Strength Retention Research Articles

A novel method of reclaiming high-value carbon fiber from waste epoxy composite via molten salt thermal treatment

Epoxy resin limits the recycling of high-value carbon fibers from waste epoxy composites: its inferior thermal conductivity requires the excessive pulverization of the polymers, reducing fibers length; its robust cross-linked structure hinders its removal, leading to fiber contamination. Here, we proposed a novel method by using molten salts as an effective medium to enhance heat transfer and thermal reaction. The length and structural integrity of fibers were preserved by minimizing the extent of pulverization and reducing the erosive impact of resin degradation products, respectively. At 375 °C, the resin removal ratio and fiber strength retention both exceeded 99%, with a temperature reduction of at least 100 °C. Molten salts exerted differential inert and active effects on fibers and resin. Fibers could retain 97% of strength retention within salts at 400 °C for 2 h. Conversely, molten salts significantly facilitated the disruption of the resin matrix’s cross-linked structure by catalyzing the cleavage of C-N bonds. The degradation products exhibited a lightweight tendency and could be easily separated from the fiber surface in the fluid environment provided by molten salts, thus protecting the fiber surface against oxidative erosion caused by phenols.

Fluorinated natural rubber with enhanced strength and excellent resistance to ozone, organic solvent, and acid and alkali via in situ reactive melt extrusion

Natural rubber (NR), as a green and renewable industrial raw material, is applied in many fields. However, the relatively weak resistance originated from its unsaturated backbone structure restricts the further application in some harsh conditions. To incorporate the excellent resistance feature of the fluorinated components into NR, fluorinated natural rubber (FNR) was prepared with dodecafluoroheptyl methacrylate (DFHMA) via in situ melt extrusion reaction. The results indicated that fluorinated reaction of NR mainly happened at the α-H of double bond in backbone chain and that styrene could promote fluorination and increase the size of fluorinated side chain. The vulcanized FNR (VFNR) exhibited wonderful mechanical performance, remarkable hydrophobicity, and excellent resistance to ozone, organic solvent, acid and alkali. The water contact angles of VFNR increased from 89 ° to 104 °and the ozone aging cracking time of VFNR increased by one time longer than that of VNR. The swelling degree of VFNR in the full synthetic engine oil is only two-thirds that of VNR, and the retention of tensile strength after immersion in HCl, H2SO4, and NaOH solution was elevated by 13 %, 11 %, and 5 % compared to those of VNR, respectively. This work presents a simple and eco-friendly method to prepare the fluorinated natural rubber facilitating the industrial fabrication of green and high-performance NR via melt extrusion.

Effect of fly ash and curing temperature on the properties of magnesium phosphate repair mortar

This article is aimed at discussing the combined effect of mineral admixture and servicing temperature, especially in cold environment, on the properties of magnesium phosphate repair mortar (MPM). The influence mechanism of fly ash content on the microstructure and performance of MPM were firstly investigated, and then the evolution rules in properties of fly ash modified MPM cured at − 20 °C, 0 °C, 20 °C and 40 °C were further revealed. The results show that the incorporation of fly ash has no significant effect on the setting time and fluidity of MPM. When MPM is modified with 10 wt% and 15 wt% fly ash, its mechanical properties, adhesive strength, water resistance, and volume stability are effectively improved. Fly ash reduces the crystallinity and continuity of struvite enriched in hardened MPM, and its particles are embedded among struvite and unreacted MgO. The compressive strength of MPM-10 cured for various ages increases with the elevating of curing temperature, while the flexural strength, interfacial bonding strength, strength retention and linear shrinkage exhibits the opposite laws. When cured at 0 °C and − 20 °C, MPM-10 still has good early strength, water resistance and interfacial bonding properties, which indicates that MPM-10 provides with an ability of emergency repair of cracked components served in cold environments.

