Effects of hygrothermal and salt mist ageing on the properties of epoxy resins and their composites

doi:10.21203/rs.3.rs-1876022/v1

Download PDF

Research Article

Effects of hygrothermal and salt mist ageing on the properties of epoxy resins and their composites

https://doi.org/10.21203/rs.3.rs-1876022/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Epoxy resins have a wide range of outdoor applications wherein they are affected by ageing. In this study, the ageing of epoxy resins and their carbon fibre reinforced composites was artificially accelerated under hygrothermal and salt mist conditions. The moisture penetration along the depth, water absorption, appearance, hardness, the density of the epoxy resins, and the variation pattern of impact strength and tensile strength of the epoxy-based composites were investigated. The ageing mechanisms were explored using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Both the ageing modes had essentially similar influences on the properties of the resins and their composites and did not significantly affect the chemical structure, thermal decomposition properties, and microstructure of the epoxy resin, with physical adsorption of water primarily observed during the ageing process. Though the water penetration rate in salt mist ageing was slightly higher than that in hygrothermal ageing in the early ageing stage, it was essentially the same in the later stage. The absorbed water during the ageing process caused micro-cracks at the interface between the fibres and the resin weakening the interfacial strength and reducing the mechanical properties of the composites.

Polymer-matrix composites (PMCs)

Environmental degradation

Moisture

Pultrusion

moisture absorption

Epoxy resins exhibit remarkable mechanical properties, electrical insulation properties and chemical resistance. Epoxy resins have been widely used in construction, automotive, electronics, packaging, textiles, medical, and sports industries, owing to their advantages, such as low cost and simple processing and moulding procedures. Moreover, epoxy resin-based composites have gradually replaced traditional metal materials in some engineering applications due to their light weight, high strength, and workability, finding applications in a variety of fields such as aerospace, wind turbine blades, and watercrafts [1–4].

However, during the practical applications of epoxy-based composites, especially outdoor applications, such as offshore wind turbine blades and ship hulls, these materials inevitably undergo ageing due to the influences of environmental factors, such as temperature, humidity, salt mist, and ultraviolet light[5–8]. These factors lead to degradation of material performance or even failure, reducing the reliability and safety of the products and resulting in huge economic losses.

A series of studies have been conducted on the ageing behaviour of epoxy resin-based composites. It was found that the mechanical properties of composites were reduced in hygrothermal and salt mist environments, primarily due to moisture absorption[5, 8–10]. The materials showed reduced stiffness due to moisture absorption and plasticisation of the epoxy resin matrices[11–13]. Moreover, the thermal expansion coefficients of the epoxy resins and reinforcing materials were different. Consequently, this generated internal stress in the composites during ageing and formed microscopic defects within the material, resulting in inferior mechanical properties. The hygrothermal environment also influenced the glass transition temperature of epoxy resin-based composites [14–16], while the dielectric constant and dielectric loss of the composites changed with an increase in ageing time [17, 18]. The ageing properties of epoxy resin composites primarily result from the ageing of the resin matrix and the ageing of the composite interface; therefore, the ageing properties of epoxy resins and their composites need to be studied simultaneously.

Currently, many applications demand high performance from epoxy resins and their composites over long time periods, under relatively adverse conditions such as high temperature, high humidity, and salt mist. Therefore, examining the ageing behaviour of epoxy resins and their composites is crucial for safe and appropriate use and storage of the composites. At present, few studies present a concurrent investigation on the ageing of epoxy resins and epoxy resin-based composites. The research on the ageing performance of epoxy resins is mainly focused on coatings or other thin-layer products, lacking insight into the performance of comparatively thick epoxy resins across the thickness[2], especially epoxy/anhydride system. With the technological development of composite materials, epoxy resins and their composites have been transitioning into larger and thicker products. Hence, the study of ageing performance and ageing patterns of epoxy resins and relevant composite materials with certain thicknesses is critical to ensure the safety and promotion of composite products.

