Curable Materials Research Articles

Evolution of material properties during the solvent-assisted recycling of thermosetting polymers: to reduce the residual stress and material inhomogeneity

Primary recycling of thermosetting polymers is shown to be enabled by depolymerizing the material in a suitable organic solvent and then re-polymerizing it into near-identical networks with equivalent mechanical properties. The re-polymerization process involves sophisticated coupling among solvent diffusion, chemical reaction, and stress field development. Specifically, solvent evaporation leads to restrained volume shrinkage of the resin and residual stress development within the re-polymerized materials. Nonuniform curing degree and material properties are also developed in the direction of solvent diffusion. These impose grand challenges to identify the optimal processing conditions to recycle thermosets with high quality and high speed. In this paper, using an integrated experimental and theoretical approach, the evolutions of the stress field and material properties during the re-polymerization of thermosetting polymers are studied. It shows how to tune the processing temperature to mitigate the residual stress and material inhomogeneity of recycled thermosets. The influencing mechanisms of sample thickness and catalyst content are also revealed. The fundamental understanding is finally extended to study the manufacturing of composites with particle reinforcements using the depolymerized solution, with a particular emphasis on the minimization of the stress concentration around particles. Overall, this study provides a guideline to design material and processing conditions for homogeneous network structure and mechanical properties of recycled thermosets, which will promote the applications of the green recycling method for thermoset wastes and benefit society.

The molecular weight and curing dynamics of bisphenol a expansion chain modified epoxy resin affect the physical and electrical properties of their curing materials

The molecular weight and curing dynamics of bisphenol a expansion chain modified epoxy resin affect the physical and electrical properties of their curing materials

Hydration and pore structure characteristics of concrete incorporating internal curing materials in a dry and large-temperature-difference environment

The climate in the Central Asian area is extreme dry, with a large temperature difference between day and night, and the concrete is easy to crack during the construction period under the conditions of traditional external curing. Therefore, this study concerns understanding the application of internal curing materials in a dry and large-temperature-difference environment. The effects of three internal curing materials, namely, Super Absorbent Polymer (SAP), Light Weight Aggregate (LWA) and Perforated Cenospheres (PCs), on hydration and pore structure characteristics of concrete were investigated. Scanning electron microscope (SEM) and x-ray diffractometer (XRD)were used to observe the microscopic morphology and physical phase composition of concrete, and the evolution of pore characteristics was analyzed using mercury intrusion porosimeter (MIP) to explore the mechanism of pore structure refinement. Results show that the pores formed by the release of water provide space for the accumulation of hydration products, thereby accelerating the formation of ettringite crystals. Results indicate that the continuous release of internal curing materials allows the interior of the concrete to continue to be hydrated, which greatly promotes the overall hydration of the cement. The effect of supplementary cementitious materials (GGBS, FA) and implications of large-temperature-difference environment on concrete durability are discussed.

Microfluidic fabrication of novel polymeric core‐shell microcapsules for storage of CO2 solvents and organic chelating agents

AbstractMonodispersed polymeric microcapsules loaded with CO2 solvents or chelating agents were produced by capillary microfluidics by photopolymerisation of three different UV curable materials, 1,6‐hexanediol diacrylate (HDDA), Norland Optical Adhesive (NOA) 81, and Semicosil® 949 UV A/B (PDMS). Polymerization of HDDA and NOA 81 started after exposure to UVA light for 5 s and was completed within a minute, as confirmed by continuous FT‐IR. Corrosive aqueous solutions of tetraethylenepentamine and diisopropyl iminodiacetic acid were encapsulated with 100% efficiency into poly(HDDA) and cured NOA81 shells without any leakage during prolonged storage. Poly(HDDA) shells were mechanically more stable than cured NOA81 and PDMS shells and resistant to drying‐induced shell buckling. NOA81 and PDMS capsules underwent morphological changes during freeze drying leading to the formation of dimpled and crescent‐moon‐shaped particles, respectively. The storage stability in a hypotonic solution and buckling resistance of PDMS shells were significantly improved by embedding carbon‐based nanomaterials into PDMS matrix. The incorporation of 0.5 wt% multi‐walled carbon nanotubes into PDMS matrix led to an increase in a Shore A hardness from 1.6 to 2.3. A uniform distribution of MWCNTs in the polymer network was confirmed by XRD. All fabricated shells were thermally stable up to the temperature of 300°C.