Computationally guided alloy design and microstructure-property relationships for non-equiatomic Ti–Zr–Nb–Ta–V–Cr alloys with tensile ductility made by laser powder bed fusion

Single-phase body-centered cubic refractory complex concentrated alloys (RCCAs), exhibit strength retention at temperatures above the melting points of conventional Ni-based superalloys. However, their lack of room temperature tensile ductility leads to cracks during processing and/or premature failure under mechanical loading when fabricated by laser-based metals additive manufacturing (AM). We present an alloy design framework for tensile ductility in non-equimolar RCCAs amenable to AM processing within the Ti–V–Cr–Nb–Zr–Ta system. First, density functional theory (DFT) and machine learning informed screening of alloy compositions were used to down-select ∼106 alloys with potential for tensile ductility. Next, Scheil solidification modeling was used to eliminate compositions most at risk for micro-segregation and solidification cracking based on the estimated freezing range of each alloy. This led to the design of two new, representative alloys: Ti0.4Zr0.4Nb0.1Ta0.1 and Ti0.486V0.375Ta0.028Cr0.111. These alloys were evaluated for rapid solidification defect formation using in-situ synchrotron melt pool imaging, fabricated via laser powder bed fusion (L-PBF) AM, and then characterized for processing defects, microstructure, and mechanical properties. Overall, both alloys achieved tensile yield strengths >800 MPa and failure strains >5 %. However, the occurrence of un-melted powders of high melting point elements likely resulted in premature failure during tensile straining. Considerations about mitigating this defect source are discussed and the role of local micro-segregation on ductility are elucidated. Overall, these results highlight the success of our framework, and show potential for laser-based AM-RCCAs with tensile ductility.

Development of large-size dissimilar stainless steel/α-Ti alloy joints by diffusion bonding using vacuum hot press: Interface microstructure and tensile response in the temperature range of 77–773 K

In the present study, dissimilar metal joints of SS321 and Ti–5Al-2.5Sn (α-Ti alloy) are produced by diffusion bonding at temperatures of 850, 900, and 950 °C under 10 MPa pressure for 30 min duration using a vacuum hot press (VHP). The interface of the joints was characterized through scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscattered diffraction analysis for examining microstructure, morphology, and microchemistry across the interface. The effect of change in the heating process during diffusion bonding on the growth kinetics of interface layers was investigated. The interface of the joints comprised of intermetallic phases of σ phase, χ phase, (Fe,Cr)2Ti, FeTi and β-Ti. The joint produced at 900 °C has exhibited a maximum tensile strength of 315 MPa, 253 MPa, and 208 MPa at the test temperatures of −196 °C (77 K), room temperature (300 K), and 500 °C (773 K), respectively. Reduction in joint strength was noticed at test temperatures of RT and −196 °C for the samples bonded at a higher temperature of 950 °C due to the increased widths of the intermetallic phases at the interface. The effect of the bonding temperature on the tensile strength of the joints at an elevated test temperature of 500 °C was found to be negligible; however, the joints displayed good retention of strength along with substantial strain hardening followed by ductility at 500 °C. Fracture surfaces of RT and −196 °C tested samples showed the mixed mode of featureless smooth and cleavage fracture, whereas the 500 °C tested sample displayed planar interface failure. The zone of failure of the joints was noted to be around the interphase layer made of (Fe,Cr)2Ti + FeTi intermetallics.

Micro- and macro- mechanical properties of an Al2O3/Al2O3 ceramic matrix composite after thermal aging at 1400 °C

The evolution mechanism of mechanical properties at elevated temperature is particularly crucial to the oxide/oxide composites. In this work, an Al2O3/Al2O3 ceramic matrix composite was prepared by laminating with high solid content slurry. The microstructure, micro- and macro- mechanical properties of the composites before and after thermal aging at 1400 °C were examined. The density and porosity of the original composite were ∼2.60 g/cm3 and ∼27.2 %, respectively. The sintering phenomenon of matrix in the composite after thermal aging was clearly visible, resulting in the matrix modulus increased by 83.5 % and the interfacial shear strength increased by 154.9 % compared with those of the original composite. The fundamental mechanics theory of composites stated that the significant increase of interfacial shear strength was the main reason that the flexural strength retention ratio of the composite decreased to ∼55 % after thermal aging.

