Hydrolysis Of Resin Research Articles

Hygrothermal aging mechanism of epoxy composites used for medium-frequency transformers

The integration of medium-frequency transformer design and the harsh service environment raise higher demands for the medium-frequency insulation performance of epoxy composites. As epoxy composite's frequency response characteristics and sensitivity to moisture intrusion are still unknown, its application as the insulation materials of medium-frequency transformers under hygrothermal conditions is limited. This paper investigates the mechanism of moisture intrusion damage to the molecular structure of the epoxy resin matrix and its cross-linking points with the curing agent. The regularity of medium-frequency insulation performance degradation of epoxy composites after hygrothermal aging is studied. Results indicate that after 40 days of hygrothermal aging, moisture together with high temperature damaged the main chain of the epoxy resin and its cross-linking points with the curing agent, resulting in a 23 °C decrease in the glass transition temperature and an 82 % decrease in cross-linking density of the epoxy composite. Moisture ionization and the increase of carriers due to epoxy resin hydrolysis lead to an increase in the amount of space charge. The temperature rise caused by dipole steering polarization facilitates the formation of internal conductive pathways in the epoxy composite, resulting in a 73 % decrease in the medium-frequency breakdown strength and a four-order magnitude decrease in the medium-frequency volume resistivity of the epoxy composite. This study can guide the insulation design of high-reliability medium-frequency transformers.

Hydrothermal aging of carbon fiber reinforced polymer rods intended for cable applications in civil engineering

Carbon fiber reinforced polymer (CFRP) composites have become increasingly popular due to their high strength-to-weight ratio and excellent mechanical properties. However, CFRP composites are susceptible to hydrothermal aging when used as cable applications in civil engineering, which can cause irreversible damage to their service performance. In this study, the effects of water immersion (water@60 °C), constant temperature and humidity exposure (95%RH@60 °C), and alternating hydrothermal environment (12h_60 °C&12h_25 °C@95%RH) were investigated on the property degradation of the CFRP rods. In addition, the water absorption behavior, and thermal and mechanical properties of the CFRP rods were systematically analyzed and compared. We found that elevated temperature and humidity accelerated the water absorption process, resulting in to the higher equilibrium moisture content and diffusion coefficient. Hydrothermal exposure led to maximum degradation in the tensile strength, three-point bending strength and short-beam shear strength of CFRP rods, with values reaching 4.8%, 17.4% and 24.3% in the water@60 °C, 95%RH@60 °C, and 12h_60 °C&12h_25 °C@95%RH conditions, respectively. Among the three mechanical performance properties analyzed, the tensile strength degradation of the CFRP rods was least affected by the three environmental conditions, primarily due to the tensile direction along the carbon fibers. In addition, the three-point bending and short-beam shear strength values of the CFRP rods showed the greatest degradation in the 12h_60 °C&12h_25 °C@95%RH environment. The long-term effects of the water molecules against the CFRP rods in the hydrothermal environment caused resin hydrolysis and debonding of the fiber-matrix interface, leading to degradation in three-point bending and short-beam shear strength. Additionally, the temperature alternating factor accelerated the degradation of the mechanical properties of the CFRP rods, and the mechanical properties of the CFRP rods declined most noticeably with alternating temperatures under the same moisture content conditions.

Improving corrosion resistance of BFRP bars by coating CNTs modified resin in simulated pore solution of seawater sea sand concrete

