Seawater Aging Research Articles

Hydro-elastic interaction of polymer materials with regular waves

The use of flexible materials has the potential to offer a step-change reduction in the cost of wave energy devices by enabling them to absorb more extreme wave loads through their structural responses. Flexible wave energy converters are often manufactured from polymer, fabric, or reinforced polymer components. The elastic modulus, fatigue performance, seawater ageing, and manufacturing process determine the effectiveness of flexible components at replacing their rigid counterparts. During design, it is necessary to assess the hydrodynamic response of the WEC structure to different wave conditions. This work investigates the hydro-elastic response of a submerged polymer membrane, held in a horizontal frame, exposed to regular wave loading. Fast-Fourier Transform analysis enabled assessment of the non-linear response of the membrane exposed to the different wave conditions. The ratio of harmonic to measured wave amplitude ratio gives insight into the excitation mode of the membrane as a function of frequency. It is found that the peak response of the membrane tends to coincide with the fundamental frequency of regular waves. By varying the ratio of membrane length to wavelength an understanding is provided of the hydro-elastic response of the polymer membrane which should be useful in validating software used in the design of flexible WECs.

Marine Applications of Fiber-Reinforced Polymer Matrix Composites

Composite materials are formed by bringing together two or more materials that are insolublein each other at a macro level. Composites consist of two main elements such as reinforcement (thecarrier) and matrix (the binder). These materials are generally classified according to matrix andreinforcement elements. In the classification made according to the matrix element, polymer, metal, andceramic matrix composites are examined. In this classification, polymer matrix composites are widelyused in practice. A polymer matrix from the thermoset or thermoplastic group is reinforced with varioustypes of continuous or short fibers. Composites belonging to this group are widely used in basic sectorssuch as automotive, aviation, and marine. Especially in the marine sector, polymer matrix composites areused in the construction of marine vehicles (ships, boats, yachts, etc.) and equipment. Marine systems andstructures include the hull and shipbuilding industries (ship and submarine masts, propellers, and interiorparts), the offshore applications industry (gas pipelines, tendons, and support structures), and therenewable energy sector (turbine devices and rotor blades). The importance of lightweight design isincreasing day by day in vehicles used in land, air, and sea transportation. Today, the increase in the valueof both safety and energy savings causes research on composite materials to intensify in the marinesector. It is advantageous to use composite materials in many parts so that negative environmental effectssuch as corrosion, biological pollution, seawater aging, and hydrostatic pressure cause minimal damage tomarine structures. With the developments in composite science, the level of use of these materials isincreasing in the marine sector, as in every other field. This review presents an overview of the use ofpolymer matrix composites in the marine industry.

An experimental study on the hydrothermal aging effect on the free vibration properties of hybrid aramid/glass/epoxy composites: Comparison of sea water and distilled water

AbstractThe purpose of this experimental work is to investigate the impact of hydrothermal aging on the viscoelastic characteristics of hybrid aramid/glass/epoxy composites. In addition to the hybrid composites prepared by vacuum infusion method in two different hybrid configurations ([G3A3]S, [A3G3]S) and two non‐hybrid composite groups ([G6]S, [A6]S) were included for comparison purposes. Composite samples were kept in 4 different aging environments (distilled water 25°C, distilled water 70°C, seawater 25°C, and seawater 70°C) for 6 weeks. To assess the dynamic properties (natural frequency and damping ratio) of composites, a free vibration test was conducted. The vibration test results of the samples were calculated by the half‐power bandwidth method. The results revealed that hydrothermal aging did not have serious effects on first‐mode natural frequency. It was observed that the damping ratios of hybrid composites increased after hydrothermal aging when compared with unaged samples. The results from dynamic aspects like the storage modulus and loss modulus were consistent among themselves. The parameters of the storage modulus and loss modulus have both decreased as a result of hydrothermal aging. In addition, the results proved that the rise in temperature accelerated the degradation in mechanically deteriorated composite materials. It was also found that aging in seawater was induced to more deterioration of hybrid and non‐hybrid composite materials.Highlights The order of the fabrics play an important role in free vibration properties of hybrid composites. Aging hybrid composites at different temperatures affects their free vibration properties. and values decreased more as the temperature increased. Hydrothermal aging has increased the dumping ratio values of composite materials.