Impact damage resistance and tolerance of alumina-based oxide/oxide ceramic matrix composite upon one sided thermal shock and hold

In this study, ceramic matrix composite specimens constituting Nextel™720 fibers and alumina matrix were subjected to one-sided thermal shock and subsequent 30-min hold at temperatures of 1200℃, 1350℃ and 1500℃. The plates were then subjected to low velocity impact at 5 J impact energy, followed by edgewise compression with digital image correlation. No noticeable change in mass, roughness and specimen dimensions were observed after the thermal shock and hold event at any of the temperatures for any of the specimens. External and internal damage resulting from the impact event also showed no dependence on the thermal shock temperature. The percentage compressive strength retention after low velocity impact ranged from 61 % to 68 % for all cases considered, again with no trends observed based on shock temperature. However, the compressive modulus for the impacted panels that were exposed to high temperature were higher than the pristine (non-thermal shocked) impacted panels.

Durability of externally strengthened concrete prisms with CFRP laminates and galvanized steel mesh attached with epoxy adhesives and mortar

The long-term bond degradation and strength retention of flexural bond prisms strengthened with carbon fiber-reinforced polymer (CFRP) composite and galvanized steel mesh (GSM) systems, bonded to concrete using epoxy adhesives and cement-based mortar under aggressive conditioning regimes are compared in this paper. Notched prisms strengthened using low-cord density steel mesh (LSM) with epoxy (SME-strengthened) and cement mortar (SMM-strengthened), and CFRP-epoxy systems were weathered under saline water and direct sunlight for a period of 28 and 540 days. The results of the study were analyzed based on experimentally obtained ultimate load (Pu) values and empirically calculated average bond shear stress (τavg) and prism strength retention (Rp) values. The bond strength degraded by 39 and 34 % in CFRP strengthened, 2.9 and 33 % in SME strengthened, and 2.8 and 10.8 % in SMM-strengthened specimens following the 540-day exposure to saline water and direct sunlight, respectively. The average prism retention ratio was calculated to be 0.61 and 0.66 for CFRP-strengthened, 0.97 and 0.67 for SME-strengthened, and 0.97 and 0.89 for SMM-strengthened specimens after 540 days of saline water and direct sunlight exposure. Flexural prism environment strength reduction factors (CE) were proposed as 0.60, 0.95, and 0.95 for CFRP, SME, and SMM-strengthened specimens under saline water exposures and 0.65, 0.65, and 0.85 for CFRP, SME, and SMM strengthened specimens under direct sunlight exposures. Saline water exposure was observed to be most critical to all strengthening systems. Although CFRP-strengthened specimens showed minimum degradation in load-carrying capacity under both conditioning regimes, they showed maximum bond strength reduction in contrast to SMM-strengthened specimens. It was observed that the choice of bonding agent significantly influenced the extent of bond strength degradation under extreme exposure regimes, like those that prevail in the UAE and the Persian Gulf.

Oxidation behavior of sol-derived C/Mullite composites in air

Thanks to the reinforcing and toughening of carbon fiber, carbon fiber reinforced mullite (C/Mullite) composites exhibit favorable application potential as thermal structural materials. To further reveal the failure mechanism of the C/Mullite composites in service environment, the oxidation resistance and failure behavior of the composites were systematically investigated in this study. It was found that the oxidation mechanism of the composites inclined to diffusion control at 1300 °C∼1500 °C, the cracks and pores of the composites provided diffusion channels for oxygen to oxidize the composites, the oxidation degree of carbon fibers and interfacial coating after oxidation was responsible for the weight loss and performance degradation of the composites. Additionally, the oxidation resistance of C/Mullite composites can be obviously enhanced by using the SiO2-rich (the Al/Si atomic ratio was 1/2) Al2O3–SiO2 sol to densify at the later stage of fabrication, strength retention and modulus retention of the composites were increased by 28 % and 40 % after oxidation at 1500 °C in air, respectively.