The corrosion of basalt fiber-reinforced polymer (BFRP) bars restricts their use in alkaline concrete structures. However, developing high-performance resin can improve the anti-alkaline corrosion of BFRP bars. This work investigates the alkaline resistance of BFRP bars by coating carbon nanotubes (CNTs) modified epoxy resin incorporating varying CNTs contents (0, 0.1, 0.3, and 0.5 wt%). The durability of untreated and treated BFRP bars with CNT-modified resin was evaluated using water uptake, transverse shear, and interlaminar shear tests. Scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) were also used to observe the surface corrosion morphology and interior deterioration of BFRP bars, respectively, while Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were applied to analyze the resin deterioration of BFRP bars. It was found that CNTs modified resin can significantly improve the alkaline resistance of BFRP bars. After 180 d of immersion, the interlaminar shear strength (ILSS) retention of untreated BFRP bars is 31.8%, while it is 63.3, 75.0, 91.3, and 93.7% for BFRP bars treated with 0, 0.1, 0.3, and 0.5 wt% CNTs modified resin, respectively. The improvements in ILSS retention of BFRP bars treated with 0.5 wt% CNTs modified resin are 61.9% and 30.4% more than untreated and pure resin-treated BFRP bars, respectively. BFRP bars treated with 0.3 and 0.5 wt% CNTs modified resin exhibit insignificant resin hydrolysis and less porosity than untreated BFRP bars. The effective prevention of hydroxyl ions into the interior of BFRP bars and the enhancement of the anti-crack behavior of resin by CNTs are the leading causes of corrosion resistance improvement in BFRP bars. The outcomes of this study provide insights into using CNTs modified resin to improve the durability of BFRP bars in marine concrete structures.

Applications of collagen extrafibrillar demineralization in dentin bonding

The existing dentin bonding systems based on acid-etching technique lead to the loss of both extrafibrillar and intrafibrillar minerals from dentin collagen, causing excessive demineralization. Because resin monomers can not infiltrate the intrafibrillar spaces of demineralized collagen matrix, degradation of exposed collagen and resin hydrolysis subsequently occur within the hybrid layer, which seriously jeopardizing the longevity of resin-dentin bonding. Collagen extrafibrillar demineralization can effectively avoid the structural defects within the resin-dentin interface caused by acid-etching technique and improve the durability of resin-dentin bonding, by preserving intrafibrillar minerals and selectively demineralizing extrafibrillar dentin. The mechanism and research progress of collagen extrafibrillar demineralization in dentin bonding are reviewed in the paper.

Durability of BFRP bars embedded in seawater sea sand coral aggregate concrete in simulated seawater environment: Effects of coral coarse aggregate and cement contents

This study evaluates the influences of coral coarse aggregate (CCA) and cement contents on the durability performance of basalt fiber-reinforced polymer (BFRP) bars embedded in seawater sea sand coral aggregate concrete (SSCC). The evaluation is conducted by characterizing the changes in interlaminar shear strength after accelerated exposure in a simulated seawater environment. Accelerated aging tests were conducted under varying exposure durations (60, 120, and 180 days) and temperatures (25, 40, and 55 °C). The 1H low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy analyses were conducted to investigate the deterioration mechanisms of embedded BFRP bars. It was found that SSCC-embedded BFRP bars typically have a lower interlaminar shear strength than that of seawater sea sand concrete (SSC)-embedded BFRP bars subjected to the same immersion conditions. This is mainly attributed to the high porosity of CCA, resulting in higher permeability of SSCC than that of SSC. In addition, increasing cement content enhances the initial amount of OH– in SSCC, expands the pitting area of BFRP bars, and maintains OH– concentration better in the exposure tests, accelerating the interlaminar shear strength deterioration of BFRP bars. Microstructure analysis clearly reveals that the deterioration of embedded BFRP bars is mainly caused by resin hydrolysis, fiber-resin interface debonding, and fiber damage after corrosion. Based on the Arrhenius relationship, accelerated aging test results were utilized to predict the service life of SSCC-embedded BFRP bars under the real service condition. The findings of this study are valuable for the application of BFRP bars reinforced SSCC structures under marine environments and provide some insights into improving the long-term performance of SSCC-embedded BFRP bars, i.e., modifying the CCA to minimize the permeability of SSCC and producing low-alkalinity SSCC.

