imparts high abrasion resistance in seawater. Using EPDM up to 30 phr in the blend with NR indicates the possibility of utilizing this high oxidation stability of rubber as a pneumatic fender.

Evaluation of the Piezoresistive Response of GFRP with a Combination of MWCNT and GNP Exposed to Seawater Aging

Evaluation of the Piezoresistive Response of GFRP with a Combination of MWCNT and GNP Exposed to Seawater Aging

Effect of oxygen-containing functional groups on the micromechanical behavior of biodegradable plastics and their formation of microplastics during aging

Biodegradable plastics (BPs) are more prone to generate harmful microplastics (MPs) in a short time, which have always been ignored. Oxygenated functional group formation is considered to be a key indicator for assessing microplastic formation, while it is difficult to characterize at a very early stage. The micromechanical properties of the aging plastic during the formation of the MPs are highly influenced by the evolution of oxygen-containing functional groups, however, their relationship has rarely been revealed. Herein, we compared changes in the physicochemical properties of BPs and non-degradable plastic bags during aging in artificial seawater, soil, and air. The results showed that the oxidation of plastics in the air was the most significant, with the most prominent oxidation in BPs. The accumulation of carbonyl groups leads to a significant increase in the micromechanical properties and surface brittleness of the plastic, further exacerbating the formation of MPs. It was also verified by the FTIR, 2D-COS, AFM, and Raman spectroscopy analyses. Furthermore, the increased adhesion and roughness caused by oxygen-containing functional groups suggest that the environmental risks of BPs cannot be ignored. Our findings suggest that the testing of micromechanical properties can predicate the formation of the MPs at an early stage.

Taguchi analysis of the tensile behaviour of unaged and hygrothermally aged asymmetric helicoidally stacked CFRP composites

Taguchi method was used to predict and optimize the effects of hygrothermal aging on the tensile behavior of asymmetric helicoidally stacked Carbon Fiber Reinforced Plastic (CFRP) composites. This research is in furtherance to the previous work, which dealt purely with experiments. MR70 12P carbon fiber epoxy prepreg sheets were manufactured into laminated composites comprising constant inter-ply pitch angles ranging from 0o to 30o. The composites were tested in tension as either dry unaged specimens or following hygrothermal aging in seawater at the constant temperatures of 40 oC and 60 oC for 2000 hrs. Optimizations were conducted based on Taguchi L18 orthogonal array considering two design parameters viz. inter-ply stacking angles and hygrothermal aging temperature. The result depicted that the combination of aging temperature (C) and stacking angles are major factors in determining the tensile behavior of composite materials (p = 0.011). The model explains 86.6% of tensile strength variability, with a predicted R-squared value of 93.04%. The model’s robustness is supported by the adjusted R-squared value of 77.6%. Analysis of variance shows that inter-ply stacking angles are the main significant factor affecting the tensile behaviors at a 95% confidence level. A confirmation test was carried out to validate the optimized results and it was found that there were improvements in S/N ratios from initial to optimal setting.

Highly efficient underwater acoustic absorber designed by filled-microperforated plate-like structure: Aging and life prediction

The underwater sound absorption material for submarines should fulfill the demand for remarkable performance in medium-low frequency sound absorption at low thicknesses. Hence, in this paper, the innovative “filled-microperforated plate-like” (F-MPPL) structure was introduced to the hollow microballoons filled underwater sound absorption composite (HBF composite) using the tailor-made 3D spacer fabric. The test results show remarkable mechanical properties with a compression strength and compression modulus of 2256 KPa and 14.6 MPa for the new type of F-MPPL composite, respectively. In addition, the peak sound absorption coefficient of the F-MPPL composite reaches 0.77 at just 7.5 mm thickness based on the resonant sound absorption characteristic introduced by the F-MPPL structure. Moreover, the study investigated the effects of seawater aging on the F-MPPL composite and found that while there was a decrease in compression strength and average sound absorption coefficient, the degradation of the F-MPPL composite was significantly smaller than the HBF composite due to the inhibitory effect of spacer yarns on pore expansion. Finally, this study proposed the method of using compression strength to predict the long-term life of the F-MPPL composite under seawater aging, and a 60% retention rate after 20 months was displayed.