Water absorption and property evolution of epoxy resin under hygrothermal environment

Changes in structure and properties of resin matrix caused by water absorption is one of the key factors affecting the long-term durability of fiber reinforced polymer composites used in civil engineering. In the present study, the water diffusion and structural change in an epoxy resin were investigated experimentally through immersion in deionized water at 40, 60 and 80 °C for 135 days. Water absorption, thermal, mechanical and microstructure analysis tests were conducted to evaluate the long-term property evolution. It was found that the water absorption of epoxy resin followed a two-stage model, including an initial Fick's diffusion response and a subsequent relaxation response. Long-term hygrothermal exposure brought about the structural change of epoxy resin, which led to the significant degradation up to 8%–30% in the mechanical properties and 21% in glass transition temperature, respectively. The resin plasticization and hydrolysis was the key factors for the degradation of thermal and mechanical properties. It was proved that the plasticization effect was reversible with the remove of bonding water after the drying. Based on the Arrhenius equation, the long-term life of flexural strength in two service environments were predicted to provide the application guideline. The significant degradation of flexural strength was occurred at the initial exposure of 2000 days and then reached to the stable strength retention of 69.6%.

Ultra strong, tough and extreme environments resistant PBO papers with a nacre-like structure constructed by synergistic electrostatic interaction and interlayer entanglement

In extreme environments, it is difficult to balance the strength and toughness of ultra-thin film materials. To address this problem, we propose a promising strategy to build ultra strong, tough and extreme environments resistant Poly(p-phenylene-2,6-benzobisoxazole) (PBO) papers with a nacre-like structure constructed by synergistic electrostatic interaction and interlayer entanglement through the sol–gel-film method and hot press orientation. Highly interconnected PBO nanofibres （PNFs） with positive charges are tightly wound around the anisotropic graphene oxide (GO) nanosheets with negative charges through strong electrostatic interaction, forming a nacre like microstructure. The addition of Fe (Ⅲ) can form a coordination bond with the amino group on PNFs. Chemical crosslinking and hydrogen bonding synergize with interlayer entanglement effect among different PNFs，which can effectively dissipate interlayer energy and alleviate the conflict between strength and toughness. The resultant tensile strength and toughness are as high as 338.3 MPa and 16.04 MJ/m3，which are 197.7 % and 425.4 % of those of the intrinsic PBO paper, respectively. Additionally, after 5000 folding-unfolding cycles, the tensile strength retention and toughness retention of the PBO/GO/Fe (PGFe) paper were still 85.4 % and 71.9 %, respectively. Moreover, the paper exhibits excellent tolerance to extreme temperature environments and showed extremely strong chemical stability.

Accelerated aging tests of large-diameter GFRP bars in alkaline environment

Fiber reinforced polymer (FRP) bars have become increasingly popular, while the studies on durability of FRP bars are primarily on small-diameter FRP bars. This study investigated the tensile strength retention in glass FRP (GFRP) bars of different diameters (13 mm and 25 mm) after immersion in an alkaline solution (pH=12.6) at various temperatures (20 °C, 40 °C and 60 °C) for 1, 2, 3, and 6 months. The results reveal that the degradation of GFRP bars was slow at 20 °C, accelerated but not pronounced at 40 °C and considerable at 60 °C. Particularly, the 13 mm diameter GFRP bars exhibited a more significant reduction in tensile strength, with a decrease of 20.12 % after 6 months, while the 25 mm diameter bars only decreased by 13.23 %. Results reveal that, importantly, degradation of GFRP bars is primarily attributed to the diffusion of the moisture and alkalis, which disrupts the bond between the fibers and the matrix, causing interface damage. Finally, based on the Arrhenius theory, it is predicted that the tensile strength retention of 13 mm and 25 mm diameter GFRP bars will be 66.4 % and 79.8 %, respectively, after 50 years of exposure at an average annual temperature of 35 °C. The important finding that the small-diameter FRP bars are more vulnerable to the alkaline exposure than larger diameter bars suggests that the current studies on durability of FRP bars are conservative to be referred in practice.