Static and dynamic tensile behaviors of BFRP bars embedded in seawater sea sand concrete under marine environment

Basalt fiber reinforced polymer (BFRP) bars can be used as an appropriate substitute for steel rebars in marine concrete structures due to their corrosion-free nature and high tensile performance. However, the long-term dynamic properties of BFRP bars in the marine environment are not well known, which is critical for structural safety when subjected to external dynamic loads (e.g., tsunamis and earthquakes). Therefore, this study investigates the static and dynamic tensile behaviors of BFRP bars after exposure to the seawater sea sand concrete (SWSSC) under marine environment. Accelerated corrosion tests were conducted under various exposure periods (60, 90, and 120 days) and temperatures (25, 40, and 55 °C). Both optical stereo microscope (OSM) and scanning electron microscope (SEM) were used to examine the failure patterns of BFRP bars, whereas the degradation mechanisms were investigated by X-ray micro-computed tomography (micro-CT), SEM, and Fourier transform infrared spectroscopy (FTIR). Results show that the tensile properties of BFRP bars are sensitive to strain rate. Both the tensile strength and the elastic modulus of BFRP bars increase with increasing strain rate, but the failure strain drops. The tensile strength and failure strain reduce with increasing exposure temperature and duration, whereas the elastic modulus does not change significantly. Microstructure analysis clearly reveals that failures of BFRP bars occur due to fiber breakage, matrix cracking, and interface debonding. The basalt fibers always exhibit brittle fracture, but the fracture surfaces change from relatively flat to rough when the strain rate increases. Moreover, the deterioration of BFRP bars is caused by resin hydrolysis, fiber-resin interfaces debonding and fiber damage after corrosion. These results can provide some insights to promote the application of BFRP composites in coastal and marine structures.

Mechanical degradation and corrosion characterization of riveted joints for CFRP/Al stacks in simulated marine environments

Mechanical performance and durability of CFRP/aluminum joints in accelerated corrosion environment have to be considered before designing composite-metallic hybrid structures. In this work, the corrosion behavior and mechanical properties of CFRP/aluminum stacks and riveted joints were evaluated by cyclic salt spray tests to simulate marine environments. The rivet head and aluminum substrate in coupled region experienced severe galvanic corrosion with heavy formation of corrosion products. CFRP laminate suffered substantial matrix swelling and even resin hydrolysis after continuously exposing to moisture environments. Joint strengths fluctuated very slightly while failure displacement gradually increased when interfacial corrosion between CFRP/Al stacks occurred. Corrosion products were identified by several characterization techniques with the corresponding corrosion mechanisms. In general, this work is expected to bring new knowledge to understand corrosion behavior and durability of rivet joints for the CFRP/Al stacks in accelerated corrosion environments and provide experimental results for benchmarking in particular designing CFRP-strengthened aluminum structures.

Combined effects of sustained bending loading, water immersion and fiber hybrid mode on the mechanical properties of carbon/glass fiber reinforced polymer composite

Fiber reinforced polymer composites have great potential to replace steel for bridge cables, underground oil extraction and ocean engineering owing to light weight, high strength and desirable corrosion and fatigue resistances. How to reduce the material cost and improve the durability through the reasonable material design is significant to promote the engineering application. In the present paper, two kinds of carbon/glass fiber hybrid plates were developed including the fiber random hybrid (RH) and core–shell hybrid (CH) modes. The exposure of sustained bending loading and water immersion as long as 360 days was conducted to investigate the effect of fiber hybrid mode and bending loading on the mechanical properties. The results showed the synergetic effects between the carbon and glass fibers can be fully developed through the random fiber hybrid mode. Furthermore, the incongruous bearing behavior and stress concentration of carbon/glass fiber/resin interface were largely relieved, which contributed to higher mechanical properties. Compared to CH plate, the maximum increase percentages of tensile and flexural strength for RH plate after 360 days were 51.3% and 39.7%, respectively. Higher bending loading level resulted in the fast formation of microcracks, which provided more storage space for the water molecule and accelerated the resin hydrolysis and interface debonding of fiber/resin. Finally, the long-term life prediction of hybrid plate in three typical bridge service environments showed the RH plate has superior corrosive resistance compared to CH plate. The retentions of tensile and flexural strength for the service time of five years were close to 30–40% and 50–60%, which provided the durability guideline based on fiber hybrid design for the engineering applications.