This research compared the moisture absorption behaviour of epoxy resins across the thickness and the changes in physical properties, thermal properties, chemical structure and microstructure under artificially accelerated hygrothermal and salt mist ageing conditions. We investigated the evolution of mechanical properties and microstructure of carbon fibre/glass fibre hybrid reinforced epoxy resin pultruded composites to explore the ageing pattern of epoxy resins and their composites, thereby laying a foundation for the manufacturing and safe applications of composite materials. It's important to note that besides humidity and salt studied in this research, other factors, such as temperature[19], pH[14], stress state[20], void contents[21], fiber orientation[22] and volume fraction[23], have a coupling effect on the aging properties of epoxy and its composites

2.1. Materials

Epoxy resin with multi-functional groups and anhydride curing agent were purchased from Dow Chemical Company, USA. Six-membered heterocyclic benzo compounds, the toughening modifier of “sea-island” structure, defoamer, release agent and other reagents were developed at the Carbon Fibre Engineering Technology Research Centre of Shandong University, China. Carbon fibre (T700-12K-50C) was procured from Toray Industries, Inc., Japan. High-strength glass fibre tape was purchased from Shandong Lufa Carbon Fibre Composites Co., China. Other reagents, namely, sodium chloride, anhydrous ethanol and acetone were commercially purchased in China.

2.2 Sample preparation

2.2.1 Preparation of epoxy resin castings

Epoxy resin, curing agent, modifier, and defoamer were mixed in certain proportions to form a gel with a viscosity of approximately 300 ~ 500 mPa·s (25 ℃). The gel was then poured into a mould and moulded into a 3 mm-thick board through a series of processes including vacuum defoaming, curing, cooling, and demoulding. The resulting epoxy resin board was cut into sample strips. The epoxy resins used in the hygrothermal ageing and salt mist ageing study were cut from the same casting board to ensure uniformity in performance and colour. The resin curing conditions were 80°C/1 h + 100°C/2 h + 160°C/2 h.

2.2.2 Preparation of carbon fibre/glass fibre hybrid reinforced epoxy pultruded composites

Composite rods with a diameter of 7.5 mm were prepared using a pultruding process. The epoxy resin used to prepare the composites was the same as that used in the preparation of epoxy castings. The reinforcing fibres included internal unidirectional T700 carbon fibre and external high-strength glass fibre cloth, with a fibre content of 60% by volume. The process, schematically shown in Fig. 1, is as follows: the carbon fibres and glass fibre tape were impregnated in an epoxy resin gel solution under the force of a pulling machine and were then cured in a mould. The curing temperature was 150 ~ 200°C and the pultrusion speed was 500 mm/min. The epoxy and its composite have been used in heat resistant aluminum alloy composite core conductor [24].

2.3 Experimental methods

2.3.1 Hygrothermal ageing

Hygrothermal ageing experiment was carried out according to the Chinese standard test “Determination of the effects of humidity and heat, water spray, and salt mist on plastics” (GB/T 12000 − 2003), with alternating high and low temperature hygrothermal ageing conditions of (25 ± 3) °C × 12 h (humidity not less than 95%) and (55 ± 1) °C × 12 h (humidity maintained at (93 ± 3) %), respectively.

2.3.2 Salt mist ageing

The salt mist ageing test was also carried out in accordance with the Chinese standard test “Determination of the effects of humidity and heat, water spray, and salt mist on plastics” (GB/T 12000 − 2003), with salt mist ageing conditions shown in Table 1.

Table 1

Salt mist ageing conditions
One ageing cycle (h)	Ageing temperature (°C)	Concentration of NaCl solution (g/L)	pH
24	35 ± 2	50 ± 5	6.5 ~ 7.2

2.3.3 Ageing time

Epoxy resins and their composites were subjected to salt mist ageing and hygrothermal ageing for the same duration of time. The epoxy resin castings were aged for 12 h, 24 h, 36 h, 48 h, 72 h, 96 h, 144 h, 192 h, 240 h, 336 h, 456 h, 576 h, 720 h, 912 h, 1104 h, 1344 h, 1584 h, 1872 h, and 2160 h. The epoxy pultruded composites were aged for 48 h, 96 h, 144 h, 240 h, 336 h, 432 h, 576 h, 720 h, 960 h, 1440 h, 2160 h, 3120 h, 4080 h, and 5280 h.