Highly transparent acrylate epoxidized soybean oil based UV–curable silicone–modified coatings with good thermal stability and flame retardancy

Thermal stability, flame retardancy and transparency are essential for UV–curable materials serving as package materials for some optical or electronics devices. In this paper, acrylate epoxidized soybean oil (AESO) based UV–curable silicone modified coatings with good thermal stability, good flame retardancy, transmittance above 97% were fabricated by UV initiated thiol–ene reaction of AESO and thiol silicone resin. The thermal stability of AESO–based UV–curable silicone–modified coatings is better than that of neat AESO–based UV–curable coatings reported previously, because the thermal initial decomposition temperature (Td5) of the former is in the range of 313–322 °C while that of the latter is only in the range of 214–283 °C. Cone calorimetry test denotes AESO–based UV–curable silicone–modified coatings possess good flame retardancy because the maximum value of the heat release rate (HRR) and CO release (CO Yield) for AESO–based UV–curable silicone–modified coatings are 450–550 kW/m2 and 0.02%–0.33%, respectively. The mechanism for the improvement of flame retardancy was studied by scanning electron microscope (SEM) analysis of the surface morphology of the chars after being burned.

Effect of water‐to‐cement ratio on internal relative humidity and autogenous shrinkage of early‐age concrete internally cured by superabsorbent polymers

AbstractSelf‐desiccation is one common phenomenon of concrete with low water‐to‐cement (w/c) ratios, which may lead to the decrease of internal relative humidity (IRH), and therefore causing autogenous shrinkage (AS). Superabsorbent polymers (SAPs) are used as a kind of internal curing material to mitigate AS of concrete. The IRH and AS are significantly affected by the w/c ratio, and several attempts have been made to investigate the IRH or AS of concrete with different w/c ratios. However, the prediction model of AS considering IRH and w/c ratio of internally cured (IC) concrete is limited. In the present study, the effect of w/c ratio on IRH and AS of IC concrete was investigated, and a two‐stage prediction model of AS based on the results of IRH for IC concrete considering the effect of w/c ratio was proposed. The experiment results and analysis indicated that IRH of IC concrete increased as increase of w/c ratio, and development of IRH experienced two stages: a water‐vapor saturated stage with 100% RH (stage I), and a gradually reducing stage in which IRH decreased gradually (stage II); critical time of IC concrete increased as increase of w/c ratio; expansion peak of IC concrete increased as increase of w/c ratio; AS and AS rate of IC concrete decreased as increase of w/c ratio; IRH, critical time, and expansion peak of IC concrete were higher than that of ordinary concrete; AS and AS rate of IC concrete were lower than that of ordinary concrete.

Application of Pre-Wetted High Titanium Heavy Slag Aggregate in Cement Concrete.

High titanium heavy slag is one kind of solid waste that exists in large amounts in the southwest of China. In this paper, this high titanium heavy slag is used as natural pre-wetted material in concrete because of its porous structure. Three kinds of aggregates are used in this concrete. The first one is natural limestone and river sand. The second one is dry slag fine aggregate and coarse aggregate. The third one is pre-wetted coarse slag aggregate and dry slag fine aggregate. The strength, dry shrinkage, autogenous shrinkage, relative humidity, pore size distribution, stress–strain relationship, micro-hardness and chloride penetration of concrete composed of the above three aggregates are tested in this study. The results show that pre-wetted slag aggregate is a suitable internal curing material. The concrete with pre-wetted slag aggregate shows higher strength, lower shrinkage and smaller porosity. The water absorbed in the slag aggregate can be released effectively to increase the relative humidity, accelerate hydration, improve porosity and increase the interface strength.