Deterioration of mechanical properties of basalt/carbon hybrid FRP bars in SWSC under seawater corrosive environment

Basalt fibre-reinforced polymer (BFRP) bars are becoming potential substitutes as reinforcements in seawater sea-sand concrete (SWSC). Unidirectional basalt/carbon hybrid fibre-reinforced polymer (HFRP) bars consisting of carbon and basalt fibres have better durability than those of BFRP bars. To examine the hybridisation effects of carbon fibres on the mechanical properties of BFRP bars, herein, the BFRP and HFRP bars embedded in SWSC and normal concrete (NC) were exposed to seawater. Correlations between the tensile properties, Cl− contents, matrix digestions, and microstructural characteristics of FRPs were investigated. Results showed that HFRP bars had higher mechanical properties and durability than those of the BFRP bars. The HFRP bars exhibited a different failure mode from that of the BFRP bars. Degradation rates of the tensile strengths of BFRP and HFRP bars in SWSC were higher than those in NC. Hydrolysis of resin played a dominant role in the degradation of HFRP bars. Alkali silica reaction between the alkali ions in SWSC and silica in the basalt fibres also degraded the HFRP bars. According to the findings of this study, the HFRP bars have better durability than those of the BFRP bars duo to the excellent mechanical properties and better corrosion-resistance of carbon fibres.

Mitigating the deterioration of BFRP bars in seawater sea sand mortar by reducing alkalinity

The susceptibility of BFRP bars in alkaline cementitious environment restricts their application as reinforcing materials in marine construction. To address this problem, the internal alkalinity of seawater sea sand mortars (SWSSM) is controlled in this study through optimization of cementitious materials for the durability enhancement of BFRP bars Accelerated aging tests were conducted to evaluate the durability of BFRP bars embedded in normal and low-alkalinity SWSSM. The mechanical and physiochemical deterioration of the embedded BFRP bars under various exposure periods (3, 6, and 8 months) and temperatures (25, 40, and 55 °C) were studied through interlaminar shear strength test, Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. At 25 °C, the interlaminar shear strength retentions after 240-day exposure for BFRP bars embedded in low-alkalinity SWSSMs with pHs of 11.6 and 11.1 are 4.76 % and 7.20% greater than those of in normal SWSSM (pH of 12.5), respectively. The interlaminar shear strength retentions of BFRP samples in the low-alkalinity groups are 24.71% and 24.54% more than those in the high-alkalinity group at 40 °C, and 45.64% and 41.98% more at 55 °C, respectively. The enhancing effect can be more significant under higher exposure temperature for normal SWSSM, but not for the low-alkalinity SWSSMs. The low-alkalinity SWSSMs help to minimize the degradation of embedded BFRP bars by reducing resin hydrolysis and fiber-resin interface debonding. Moreover, the model of Arrhenius theory predicts that the interlaminar shear strength retention of BFRP bars embedded in the normal SWSSM will decrease to 70% less than 2 years, while that of those embedded in low-alkalinity SWSSMs will maintain more than 80%. This study provides insights into using low-alkalinity cementitious materials to mitigate the deterioration of embedded BFRP bars and to extend their service life in marine concrete structures.

Effects of mixed acid solution on bromide epoxy vinyl ester and its glass fiber reinforced composites

Abstract As fiber reinforced plastics (FRP) have been increasingly widely used, they may sometimes come into contact with several corrosive media simultaneously, for example, the condensate in the smokestack liners of coal-fired power FGD systems. To study the long-term performance and degradation mechanism of FRP in these complicated environments, an accelerated aging test of bromide epoxy vinyl ester (Br-VE) and its glass fiber reinforced composites (GF/VE) in a mixed acid solution(H2SO4, HNO3, HF and HCl) at three different temperatures(25, 55 and 80 °C) for 180 days was carried out. Weight changes, flexural properties, Fourier transforming infrared spectra (FTIR), dynamic thermal mechanical (DMA), macroscopic and microscopic morphology were investigated. Results showed that immersion temperature has important effects on the corrosion behavior of specimens. The long-term weight change behavior of GF/VE at normal temperature was in accordance with Fick’s second law, but deviated at higher temperature. Flexural properties of GF/VE declined more drastically than those of Br-VE at elevated temperatures. The Tg of GF/VE decreased with rising temperatures. Results also indicted that Br-VE and GF/VE manifested varied degradation mechanisms when subject to the same mixed acid medium immersion. The degradation of GF/VE mainly involved plasticization, embrittlement, the hydrolysis of resin, an ion exchange between HF, H+ and Si-O-Si or alkali metal of the fiber as well as the debonding of the resin/fiber interface.