2.4 Characterisation methods

An electronic balance with an accuracy of 0.1 mg was used to measure the rate of change in mass of the epoxy resin castings. The resin density was measured using the buoyancy method. A microscope and a camera were used to observe the depth of water penetration and change in colour of the epoxy resin castings. A Richter hardness tester (AR936, Sigma Technology) was used to determine the hardness of the epoxy resin. Structural changes in the epoxy resin castings were examined via Fourier transform infrared spectroscopy (VERTEX-70, Bruke). Thermal decomposition of the epoxy resin was analyzed using a thermogravimetric analyser (Instrument/SDT-Q600, TA) under the following conditions: heated under nitrogen purge, from 25°C to 800°C at a rate of 10°C/min. The microstructural and morphological characterisation of the epoxy resins and their composites was carried out using a scanning electron microscope (SEM, SU-70, Hitachi). A universal testing machine (CMT4204, Shenzhen Sans Testing Machine Co., Ltd.) was used to perform the three-point bending test on the composites: the loading speed was 2 mm/min, the length of test samples was 120 mm, and the support span was 60 mm. An impact tester (XJJ-50) was used to perform an unnotched impact test on the epoxy resin-based composites with a pendulum energy of 15 J and a support span of 55 mm.

3.1 Ageing properties of epoxy resin castings

3.1.1 Moisture absorption

Figure 2 shows the mass variation rates under hygrothermal ageing and salt mist ageing conditions, and the corresponding fitted curves. Both the curves follow a similar trend. In the early stage of ageing, the mass variation rate (Mt) was almost a linear function of the square root of moisture absorption time (t^1/2) and the moisture absorption rate was relatively high. However, with an increase in the ageing time, the moisture absorption rate gradually decreased and eventually saturated. The moisture absorption rate in salt mist ageing was slightly higher than that in hygrothermal ageing. However, the final moisture absorption rate at saturation was approximately 1.1% under both the conditions.

Figure 3 shows cross-sectional images of the epoxy resins at different ageing times. The change in colour of the resin edges can be clearly seen. As the ageing time increased, distinct light-coloured 'bands' appeared around the edges of the epoxy cross-section and the widths of the bands gradually increased. The width of the band indicates the depth of water penetration. As can be seen from Fig. 3, the bands appeared earlier in salt mist ageing, at 192 h, whereas they appeared at 240 h in hygrothermal ageing. This indicates that the rate of moisture absorption by the epoxy resin in salt mist ageing was slightly higher than that in hygrothermal ageing. After 2160 h, the band widths under the two ageing modes were essentially similar, at 0.282 mm (hygrothermal) and 0.272 mm (salt mist), indicating that the saturation moisture absorption rates of the epoxy resin in both modes were essentially the same. This is consistent with the results of moisture absorption rate test in Fig. 2.

Figure 4 shows the changes in colour of the epoxy resin before and after ageing. As the ageing time increased, the colour of the epoxy resin gradually faded, changing from yellowish brown to light white; this can be attributed to the scattering of light by the water molecules absorbed in the resin. The colour change in the salt mist aged samples occurred earlier (at 144 h) than that in the hygrothermal aged samples (at 192 h). This confirms that the moisture absorption rate in the salt mist aged samples is slightly higher than that in hygrothermal aged samples.

3.1.2 Density

The change in density of the epoxy resins at different ageing times is shown in Fig. 5. Initially, the density of the epoxy resin increased marginally and began to decrease after about 36 h. This can be explained as follows: at the beginning of ageing, the high water absorption led to a rapid increase in mass, but the change in volume of the resin lagged behind the change in mass; therefore, water absorption in the initial 36 h did not result in a considerable volume change. Thereafter, the resin began to expand in volume with the gradual absorption and accumulation of water, thereby exhibiting an initial increase and a subsequent decrease in the density. After 456 h, the density of the epoxy resins essentially stabilised, approaching a saturation state of water absorption and no further increase in volume was observed.