Respiration Patterns in the Dark Ocean

AbstractIn the dark ocean, respiring organisms are the main sink for dissolved oxygen. The respiration rate in a given seawater volume can be quantified through dissolved oxygen drawdown or organic matter consumption as a function of time. Estimates of dissolved oxygen utilization rates (OUR) abound in the literature, but are typically obtained using proxies of questionable accuracy, often with low vertical resolution, and neglecting key regions such as the Southern and Indian oceans. Respiration rates based on particulate (POC) or dissolved (DOC) organic carbon are also sparsely observed and for DOC are unavailable in many regions. Consequently, the relative contributions of POC or DOC as a respiration substrate in the dark ocean are unknown. Here, we use recent datasets of true oxygen utilization, seawater age, and DOC to derive OUR and DOC consumption‐rate profiles in 10 oceanic regions. We demonstrate that although DOC and POC consumption rates are globally consistent with OUR, they underestimate OUR in the deep, suggesting strong oxygen utilization at the seafloor. In the abyss, we find a negative correlation of the DOC consumption rate with seawater age, suggesting that DOC reactivity decreases along the deep branch of the conveyor circulation. Our results highlight that benthic organisms are sensitive to perturbations in the surface production of organic matter and to large‐scale circulation changes that affect its supply to the abyss.

Comparative experimental study on mechanical properties of CFRP subjected to seawater and hydrostatic pressure

Composite structures used in marine environments experience the erosion of seawater ageing and alternating water pressure during floating and diving. In this paper, the mechanical behavior of CFRP laminates under seawater pressure environment was studied experimentally. The evolution process of moisture absorption behavior and erosion defects in the cross section was monitored. The mechanism of the influence of hydrostatic pressure on the in-plane and interlaminar failure modes of the specimens was revealed. The results demonstrate that the hydrostatic pressure can activate the capillary action at the interface between the fiber and the matrix, and the plasticization of the matrix significantly reduces the in-plane strength of the specimens (the tensile strength decreases by 28.3%). As the pressure increases the specimens are more susceptible to delamination failure in the compression area under bending load. The toughening and embrittlement mechanisms of the specimens were activated simultaneously, with a minor increase in GIC and a slight decrease in GIIC under hydrostatic pressure. A short-term pressure dependent nonlinear model for predicting mechanical degradation was established based on the Arrhenius equation. The fitness of proposed model was compared with other models from the literature to verify the accuracy of the prediction.

Recycling and ecotoxicity of flax/PLA composites: Influence of seawater aging

Poly(lactic acid) is finding increasing applications as it is a bio-sourced compostable thermoplastic. Its properties can be improved by adding flax fibres, which are also compostable. The possibility to recycle the composite after service is attractive because it reduces waste in landfills, is a cost-effective measure to reduce the need for raw materials and extends the life span of composites. However, few reports are available to verify how recycling affects properties of flax-PLA composites. In addition, if these recycled materials are to be used in marine applications, it is important to investigate whether they will be adversely affected by seawater compared to virgin materials, as well as to investigate the toxicity of these materials for marine organisms. The goal of this work was to address these three points, i.e., to assess whether recycling and posterior environmental weathering (seawater exposure) changes the flax-PLA composite properties, and to assess these materials’ toxicity for biota (a benthic copepod species, Nitokra spinipes). First, our results indicate that recycling up to four times hardly affects the composite properties. However, immersion in seawater at 40 °C for up to nine months reduces tensile strength of both virgin and recycled composite by up to 60%. Finally, the ecotoxicity evaluation indicated that neither leachates from PLA nor from Flax-PLA induce immobilization of N. spinipes, nor were any immobilization effects induced by leachates resulting from materials aged for two months in seawater. These results will contribute to assessing the sustainability of future bio-based polymer applications.