Towards a Non-Biased Formaldehyde Quantification in Leather: New Derivatization Conditions before HPLC Analysis of 2,4-Dinitrophenylhydrazine Derivatives.

In leathers, formaldehyde is currently analyzed according to EN ISO 17226-1 standard, by reversed phase liquid chromatography after off-line precolumn derivatization with 2,4 dinitrophenylhydrazine (DNPH) in strong acidic conditions. We first demonstrate that this standard is not adapted to leather retanned with resins likely to release formaldehyde by hydrolysis. Indeed, formaldehyde content may be largely overestimated due to concomitant resin hydrolysis (in harsh acidic conditions) that releases formaldehyde during the derivatization step and during the waiting time on autosampler before analysis. Therefore, we thoroughly studied the derivatization step in order to propose new derivatization conditions. Replacing orthophosphoric acid by less acidic buffer solutions is not enough to avoid hydrolysis. A derivatization without adding acid is realized by solubilizing DNPH in acetonitrile instead of orthophosphoric acid. These conditions lead to a complete derivatization of formaldehyde in 3 h at 50 °C (in a water bath) while avoiding the hydrolysis of co-extracted dicyandiamide and melamine resins. The as-obtained leather extracts are stable over time. Formaldehyde contents found with this method agree with the formaldehyde content measured immediately at the end of derivatization reaction in standard conditions or with formaldehyde content measured by a home-designed flow injection analysis with acetylacetone online derivatization and UV detection.

Mechanical property evolution and service life prediction of pultruded carbon/glass hybrid rod exposed in harsh oil-well condition

A glass fiber shell (GFS) and carbon fiber core (CFC) hybrid rod (HFRP) was produced through pultrusion technology for an alternative to traditional steel sucker rod for petroleum production. The mechanical properties of a really used HFRP rod closed to the ground (25 °C exposed temperature, 0.5 MPa hydraulic pressure and ~70 kN cyclic loading) and in the deep oil-well up to 2600 m (90 °C exposed temperature, 18 MPa hydraulic pressure and ~50 kN cyclic loading) were investigated as a function of service time as long as 553 days. The mechanical, thermal properties and microanalysis tests of HFRP rods were conducted to obtain the long-term evolution of HFRP rods under the above service environments. Exposure closed to the ground caused a maximum degradation rate of short beam shear strength (SBSS) up to 18.92%. Meanwhile, the maximum degradation rates of interface shear strength (ISS) were 28.24% for carbon fiber/resin, 16.88% for glass fiber/resin and 36.07% for CFC/GFS interface. In comparison, exposure in the deep oil-well brought in an extra degradation rate from 4.34% to 11.11% for ISS, and the higher cyclic loading (~70 kN) played an insignificant effect on the degradation. The degradation mechanism of mechanical properties for HFRP rods was attributed to plenty of bound water combined with the resin through the hydrogen bond and brought about the hydrolysis of resin and the increase of pore volume content (~5%), leading to the debonding of fiber/resin. The long-term prediction of interface shear strength shows the degradations of CFC and CFC/GFS were more sensitive to the cyclic load (70 kN) compared to no cyclic load (0 kN), and an extra degradation rate up to 31.3% was observed compared to the no load condition, and the accelerated degradation was weakened with the increase of service temperature and hydraulic pressure. In addition, the exposure at the increased service temperature and hydraulic pressure in the deep oil-well led to an additional degradation rate of ISS in comparison to the ground exposure: 10.70% (CFC), 13.25% (CFC/GFS) and 4.81% (GFS).

Maximizing the functional lifetime of Protein A resins.