3.1.3 Hardness

The variation in hardness of the epoxy resin with ageing time is shown in Fig. 6. The variation in hardness of the epoxy resins followed a similar trend in the two ageing modes. The hardness gradually decreased over time: the rate of decrease was initially rapid and subsequently reduced. The hardness level fluctuated around 843 HLD in later stages of ageing. During ageing tests, the hardness can indicate the loss of resin properties or the degree of damage. It is worth noting that the different ageing methods affect the hardness of resin at an essentially identical rate. The test depth of the Richter hardness is only about 10 µm and mainly determined by the surface property of the resin. Moreover, water penetrates inward from the outside, with water molecules getting into the outer resin and weakening the intermolecular force, thereby showing a decrease in hardness[25].

3.1.4 Infrared spectral analysis

The infrared spectra of the epoxy resins at different ageing times are shown in Fig. 7. The absorption peaks at 2948 cm^− 1 and 2862 cm^− 1 reflect the stretching vibrations of Alkyl units and C-H, respectively; the peak at 1729 cm^− 1 corresponds to the stretching vibration of C = O; peaks at 1610 cm^− 1 and 1512 cm^− 1 indicate aromatic structures; the peaks at 1450 cm^− 1 and 1380 cm^− 1 correspond to the bending vibrations of -CH₃ and C-H, respectively; the peak at 1180 cm^− 1 corresponds to the stretching vibration of C-O; and the peak at 829 cm^− 1 is the out-of-plane bending vibration of Ar-H.

The positions and relative intensities of the major absorption peaks in the infrared spectra of the epoxy resin castings before and after ageing were almost identical. This indicates that no significant bond breakage or bond formation occurred during the process and the two ageing modes did not impact the chemical structure of the resin. The absorption peaks at 1729 cm^− 1 and 1180 cm^− 1, attributed to the stretching vibrations of the carbonyl group and ether bond respectively, indicate the presence of ester groups. The hydrolysis of the ester bond can occur in a humid environment. However, the corresponding changes in the intensity of the absorption peaks in Fig. 7 at these two positions before and after ageing did not indicate the occurrence of the reaction. The structure of the benzene ring and cross-linked network increased the steric hindrance of the ester bond and hindered the hydrolysis. Although water permeation can lead to degradation of epoxy resin, hydrolysis was not found in this study. This is because the resin degradation is result of the comprehensive influence of epoxy chemical composition[26], temperature[16] and pH[14].

3.1.5 Thermogravimetric analysis

The thermogravimetric analysis curves of the epoxy resins before and after ageing are shown in Fig. 8. The initial decomposition temperature and the temperature at which the rate of weight loss is maximum are shown in Table 2. The weight loss curves of epoxy resins with different ageing durations in both ageing modes are essentially identical. Significant weight loss did not occur until the temperature reached 200°C: the weight loss was around a mere 1%, which was probably due to the removal of the absorbed moisture. Once the temperature reached 300°C, the weight of the sample began to decrease rapidly, indicating the breaking of chemical bonds and pyrolysis of the resins. Under both the ageing modes, the initial decomposition temperatures of the resins with various ageing times were between 340 ~ 342°C, and the temperature at which maximum weight loss occurred was approximately 378°C. The two ageing processes hardly affected the thermogravimetric properties of the epoxy resins as the absorbed water did not change the chemical network structure of the epoxy resin system. The absorbed water within the resins was bonded to the epoxy resin molecules through van der Waals force and hydrogen bonds, which had negligible effect on the thermal decomposition properties of the thermosetting epoxy resins investigated in this study [27, 28].