Utilization of agro waste activated carbons as carbon black replacement in electron beam irradiated styrene butadiene rubber composites

Purpose This study aims to prepare activated carbon (AC) and activated biochar (BC) from sugarcane bagasse (SCB) can be used as carbon black (CB) replacement for styrene butadiene rubber (SBR) composites cured by electron beam (EB) radiation. Design/methodology/approach This study is carried out to investigate the effect of partial replacement of CB (as traditional filler) by AC or BC prepared from low-cost agricultural wastes (SCB) to improve the properties of SBR rubber cured by EB radiation (doses from 25 to 150 kGy). Findings The results indicated that the addition of AC or BC leads to improve the physical and mechanical properties of SBR with increasing irradiation dose [especially at concentration of 10 parts per hundred part of rubber (phr) from BC]. Also in this study, this paper examines how exposure of SBR rubber composites to ultraviolet (UV) radiation changes the mechanical properties for these composites, to do that, the specimens were examined before and after they were exposed to UV radiation for 300 h. The results showed that, the irradiated SBR composites, UV exposure, exhibit better retention in mechanical properties as compared with unirradiated ones, and the samples loaded with CB hybrid with ACs had an increased value of tensile strength (TS) retention as compared with blank sample. Originality/value The importance of this study is that, the production of AC from SCB offers a huge opportunity to overcome the problem of the disposal of SCB.

Development and characterization of anti-cracking epoxy asphalt for steel deck pavement

Despite being commonly utilized in long-span steel deck pavement, epoxy asphalt continues to encounter certain obstacles, including excessive strength and insufficient resistance to cracking. This study proposed a novel approach to incorporating epoxy-terminated polyurethane prepolymers (ETPU) as a toughener to prepare an anti-cracking epoxy asphalt binder. The reaction process, viscosity-time behavior, tensile properties, and dynamic mechanical features of the ETPU-modified epoxy asphalt binder were comprehensively evaluated through a series of tests. Additionally, the fundamental pavement performance, fracture resistance, and fatigue resistance of ETPU-modified epoxy asphalt mixtures were thoroughly assessed. The addition of ETPU can significantly enhance the damping properties of epoxy asphalt, while maintaining its strength and construction retention time without any significant compromise. The formation of a chemical bond between epoxy-amine molecules and asphalt molecules significantly enhanced the compatibility between the epoxy resin phase and asphalt, thereby improving its damping properties. Both the fracture resistane and the fatigue resistance of ETPU-modified epoxy asphalt mixtures were found to be superior to that of commonly used epoxy asphalt mixtures in engineering. The modification mechanism was ultimately derived through the integration of infrared spectral analysis, thereby presenting an economically viable and highly efficient toughening pathway for epoxy asphalt. Therefore, this study indicated a wide-ranging potential for application in the realm of steel bridge deck pavement.

Bending behavior and damage evolution of GLARE laminate using in‐situ AE technology and FEM

AbstractGLARE laminate experiences multiple damage modes during bending failure, including fiber fracture, matrix cracking, interlayer delamination, and fracture of aluminum alloy. In most cases, two or more failure modes occur together, which makes the damage process complex and unpredictable. This paper proposes a combination of experimental testing and numerical simulation to investigate the influence of fiber lay‐up direction and center open‐hole on the bending failure behavior of GLARE laminate. Simultaneously, Acoustic Emission (AE) technology was used to monitor the bending process of GLARE laminates in real‐time, and a numerical simulation model for the three‐point bending of GLARE laminates was established. The experimental results showed that the bending strength of intact specimens decreased significantly with the increase of the fiber off‐axis angle, whereas the strength retention of open‐hole specimens increased significantly with the increase of the fiber off‐axis angle. Based on the K‐means++ clustering algorithm, the peak frequencies corresponding to different damage modes of GLARE laminates were identified as follows: aluminum alloy damage [1–70 kHz], matrix cracking [93–210 kHz], interlaminar delamination [211–304 kHz], and fiber breakage [304–516 kHz]. The simulation results agreed well with the experimental results, showing that the damage in intact specimens initiated at the laminate edges and propagated sequentially along the thickness direction, while the damage in open‐hole specimens initiated at the hole edges and then propagated towards the laminate edges.Highlights The present study investigated the effects of fiber lay‐up direction and central open‐hole on the bending performance and failure behavior of GLARE laminate. In‐situ monitoring of the GLARE laminate during three‐point bending was conducted using AE technology. A model for simulating the progressive damage of GLARE laminate was established and its accuracy was verified.