Seawater ageing of thermoplastic acrylic hybrid matrix composites for marine applications

Increasing usage of polymer composite materials necessitates the development of recyclable alternatives to traditional thermoset matrices or new techniques for recycling these materials. One family of promising recyclable matrices are the room temperature infusible acrylic resins, known commercially as Elium®. If these new materials are to be used in the tidal stream energy and shipping sectors, they must be able to withstand long-term immersion in seawater without significant losses in mechanical properties. In this study, accelerated seawater ageing is applied to acrylic/glass fibre and modified acrylic/glass fibre composites along with a traditional epoxy/glass fibre baseline. The mechanical properties (tensile, flexural, and short beam) are compared before and after ageing, and electron microscopy is used to examine fracture surfaces to determine the effects of water ingress on fracture propagation. In addition, the diffusion coefficients of the composites in seawater are compared and the changes in glass transition temperatures are used to determine the effects of plasticisation.

Degradation of high density polyethylene packaging by accelerated aging in sea water

AbstractThe increase of plastic waste in the marine environment raises several ecological, human, and biological problems. In this work, an accelerated artificial aging study was conducted in seawater after immersing samples of high‐density polyethylene bottles for several aging times and at three different temperatures. The deterioration of the mechanical properties of High density polyethylene (HDPE) under different aging conditions was investigated using tensile and compression tests. The absorption of seawater by the samples was analyzed using a gravimetric method and Fourier transform infrared spectrometry (FTIR). Further surface analysis of the samples during accelerated aging was performed using a scanning electron microscope. The results show that HDPE loses its ductility and rigidity. FTIR analysis confirms the increase in crystallinity during aging.

Surface structures changes and biofilm communities development of degradable plastics during aging in coastal seawater

Biodegradable plastics (BPs) are a suitable alternative to conventional plastics. Still, their excessive or unplanned use may disrupt the abundance and community structure of the microbial population. To this end, a 58-day experiment in which biodegradable plastic objects, such as bags and boxes, were exposed to near-coastal seawater was conducted. They also assessed how they affected the diversity and organization of bacterial populations in seawater and on the surface of BPs products. It is evident that after the exposure time, both BP's bag and box products deteriorate in the ocean to varying degrees. The results of high-throughput sequencing of bacterial communities in seawater and those colonized on BPs products reveal significant differences in microbial community structures between seawater and BPs plastic samples. These suggest that the degradation of biodegradable plastics is shadowed by microorganisms and exposure time, while BP products influence the structural characteristics of microbial communities.

Comparison between discarded facemask and common plastic waste on microbial colonization and physiochemical properties during aging in seawater

Facemasks are indispensable for preventing the spread of COVID-19. However, improper disposal of discarded facemasks has led to their contamination in the marine environment. To understand the environmental risk of this emerging plastic pollution, it’s important to clarify the features that distinguish discarded facemasks from common plastic waste during aging. This study compared the microbial colonization, degradation-related enzymes, and physicochemical properties among surgical masks, polystyrene cups, polycarbonate bottles, and polyethylene terephthalate bottles in their aging processes in natural seawater. Compared to the other plastic wastes, surgical masks were colonized by the most diverse microorganisms, reaching 1521 unique prokaryotic OTUs after 21-day exposure in seawater. Moreover, the activity of eukaryotic enzymes associated with plastic degradation was 80-fold higher than that in seawater, indicating that the colonized eukaryotes would be the major microorganisms degrading the surgical masks. Meanwhile, the nano-sized defects (depth between 8 and 61 nm) would evolve into cracks of bigger sizes and result in the breakage of the microfibers and releasing microplastics into the ocean. Overall, our study demonstrated a distinctive plastisphere occurred in surgical masks from both microbial and physiochemical aspects. This work provides new insights for assessing the potential risk of plastic pollution caused by the COVID-19 pandemic.

Effect of aging on the in-plane and out-of-plane mechanical properties of composites for design of marine structures

This paper describes an approach allowing aging to be included in the design of marine structures. Two types of aging are considered, physical aging and seawater saturation. The latter is shown to be more severe for this material, with losses in properties of up to 30% being measured after aging. A complete set of in-plane and out-of-plane properties was generated for a carbon/epoxy composite, and these were then used as input data to model the response of a flexural beam under a mixed shear/bending load. Reasonable agreement is found between model and test results; both show the strong influence of seawater conditioning on the composite performance, with a reduction in strength after aging of around 35%. This approach can be applied to account for seawater aging during the design of composite structures.