Table 2

Initial decomposition temperature and temperature at which the rate of weight loss of epoxy resins is maximum
Ageing mode	Ageing time	0 h	576h	1344 h	2160 h
Hygrothermal ageing	Initial decomposition temperature/°C	341.26	340.78	341.82	340.53
Hygrothermal ageing	Temperature at which the rate of weight loss is maximum/°C	378.13	377.73	378.88	378.59
Salt mist ageing	Initial decomposition temperature/°C	340.53	341.83	342.23	341.96
Salt mist ageing	Temperature at which the rate of weight loss is maximum /°C	378.59	378.31	377.22	378.79

3.1.6 SEM analysis

SEM images of the epoxy resin surface before and after ageing are shown in Fig. 9. The uneven surface of the microstructure of epoxy resins was probably caused by the low degree of surface finish on the inner wall of the mould and the shrunk volume of the cured resin. Comparison of the surface morphology of the epoxy resins before and after different ageing times indicated that hygrothermal and salt mist ageing did not significantly affect the microstructure of the epoxy resins.

3.2 Ageing properties of epoxy pultruded composites

3.2.1 Flexural strength

The three-point flexural strength of the epoxy pultruded composites at different ageing times are shown in Fig. 10. The flexural strengths of the composites in both hygrothermal ageing and salt mist ageing follow a similar trend. The initial flexural strength of the composites was 803 MPa; at first, it decreased with an increase in ageing time and eventually stabilized to approximately 760 MPa, with about 5.4% decrease. This implies that the two ageing modes had negligible effect on the bending properties of the composites. The reduction in the flexural strength was primarily due to the swelling of the resin on the material surface, the decreased strength of intermolecular forces, and the weakening of the matrix-fibre interface caused by water absorption[29]. Hygrothermal ageing and salt mist ageing had minimal effect on the resin matrix: water absorbed by the resin did not break the chemical bonds of the resin molecules. Glass and carbon fibre, the reinforcing materials of the composites, act as barriers against water penetration to a certain extent. Therefore, water hardly entered the inner layers of the composites. Hence, the strength of the composites did not exhibit a continuous decrease. In addition, the outermost layer of the composites was reinforced by glass fibre, which is an insulating material. Consequently, no electrochemical corrosion occurred, and salt mist ageing did not accelerate the decline in the flexural strength.

3.2.2 Impact Strength

The impact strengths of the epoxy pultruded composites at different ageing times are shown in Fig. 11. The variation in impact strength was largely similar to that of flexural strength, but the rate and magnitude of decrease in impact strength were relatively large. That is, the impact strength of the composites exhibits a substantially higher sensitivity to ageing. The impact strength of the composite prior to ageing was 383 MPa, and it stabilised to approximately 310 MPa in later stages of ageing, displaying a 19% decrease. Because the outer layer of the epoxy pultruded composite was a high-strength glass fibre fabric belt, which was classified as two-dimensional reinforcement and absorbed most of the impact energy during the impact process. The presence of island-type toughening agent may also increase the toughness of composites moisture environment[30]. Ageing primarily affected the outer layer structure of the composites, weakened the bonding between the epoxy resin and the outer fibre, and substantially reduced the impact strength[31].

3.2.3 SEM analysis

Figure 12 shows SEM images (at 500 × magnification) of the surface morphology of the epoxy pultruded composites at different ageing times. The surface microstructure of the composite materials mostly remained unchanged before and after hygrothermal and salt mist ageing. Moreover, no noticeable damage or flaking of the epoxy resins and fibres was observed. No salt particle deposition was observed on the surface of the materials after salt mist ageing. Furthermore, salt mist ageing showed no corrosive effect on the resin and fibres.

Figure 13 shows SEM images (at 20k × magnification) of the resin-fibre interface in epoxy pultruded composites at different ageing times. Although the fibre and resin did not change before and after ageing, micro-cracks appeared at the interface. Before ageing, resin and fibre were well bonded at the interface although the bonding was not very dense. Some micro-pores with a diameter of approximately 0.2 µm existed at the interface. Hence, the interface between the fibre on the outer surface of the composite and the resin matrix was a weak point in the material. The differences in thermal shrinkage rates of the fibre and the resin may result in a thermal stress at the interface, causing a substantial shrinkage of the outer layer, which affected the moisture diffusion[3]. The uneven resin content on the surface of composites may also promote the generation of cracks[32]. The SEM images after 240 h of ageing revealed that micro-cracks began to appear at the interface as the ageing time increased and extended along the axial direction of the fibre. After 3120 h, fractures developed at the edges of the interfacial cracks and part of the resin broke off. Water entered into the composite interface through the micro-pores created by shrinkage during the curing process. When the amount of water absorbed reached a certain threshold, the resin matrix began to expand and generated stress at the interface. As the water weakened the bonding strength at the interface, cracks formed between the fibre and the matrix and continued to expand along the direction of the interfacial stress.