Protein A chromatography is currently the industry gold-standard for monoclonal antibody and Fc-fusion protein purification. The high cost of Protein A, however, makes resin lifetime and resin reuse an important factor for process economics. Typical resin lifetime studies performed in the industry usually examine the effect of resin re-use on binding capacity, yield, and product quality without answering the fundamental question of what is causing the decrease in performance. A two part mechanistic study was conducted in an attempt to decouple the effect of the two possible factors (resin hydrolysis and/or degradation vs. resin fouling) on column performance over lifetime of the most commonly used alkali-stable Protein A resins (MabSelect SuRe and MabSelect SuRe LX). The change in binding capacity as a function of sodium hydroxide concentration (rate of hydrolysis), temperature, and stabilizing additives was examined. Additionally, resin extraction studies and product cycling studies were conducted to determine cleaning effectiveness (resin fouling) of various cleaning strategies. Sodium hydroxide-based cleaning solutions were shown to be more effective at preventing resin fouling. Conversely, cold temperature and the use of stabilizing additives in conjunction with sodium hydroxide were found to be beneficial in minimizing the rate of Protein A ligand hydrolysis. An effective and robust cleaning strategy is presented here to maximize resin lifetime and thereby the number of column cycles for future manufacturing processes. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:708-715, 2017.

The effect of humidity on formaldehyde emission parameters of a medium-density fiberboard: Experimental observations and correlations

Initial emittable concentration (C0), diffusion coefficient (Dm) and partition coefficient (K) are the three key emission parameters determining formaldehyde emissions from “dry” building materials. Previous studies of humidity effect on formaldehyde emissions were mainly focused on the analysis of steady-state emission rates or concentrations, whereas humidity effects on emission parameters were seldom discussed. In this study, we measured formaldehyde emissions of a medium-density fiberboard in a dynamic small-scale environmental chamber at the relative humidity (RH) of 20%, 30%, 50% and 80%, respectively. Emission parameters were estimated and the effects of humidity were analyzed. C0 was the most sensitive parameter influenced by humidity, which increased 2.97-fold when RH changed from 20% to 80%. Empirical positive linear relations between C0 and RH, C0 and absolute humidity (AH) were identified. Differences of Dm and K between each humidity scenarios were within 11% and 17%, suggesting the negligible impacts of humidity on them. Moreover, the reversible and simultaneous responses of formaldehyde emissions to humidity changes were exhibited in experiments. Possible mechanisms of humidity effect on formaldehyde emission were hydrolysis of resins or polymers and adsorption competitions between formaldehyde and water molecules. The conclusions and empirical relations obtained in this study would be useful in understanding emission parameters at different humidity conditions.

Defying ageing: An expectation for dentine bonding with universal adhesives?

ObjectivesThe present study evaluated the long-term dentine bonding effectiveness of five universal adhesives in etch-and-rinse or self-etch mode after 12 months of water-ageing. MethodsThe adhesives evaluated included All-Bond Universal, Clearfil Universal Bond, Futurabond U Prime&Bond Elect and Scotchbond Universal. Microtensile bond strength and transmission electron microscopy of the resin-dentine interfaces created in human coronal dentine were examined after 24h or 12 months. ResultsMicrotensile bond strength were significantly affected by bonding strategy (etch-and-rinse vs self-etch) and ageing (24h vs 12 months). All subgroups showed significantly decreased bond strength after ageing except for Prime&Bond Elect and Scotchbond Universal used in self-etch mode. All five adhesives employed in etch-and-rinse mode exhibited ultrastructural features characteristic of collagen degradation and resin hydrolysis. A previously-unobserved inside-out collagen degradation pattern was identified in hybrid layers created by 10-MDP containing adhesives (All-Bond Universal, Scotchbond Universal and Clearfil Universal Bond) in the etch-and-rinse mode, producing partially degraded collagen fibrils with intact periphery and a hollow core. In the self-etch mode, all adhesives except for Prime&Bond Elect exhibited degradation of the collagen fibrils along the thin hybrid layers. The three 10-MDP containing universal adhesives did not protect surface collagen fibrils from degradation when bonding was performed in the self-etch mode. ConclusionsDespite the adjunctive conclusion that bonds created by universal adhesives in the self-etch bonding mode are more resistant to decline in bond strength when compared with those bonds created using the etch-and-rinse mode, bonds created by universal adhesives are generally incapable of defying ageing.