Photo- and Water-Degradation Phenomena of ZnO Bio-Blend Based on Poly(lactic acid) and Polyamide 11.

The goal of this work was to investigate the morphological and chemical-physical changes induced by adding ZnO nanoparticles to bio-based polymeric materials based on polylactic acid (PLA) and polyamide 11 (PA11). Precisely, the photo- and water-degradation phenomena of nanocomposite materials were monitored. For this purpose, the formulation and characterization of novel bio-nanocomposite blends based on PLA and PA11 at a ratio of 70/30 wt.% filled with zinc oxide (ZnO) nanostructures at different percentages were performed. The effect of ZnO nanoparticles (≤2 wt.%) within the blends was thoroughly explored by employing thermogravimetry (TGA), size exclusion chromatography (SEC), matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and scanning and transmission electron microscopy (SEM and TEM). Adding up to 1% wt. of ZnO resulted in a higher thermal stability of the PA11/PLA blends, with a decrement lower than 8% in terms of molar masses (MMs) values being obtained during blend processing at 200 °C. ZnO promoted trans-ester-amide reactions between the two polymers, leading to the formation of PLA/PA11 copolymers. These species could work as compatibilisers at the polymer interface, improving thermal and mechanical properties. However, the addition of higher quantities of ZnO affected such properties, influencing the photo-oxidative behaviour and thus thwarting the material's application for packaging use. The PLA and blend formulations were subjected to natural aging in seawater for two weeks under natural light exposure. The 0.5% wt. ZnO sample induced polymer degradation with a decrease of 34% in the MMs compared to the neat samples.

The coupling effects of seawater aging and fatigue micro-crack on mechanical degradation of carbon fiber/epoxy plain woven composites

Carbon fiber reinforced plastics applied in the marine industry are often exposed to conditions of seawater and alternating loads for extended periods, which can cause the complex degradation process of the composites. In this work, the coupling effects of micro-cracks and the seawater aging on the carbon fiber/epoxy resin-based plain woven composites were experimentally investigated. The micro-cracks were introduced into the composites through the three-point bending fatigue load. The results indicate that the residual stress generated by different expansions between carbon fiber and epoxy resin that reduces the interfacial properties of the composite is the primary reason for seawater aging. Besides, seawater aging causes the bending strength of the specimens with fatigue damage to decrease more seriously than that of the undamaged specimens. This is because micro-cracks increase the specific surface area of the composites in contact with seawater to provide channels for seawater diffusion. The coupling effects suggest the maintenance cycle of the composite parts should be gradually reduced if micro-cracks occur in some composites.

Degradation and lifetime prediction of thermoplastic polyurethane encapsulants in seawater for underwater acoustic sensor applications

Degradation of thermoplastic polyurethane (TPU) encapsulants used in an underwater acoustic sensor (UAS) was examined by aging in seawater, and the lifetime of TPU encapsulants was estimated using an empirical approach based on accelerated lifetime test (ALT). The TPU encapsulants were placed in seawater and aged at temperatures of 85, 100 and 110 °C. TPU encapsulants underwent a hydrolysis reaction during aging in seawater, changing the chemical structure and molecular weight of TPU. Molecular dynamic (MD) simulation results described the hydrolysis degradation of TPU results in the decrease in tensile strength. Tensile tests were conducted on the aged TPU encapsulants, and then failure times for each of the accelerated conditions were estimated from the changes in tensile strength over aging time. The accelerated failure times were used for the lifetime prediction of TPU encapsulants at a use-stress level by using ReliaSoft's ALTA software. An empirical prediction model based on Arrhenius equation and Weibull distribution was determined for the lifetime prediction of the TPU encapsulant, facilitating lifetime estimations of TPU encapsulant at various failure criteria. A decrease in the tensile strength to 50% of the initial value was established as the failure criterion for lifetime prediction, indicating that half of TPU encapsulants will fail after aging about 20 years. Therefore, this result helps to determine the appropriate time for replacement of TPU encapsulant before failure.