The effects of hygrothermal ageing and salt mist ageing on the properties of epoxy/anhydride resins and their carbon fibre/glass fibre reinforced epoxy pultruded composites were comparatively investigated through artificially accelerated ageing experiments. The results showed that the two ageing modes had similar effects on the properties of the epoxy resins and their epoxy pultruded composites in terms of the manner and degree of impact. The two ageing modes did not cause significant changes to the chemical structure of the epoxy resins, and the ageing process mainly involved physical moisture adsorption. In the early ageing stage, the moisture absorption rate of salt mist ageing was slightly higher than that of hygrothermal ageing, and in the later stage, the moisture absorption rates gradually declined. After ageing for 2160 h, the moisture saturation rate remained at approximately 1.1% in both modes and the depth of moisture penetration across the thickness of the epoxy resin was approximately 0.27 mm. Both ageing modes negligibly affected the thermal decomposition properties and microstructure of the epoxy resins. Hygrothermal ageing and salt mist ageing affected the mechanical properties of epoxy resin composites. The flexural strength and impact strength decreased rapidly in the early ageing stage and stabilised at the later stage. After ageing for 5216 h, the flexural strength and impact strength of the composites decreased by 5.4% and 19%, respectively, due to moisture penetrating the interface of the composites, thus causing micro-cracks between the fibre and the resin.

The following statements should be included under the heading "Statements and Declarations" for inclusion in the published paper. Please note that submissions that do not include relevant declarations will be returned as incomplete.

Competing Interests: Authors are required to disclose financial or non-financial interests that are directly or indirectly related to the work submitted for publication. Please refer to “Competing Interests and Funding” below for more information on how to complete this section.

Funding:

This research was partly supported by National key research and development program of China (2021YFB3702700).

Author contributions

Kun Qiao, Shengzong Ci and Chengrui Di: designed experiments, conducted the experiments, analyzed the data and wrote the papers; Bo zhu, Junwei Yu and Baoming Wang: advised, supervised the experiments. All authors reviewed the manuscript.