Effect of pattern fabrication methods on retentive strength in three‐unit implant‐supported frameworks: A comparative analysis

AbstractObjectiveGiven the significant role of retention in the long‐term success of implant‐supported prostheses, this study aimed to compare the retentive strength of three‐unit implant‐supported frameworks manufactured using the conventional, subtractive milling, and 3D printing methods.Materials and MethodsIn this in vitro study, two fixture analogs were placed in the mandibular right first premolar and first molar region of a Dentiform model, and two prefabricated abutments were secured in the fixture analogs. A total of 27 three‐unit frameworks were fabricated utilizing wax patterns prepared through conventional, milling, and 3D printing techniques (n = 9 per group). The frameworks were cemented with zinc oxide eugenol and subjected to thermocycling. The retentive strength of each specimen was evaluated through a pull‐out test conducted with a universal testing machine. The data were analysed using one‐way ANOVA and Tukey's post hoc test (p < 0.05).ResultsThe three groups were found to be significantly different (p = 0.01). While the 3D printing and milling groups were not significantly different (p = 0.99), they yielded significantly higher retentive strength compare to the conventional group (p = 0.02 for 3D printing and p = 0.03 for milling group).ConclusionThe utilization of 3D printing and milling technique for wax pattern preparation significantly increased the retention of the implant‐supported framework, with no statistically significant difference between the two methods.

Optimising compressive strength properties of seawater sea sand concrete-filled hybrid carbon-glass fibre-reinforced tubes: A study on the impact of layer sequencing

Utilising fibre-reinforced polymer (FRP) composites with seawater and sea sand concrete (SWSSC) in coastal regions tackles environmental concerns linked to traditional concrete and corrosion issues of conventional steel reinforcements. While previous studies have explored the mechanical properties of single-material FRP tubes, such as glass fibre-reinforced polymer (GFRP) and carbon fibre-reinforced polymer (CFRP), research on the durability of hybrid fibre tubes has been limited to a single stacking lay-up configuration. This study aims to investigate how layer sequencing affects the compressive strength properties of SWSSC-filled hybrid glass-carbon FRP (HFRP) tubes under seawater exposure. It explores two different fibre orientations, namely cross-ply and hoop. One approach which has been used in this study involves constructing tubes where 50 % of the inner tube thickness comprises CFRP layers and 50 % of the outer tube thickness comprises GFRP layers, while another approach alternates carbon and glass layers throughout the tube thickness. Laboratory accelerated ageing tests involved three temperatures (25°C, 40°C, and 60°C) and three conditioning durations (30, 90, and 150 days). Arrhenius predictive models were used to predict the tubes’ long-term residual compressive strength. The results indicate that the 50 %-50 % layer configuration outperforms the layer-by-layer arrangement in cross-ply tubes, with a service life strength retention of 63.9 % in the 50 %-50 % layer configuration compared to 48.8 % in the layer-by-layer configuration. However, no significant difference was observed between the two configurations in hoop tubes. This suggests that utilising CFRP as inner layers in cross-ply fibre-oriented tubes can potentially slow down damage progression from the harsh SWSSC environment toward the GFRP layers across the tube thickness. However, given that the compressive load acts perpendicular to the orientation of the fibres, the resin contributes more to the load-carrying capacity of the hoop-oriented fibres than cross-ply fibre tubes. This suggests that solely relying on this sequencing strategy may not yield highly effective results in this specific orientation. Implementing an alkaline-resistant coating on the inner surface of the tubes or augmenting the tube thickness are potential approaches to further delay damage progression, especially in hoop-oriented tubes.