Seawater aging effect on fiber-reinforced polymer composites: Mechanical properties, aging mechanism, and life prediction

Fiber-reinforced polymer (FRP) composites are widely used in marine engineering fields, such as coastal construction, offshore bridges, submarines, and warships, owing to their light weight, high strength, and corrosion resistance. However, owing to the harsh marine environment, FRP composites used in the ocean are inevitably affected by seawater aging. Therefore, it is necessary to investigate the seawater aging properties of FRP composites. In this study, the seawater aging mechanism of FRP composites is summarized, and the influence factors (matrix type, fiber type, immersion temperature, loading mode, and aging method) of seawater aging on the mechanical properties of FRP composites are further reviewed in detail. Based on this, the method for improving the seawater resistance of FRP composites is summarized. In addition, the research schemes of accelerated aging of FRP composites and commonly used life prediction models are summarized, and the methods and suggestions for improving the accuracy of life prediction are further discussed.

New Perspective on the Mobilization of Microplastics through Capillary Fringe Fluctuation in a Tidal Aquifer Environment

The presence of plastic fragments in the environment is a growing global concern. In this study, we explored the effects of dynamic fluctuations of capillary fringe on the transport of microplastics (MPs) in the substrate combining various environmental and MP properties. Both experimental and Hydrus-2D modeling results confirmed that increasing cycles of water table fluctuation led to the rise of capillary fringe. An increase in the cycles of water table fluctuations did not significantly change the overall MP retention percentages in 0.5 mm substrate but altered the MP distribution along the column. In 1 and 2 mm substrate, the increase in cycle numbers enhanced the MP transport from substrate to the water below. In terms of the size of the MPs, more 20-25 μm polyethylene (PE2) were retained in the substrate compared to 4-6 μm polyethylene (PE1) under the same number of fluctuation cycles. High-density polytetrafluoroethylene (PTFE, 5-6 μm) exhibited higher retention percentages compared to PE1 particles. Ultraviolet aging for 60 days enhanced PE1 transport along the column, while 60 days of seawater aging did not affect PE1 transport greatly. For PTFE, ultraviolet and seawater aging enhanced its retention in the substrate. The retention percentages of both PE1 and PTFE in the column increased with the elevated ionic strength and the decrease of fluctuation velocity. This work highlights that capillary fringe fluctuation can serve as a pathway to relocate MPs to the tidal aquifer.

Aging Characteristics and Ecological Effects of Primary Microplastics in Cosmetic Products Under Different Aging Processes.

Microplastics are becoming an increasingly environmental concern, but only a few studies have focused on primary microplastics. Herein, four primary microplastics (Lapis, Jade, Topaz and White) commonly used in cosmetic products were selected to investigate the effects of sunlight, seawater, and soil aging on their environmental behaviors. After sunlight and seawater aging, the surfaces of all four microplastics developed breaks and cracks, with particle sizes decreased and specific surface areas increased. Topaz exhibited the most significant changes under sunlight and seawater aging and its maximum adsorption capacity of phenanthrene significantly increased by 22.50% and 47.86%, respectively. Under soil aging, amending with either White or Topaz changed the soil bacterial community composition and diversity, but they had less ecological impacts than polyvinyl chloride plastic. The results of this study provide vital information for understanding the aging characteristics, environmental behavior, and ecological effects of primary microplastics under natural aging processes.

Study of Mechanical and Thermal Properties for Epoxy Grouts Subjected to Seawater Conditioning at Elevated Temperature: Tensile Test and Compressive Test