Rocha IBCM, Raijmaekers S, Nijssen RPL, van der Meer FP, Sluys LJ. Hygrothermal ageing behaviour of a glass/epoxy composite used in wind turbine blades. Compos Struct. 2017;174:110-22. https://doi.org/10.1016/j.compstruct.2017.04.028
Simar A, Gigliotti M, Grandidier JC, Ammar-Khodja I. Evidence of thermo-oxidation phenomena occurring during hygrothermal aging of thermosetting resins for RTM composite applications. Composites Part A: Applied Science and Manufacturing. 2014;66:175-82. https://doi.org/10.1016/j.compositesa.2014.07.007
Barjasteh E, Nutt SR. Moisture absorption of unidirectional hybrid composites. Composites Part A: Applied Science and Manufacturing. 2012;43(1):158-64. https://doi.org/10.1016/j.compositesa.2011.10.003
Rezgani L, Madani K, Feaugas X, Touzain S, Cohendoz S, Valette J. Influence of water ingress onto the crack propagation rate in a AA2024-T3 plate repaired by a carbon/epoxy patch. Aerospace Science and Technology. 2016;55:359-65. https://doi.org/10.1016/j.ast.2016.06.010
Zhang Y, Ma J, Wu C, Han X, Zhang W, Zhang W. Effects of moisture ingress on the mesoscale mechanical properties of epoxy adhesives under elevated temperature. Polymer Testing. 2021;94. https://doi.org/10.1016/j.polymertesting.2020.107049
Chowdhury IR, O'Dowd NP, Comer AJ. Experimental study of hygrothermal ageing effects on failure modes of non-crimp basalt fibre-reinforced epoxy composite. Compos Struct. 2021;275. https://doi.org/10.1016/j.compstruct.2021.114415
Robert C, Pecur T, Maguire JM, Lafferty AD, McCarthy ED, Ó Brádaigh CM. A novel powder-epoxy towpregging line for wind and tidal turbine blades. Composites Part B: Engineering. 2020;203. https://doi.org/10.1016/j.compositesb.2020.108443
Grammatikos SA, Evernden M, Mitchels J, Zafari B, Mottram JT, Papanicolaou GC. On the response to hygrothermal aging of pultruded FRPs used in the civil engineering sector. Materials & Design. 2016;96:283-95. https://doi.org/10.1016/j.matdes.2016.02.026
Guo R, Xian G, Li C, Hong B, Huang X, Xin M, et al. Water uptake and interfacial shear strength of carbon/glass fiber hybrid composite rods under hygrothermal environments: effects of hybrid modes. Polym Degrad Stabil. 2021;193. https://doi.org/10.1016/j.polymdegradstab.2021.109723
Rudawska A. The Effect of the Salt Water Aging on the Mechanical Properties of Epoxy Adhesives Compounds. Polymers (Basel). 2020;12(4). https://doi.org/10.3390/polym12040843
Quino G, Tagarielli VL, Petrinic N. Effects of water absorption on the mechanical properties of GFRPs. Compos Sci Technol. 2020;199. https://doi.org/10.1016/j.compscitech.2020.108316
Earl JS, Shenoi RA. Hygrothermal ageing effects on FRP laminate and structural foam materials. Composites Part A: Applied Science and Manufacturing. 2004;35(11):1237-47. https://doi.org/10.1016/j.compositesa.2004.04.007
Clancy TC, Frankland SJV, Hinkley JA, Gates TS. Molecular modeling for calculation of mechanical properties of epoxies with moisture ingress. Polymer. 2009;50(12):2736-42. https://doi.org/10.1016/j.polymer.2009.04.021
Capiel G, Uicich J, Arrosio F, Fasce D, Morán J, Montemartini PE. pH Effect on epoxy-anhydride water aging. Polym Degrad Stabil. 2021;193. https://doi.org/10.1016/j.polymdegradstab.2021.109747
Wang M, Xu X, Ji J, Yang Y, Shen J, Ye M. The hygrothermal aging process and mechanism of the novolac epoxy resin. Composites Part B: Engineering. 2016;107:1-8. https://doi.org/10.1016/j.compositesb.2016.09.067
Guermazi N, Ben Tarjem A, Ksouri I, Ayedi HF. On the durability of FRP composites for aircraft structures in hygrothermal conditioning. Composites Part B: Engineering. 2016;85:294-304. https://doi.org/10.1016/j.compositesb.2015.09.035
Wang Y, Zeng Z, Gao M, Huang Z. Hygrothermal aging characteristics of silicone-modified aging-resistant epoxy resin insulating material. Polymers (Basel). 2021;13(13). https://doi.org/10.3390/polym13132145
Grammatikos SA, Ball RJ, Evernden M, Jones RG. Impedance spectroscopy as a tool for moisture uptake monitoring in construction composites during service. Composites Part A: Applied Science and Manufacturing. 2018;105:108-17. https://doi.org/10.1016/j.compositesa.2017.11.006