Durability of concrete-embedded GFRP bars after 20 years of tidal zone exposure: Correlation with accelerated aging tests

The application of non-metallic glass fiber-reinforced polymer (GFRP) bars as embedded reinforcement in reinforced concrete (RC) has been of great interest among researchers and practicing engineers alike, owing to its properties such as high strength-to-weight ratio and corrosion resistance. This study investigated the long-term performance of ribbed (RB) and sand-coated (SC) GFRP bars embedded in concrete columns exposed to harsh seawater conditions for approximately 20 years. The bars extracted from the concrete elements were tested to evaluate strength retention based on ASTM standard transverse and interlaminar shear strength tests. After the long-term field exposure, the ribbed and sand-coated GFRP bars exhibited 82.5 % and 79.4 % transverse shear strength retention, and 84.4 % and 78.1 % interlaminar shear strength retention, respectively, which corresponds to approximately 5 months of exposure in the accelerated solution specified by ACI 440.3R-12 guide. Scanning electron microscopy analyses revealed the extent of damage in the fibers, the matrix, and their interface, which validated the degradation in the mechanical strength of the exposed GFRP bars. Finally, correlations between long-term and accelerated exposure test conditions were developed to predict transverse and interlaminar shear strength in the field based on laboratory conditioning investigations.

Enhanced mechanical strength and water resistance in waterborne polyurethanes through hydroxyl-functionalized MQ silicone resin modification

As an alternative to solvent-based polyurethane, waterborne polyurethane (WPU) uses water as dispersants and can significantly reduce VOC. However, dispersing polyurethanes with hydrophobic backbones in water requires hydrophilic groups, which undermine the water resistance. It remains a challenge to simultaneously improve water resistance and mechanical properties. Here we report a polyurethane with superior mechanical properties and water resistance through the introduction of an organic-inorganic hybrid material, MQ silicone resin. Hydroxyl functionalized MQ silicone resin increases chemical crosslinking and improves the microphase separation and hydrogen bonding strength of polyurethanes. When the MQ-OH content was 10.1 wt%, the tensile strength increased from 27 MPa to 37.3 MPa, and the toughness increased from 74.8 MJ/m3 to 97.4 MJ/m3. Si-O-Si backbones with low surface energy can migrate to the film surface, increasing the surface hydrophobicity. WPU films with MQ silicone resin exhibited remarkable tensile strength retention, with 84.7 % after 40 h hydrolysis in 80 °C water, while WPU retained only 24.6 %. MQ silicone resin offers a novel approach to enhance the hydrophobic properties of WPU without compromising the mechanical properties.

Enhancing radiation resistance of silicone rubber through the addition of polydopamine-modified cerium dioxide

With the widespread use of nuclear science and technology, slowing down the aging of polymers in a radiation environment has become a matter of great concern. In this work, cerium dioxide (CeO2) and CeO2 encapsulated with dopamine (PDA@CeO2) were selected as special fillers to prepare the silicone rubber (SR) composites, and their radiation resistance were investigated by comparing the mechanical properties and thermal performance before and after irradiation. The interfacial bridge formed by PDA results in a greater elongation at break for PDA@CeO2/SR5.0 (770.0 ± 33.6 %) than for CeO2/SR (686.0 ± 15.0 %). After irradiation with γ-rays, the retention of elongation at break of both CeO2/SR0.1 and PDA@CeO2/SR0.1 were larger than SR. Furthermore, PDA@CeO2/SR0.1 showed an impressive retention of 90.5 ± 2.7 % of the tensile strength retention after exposure to an absorbed dose of 200 kGy. The disparity in crosslink density prior to and following irradiation indicated that both CeO2 and PDA@CeO2 were efficacious in reducing radiation crosslinking within the SR. An electron paramagnetic resonance spectrometer and an ultraviolet lamp (UV-EPR) were used to observe in real time the free radical scavenging ability of CeO2 and PDA@CeO2 inside the SR. These results indicated that CeO2 and PDA@CeO2 was expected to prevent further chain reactions in silicone rubber by scavenging free radicals generated in SR, thus improving the radiation resistance of SR.