Pipelines and risers are major transportation of oil and gas. These components are often exposed to extreme marine environmental conditions that can cause pipelines to fail due to corrosion. Hence, epoxy grouts are used as a coating material on the surface of pipelines and risers for supporting the pipe structure and corrosion prevention. In this case, the efficiency of epoxy grout is important in pipeline rehabilitation. Research on the adaptation of seawater, temperature, and epoxy grouts is carried out to determine the changes in mechanical and thermal properties of the material. The preparation of epoxy grouts was prepared with a mixture of epoxy resins, epoxy hardeners, and aggregates. After the sample compounds have been flattened, the mixture will be put into the mold. The seawater aging process was performed for seven days before conducting laboratory experiments. After the seawater aging process, there were physical changes on the surface of the epoxy grouts which are the epoxy grout become harder and there were voids that can act as stress concentration points that may cause micro-crack on the specimen. Next, tensile (ASTM 638) experiments were performed at different temperatures of 27°C, 40°C, 52°C, 72°C, 80°C and 100°C while the result of compression experiment is based on the literature critique of past journals. Based on the result, the young modulus and ultimate tensile strength of the epoxy grouts are decreased with increasing temperature. The increment of temperature causes the epoxy grouts to become weaker due to the changes in the polymer matrix structure of the epoxy grouts which lead to the failure at low load and shortens the life of the material. In addition, epoxy grouts are amorphous materials where the glass transition temperature determine the mechanical and physical properties of epoxy grouts. Therefore, the results of the study found that the epoxy grouts changed its mechanical properties from brittle to ductile when the temperature is at 72°C. From the comparison between samples immersed and not immersed in seawater, there is a decrease in Young’s modulus, ultimate tensile stress and strain due to the effect of seawater reaction. In conclusion, the increment in temperature and seawater adaptation factors affect the strength and durability of epoxy grouts.

Development of a low-alkalinity seawater sea sand concrete for enhanced compatibility with BFRP bar in the marine environment

To enhance the durability performance of Basalt Fiber Reinforced Polymer (BFRP) bar reinforced Seawater Sea Sand Concrete (SWSSC) structure components in the marine environment, this paper investigated the feasibility of reducing SWSSC alkalinity to improve its compatibility with BFRP bars. The low-alkalinity ternary mixtures were designed with ordinary Portland cement (OPC), silica fume (SF) and fly ash (FA) through the simplex centroid design method. The evolutions of micro-morphology and hydration phase were characterized by isothermal calorimeter, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and thermogravimetric analysis. The added SF and FA inhibit the formation of AFm phases and Friedel's salt, and consume the Portlandite content in seawater cement paste. Exposure in the marine environment can lead to magnesium and sulfur abundant zonation in the low-alkalinity SWSSC. The durability performances of BFRP bars reinforced SWSSC columns are evaluated through accelerated aging tests in a simulated marine environment at 55 °C. The tensile strength degradation of BFRP bars embedded in low-alkalinity SWSSC is significantly mitigated due to the less alkaline and less moist internal environment. After 180-day accelerated aging, the tensile strength retentions of BFRP bars wrapped by low-alkalinity and normal SWSSC are higher than 70% and less than 24%, respectively. After accelerated aging in seawater, the load-bearing capacity of BFRP bars reinforced low-alkalinity SWSSC column slightly improves and the ductility remains unaffected. Meanwhile, the ductility of BFRP bars reinforced normal SWSSC column is reduced by about 30% after conditioning. The research outcomes can serve as a solid base for the durability design of BFRP-SWSSC structures in the marine environment.

Effect of seawater immersion on the drill induced delamination failure in glass fiber reinforced polymer composites – Experimental and statistical analysis

Composite materials, particularly glass fiber reinforced polymer (GFRP) composite, have established a strong presence in the marine industry. Its marine applications range from constructing massive naval vessels to constructing simple fishing boat hulls. Previous research has established that seawater aging has a detrimental effect on the physical and mechanical properties of GFRPs. Additionally, drilling composites are known to cause delamination damage, resulting in a high failure rate. Since composite components are assembled with fasteners, drilling operations are unavoidable. Thus, the current study examines the effect of seawater aging at a macroscopic level while considering the input parameters spindle speed and feed and material thickness and the response variables as peel-up and push-down delamination damages. The result indicated higher failure rates in the seawater-treated composites than in untreated composites. The maximum damages were seen in the 60 days of immersed composites, wherein the peel-up delamination damage increased by 290.22, 305.86, and 250.81 %, and the push-down delamination damage increased by 69.48, 76.38, 64.28 % in 6, 8 and 10 mm composites, respectively. The combinational effect of seawater degradation of GFRP composites and the damages caused by the cutting forces (function of speed and feed) attribute to the failure rate increase concerning the drilling-induced delamination damages in the composites. In addition to investigating the effect of seawater immersion on damages, the study also provides the regression analysis-based mathematical model having high goodness of fit and predicting capability to determine the damages for the given values of input variables.