El Yagoubi J, Lubineau G, Saghir S, Verdu J, Askari A. Thermomechanical and hygroelastic properties of an epoxy system under humid and cold-warm cycling conditions. Polym Degrad Stabil. 2014;99:146-55. https://doi.org/10.1016/j.polymdegradstab.2013.11.011
Wan YZ, Wang YL, Huang Y, He BM, Han KY. Hygrothermal aging behaviour of VARTMed three-dimensional braided carbon-epoxy composites under external stresses. Composites Part A: Applied Science and Manufacturing. 2005;36(8):1102-9. https://doi.org/10.1016/j.compositesa.2005.01.003
Park SY, Choi WJ, Choi HS. The effects of void contents on the long-term hygrothermal behaviors of glass/epoxy and GLARE laminates. Compos Struct. 2010;92(1):18-24. https://doi.org/10.1016/j.compstruct.2009.06.006
Boukhoulda BF, Adda-Bedia E, Madani K. The effect of fiber orientation angle in composite materials on moisture absorption and material degradation after hygrothermal ageing. Compos Struct. 2006;74(4):406-18. https://doi.org/10.1016/j.compstruct.2005.04.032
Guo F-L, Huang P, Li Y-Q, Hu N, Fu S-Y. Multiscale modeling of mechanical behaviors of carbon fiber reinforced epoxy composites subjected to hygrothermal aging. Compos Struct. 2021;256. https://doi.org/10.1016/j.compstruct.2020.113098
Qiao K, Zhu A, Wang B, Di C, Yu J, Zhu B. Characteristics of Heat Resistant Aluminum Alloy Composite Core Conductor Used in overhead Power Transmission Lines. Materials (Basel). 2020;13(7). https://doi.org/10.3390/ma13071592
Cabanelas J. Water absorption in polyaminosiloxane-epoxy thermosetting polymers. Journal of Materials Processing Technology. 2003;143-144:311-5. https://doi.org/10.1016/S0924-0136(03)00480-1
Zinck P, Gerard J. Thermo-hydrolytic resistance of polyepoxide–glass fibres interfaces by the microbond test. Compos Sci Technol. 2008;68(9):2028-33. https://doi.org/10.1016/j.compscitech.2008.02.025
Prolongo SG, Gude MR, Ureña A. Water uptake of epoxy composites reinforced with carbon nanofillers. Composites Part A: Applied Science and Manufacturing. 2012;43(12):2169-75. https://doi.org/10.1016/j.compositesa.2012.07.014
Popineau S, Rondeau-Mouro C, Sulpice-Gaillet C, Shanahan MER. Free/bound water absorption in an epoxy adhesive. Polymer. 2005;46(24):10733-40. https://doi.org/10.1016/j.polymer.2005.09.008
Niu Y-F, Yan Y, Yao J-W. Hygrothermal aging mechanism of carbon fiber/epoxy resin composites based on quantitative characterization of interface structure. Polymer Testing. 2021;94. https://doi.org/10.1016/j.polymertesting.2020.107019
Zhong Y, Joshi SC. Environmental durability of glass fiber epoxy composites filled with core–shell polymer particles. Materials & Design. 2016;92:866-79. https://doi.org/10.1016/j.matdes.2015.12.124
Mamalis D, Floreani C, Ó Brádaigh CM. Influence of hygrothermal ageing on the mechanical properties of unidirectional carbon fibre reinforced powder epoxy composites. Composites Part B: Engineering. 2021;225. https://doi.org/10.1016/j.compositesb.2021.109281
Liotier P-J, Vautrin A, Beraud J-M. Microcracking of composites reinforced by stitched multiaxials subjected to cyclical hygrothermal loadings. Composites Part A: Applied Science and Manufacturing. 2011;42(4):425-37. https://doi.org/10.1016/j.compositesa.2011.01.003

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Effects of hygrothermal and salt mist ageing on the properties of epoxy resins and their composites

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental Procedures

2.1. Materials

2.2 Sample preparation

2.2.1 Preparation of epoxy resin castings

2.2.2 Preparation of carbon fibre/glass fibre hybrid reinforced epoxy pultruded composites

2.3 Experimental methods

2.3.1 Hygrothermal ageing

2.3.2 Salt mist ageing

2.3.3 Ageing time

2.4 Characterisation methods

3 Results And Discussion

3.1 Ageing properties of epoxy resin castings

3.1.1 Moisture absorption

3.1.2 Density

3.1.3 Hardness

3.1.4 Infrared spectral analysis

3.1.5 Thermogravimetric analysis

3.1.6 SEM analysis

3.2 Ageing properties of epoxy pultruded composites

3.2.1 Flexural strength

3.2.2 Impact Strength

3.2.3 SEM analysis

4. Conclusions

Declarations

Funding:

Author contributions

References

Additional Declarations

Status:

Version 1