Durability of glass fiber-reinforced polymer composites under the combined effects of moisture and sustained loads

This paper deals with durability of glass fiber-reinforced polymer composites under sustained loads and simultaneously exposed to either saltwater or tap water. The tensile properties of the specimens before and after conditioning were evaluated along with their moisture uptaking behavior to reveal the durability of the specimens under combined effects. The mass change curves under saltwater and tap water immersion exhibited dual-stage diffusion process. The first stage followed Fickian profile, while mass loss occurred in the second stage with increasing immersion time, attributed to hydrolysis of resin. The weight gain in saltwater was greater than that in tap water. Moreover, the mass change curves under varying percentage of sustained loadings exhibited similar trends, while the maximum moisture uptake was obviously affected by the loading conditions. Based on Fick’s second law, the diffusion coefficients in the first stage under different conditions were determined through the least-square regression technique. It was observed that the tensile strength and modulus were increasing initially upon immersion, which was attributed to curing beyond the initial cure during manufacture. Then, the tensile properties decreased with continued immersion in saltwater or tap water. After 180 days of immersion, the tensile properties degraded at a smaller rate, both for specimens with and without sustained loading. For the saltwater immersion of 360 days, the tensile properties decreased significantly as the sustained loading increased. However, the tap water immersion had less detrimental effect on tensile properties of glass fiber-reinforced polymer. Furthermore, based on Arrhenius concept coupled with fracture mechanics principle, a new model was proposed to describe the combined effects of immersion and sustained load.

The mechanically contaminated layer theory of sand-filled fibreglass-reinforced polyester pipes: An explanation of the initial process for the mechanical and hydrolytical behaviour of massive pipeline failures

This investigation describes the fracture mechanism which explains a significant part of massive failures due to the existence of a sand layer placed near the neutral axis in the core making the composite very sensitive to impacts in fibreglass-reinforced polyester pipes. These failures create interface delamination, and consequently fluid can leak into supporting sand backfill thereby initiating the fracture process that can, at times include resin hydrolysis. In order to assess the delamination magnitude, an analytic method is developed and a squared root law between delamination and energy applied proposed. Vertical blunt ram tests on samples extracted from complete pipes have been carried out to verify this theory, reaching a goodness of fit up to 92%. It is concluded that low-energy impacts, around 90–160 J in 800–1000 diameter PN 16–20 continuous filament winding pipes, can seriously compromise their structural integrity with no external trace.

Manufacture of cellulose nanocrystals by cation exchange resin-catalyzed hydrolysis of cellulose

Cellulose nanocrystals (CNC) were prepared from microcrystalline cellulose (MCC) by hydrolysis with cation exchange resin (NKC-9) or 64% sulfuric acid. The cation exchange resin hydrolysis parameters were optimized by using the Box–Behnken design and response surface methodology. An optimum yield (50.04%) was achieved at a ratio of resin to MCC (w/w) of 10, a temperature of 48°C and a reaction time of 189min. Electron microscopy (EM) showed that the diameter of CNCs was about 10–40nm, and the length was 100–400nm. Regular short rod-like CNCs were obtained by sulfuric acid hydrolysis, while long and thin crystals of cellulose were obtained with the cation exchange resin. X-ray diffraction (XRD) showed that, compared with MCC, the crystallinity of H2SO4-CNC and resin-CNC increased from 72.25% to 77.29% and 84.26%, respectively. The research shows that cation exchange resin-catalyzed hydrolysis of cellulose could be an excellent method for manufacturing of CNC in an environmental-friendly way.

Hydrolyse von Harnstoff-Formaldehyd-Harzen: Auflösung des Spangefüges in Holzwerkstoffen durch hydrolytischen Abbau der Leimfuge

The hydrolytic degradation of urea-fomaldehyde resins (UF) has gained new relevance since the development of procedures for reuse of particle- and fibre-boards based on steam hydrolysis. In Germany, today 100,000 tons of used particleboards are recycled by thermo-hydrolytical processes annually. This work points out the role of resin hydrolysis in these recycling processes. Therefore, the behaviour of ground particleboards as well as pure, hardened UF resin under hydrolytic conditions was investigated. Influences of temperature and pH value were assessed to estimate their effect on the hydrolysis process.