Effects of recycled ceramic aggregates on internal curing of high performance concrete

High performance concrete (HPC) is widely used in concrete structures because of its excellent mechanical properties, good workability, and outstanding durability. However, as HPC usually has a low water to cement ratio, the hydration of cement would cause rapid decrease in the humidity inside concrete, leading to autogenous shrinkage of HPC. Internal curing is a method to maintain the internal humidity of concrete by introducing water storage materials into HPC. In this study, three different waste ceramic aggregates are employed as internal curing materials for HPC. The physical properties and the chemical compositions of the three ceramic materials are studied through microscopic tests. The internal curing efficiency is then investigated through mechanical tests and autogenous shrinkage tests of HPC. The experimental results show that the properties of HPC are greatly affected by the porosity and replacement ratio of the ceramic aggregate. A better shrinkage control can be achieved by using the aggregate with larger porosity, while higher strength is obtained when the replacement ratio is lower. In general, all three recycled ceramic aggregates are highly efficient in reducing autogenous shrinkage of HPC while maintaining a satisfactory level of mechanical properties, and wall tile with 20% replacement ratio is considered to perform the best.

Effect Of Attapulgite as Internal Curing in High-Performance Concrete with Variable Temperature Curing to Enhance Mechanical Properties

One of the most important elements in the development of compressive strength is concrete curing, and a large temperature differential during curing may decrease strength. This exudation is caused by microcracks in the concrete caused by the continuous temperature fluctuation. By minimizing autogenous shrinkage, internal curing has become popular for reducing the danger of early-age cracking in high-performance concrete (HPC). The efficacy of internal wet curing provided by fine Attapulgite aggregate is investigated in this research. On three different HPCs, both with and without internal curing materials, the development of observed mechanical properties is investigated. Two different amounts of normal weight fine aggregate were replaced with attapulgite fine aggregates. Internal cure has been found to benefit from attapulgite fine aggregates. It has been found that adding 20% Attapulgite fine aggregates to HPC enhances the material’s characteristics, resulting in low internal stress and a significant increase in compressive strength. It should be noted that, unlike certain conventional lightweight aggregates, the different amounts of Attapulgite fine aggregates added at various ages have shown no decrease in compressive strength.

Effect of partial replacement of fine aggregate by internal curing materials on mechanical properties of concrete

Internal curing has long been utilized to decrease self-shrinkage and consequently the increased danger of concrete cracking prematurely. The measured mechanical characteristics of concrete were studied in five mixes, both with and without internal curing. Two of these mixtures have a 10% replacement rate, with one using ceramic and the other Attapulgite, while the other two have a 20% replacement, with one using ceramic and the other using Attapulgite, and the fifth is a reference mixture with no replacement for comparative reasons. With an increase of 27.93%, the ceramic combination with a 20% replacement rate is judged to have the highest compressive resistance, followed by the Attapulgite mixture with a 20% replacement rate with an increase of 34.2%. The results showed that the ceramic and Attapulgite internal curing purposes were highly effective, especially with a 20% replacement. The use of crushed ceramics and attapulgite as internal curing materials improves the characteristics of concrete.

Influence of Internal Curing Materials on Durability Properties of High-Performance Concrete

Influence of Internal Curing Materials on Durability Properties of High-Performance Concrete

The use of ceramics as an internal curing agent in high performance concrete with variable temperature curing to improve mechanical characteristics

Concrete curing is one of the most significant factors in the development of compressive strength, and a high temperature difference during curing may reduce strength. The microcracks created in the concrete as a result of the constant temperature change cause this exudation. Internal curing has become popular for decreasing the risk of early-age cracking in high-performance concrete by limiting autogenous shrinkage (HPC). This study looks at the effectiveness of internal wet curing offered by a new kind of aggregate called “recycled waste porous ceramic fine aggregates”. The evolution of measured mechanical characteristics is examined on three distinct HPCs, both with and without internal curing materials. Ceramic fine aggregates were used to replace two different quantities of regular weight fine aggregate. Ceramic fine aggregates were shown to be quite beneficial for internal cure. It has been discovered that incorporating 20% ceramic fine aggregates into HPC improves the properties of the material, resulting in low internal stress and a large improvement in compressive strength. It should be emphasized that, unlike some traditional lightweight aggregates, no loss in compressive strength has been seen for the various quantities of ceramic fine aggregates introduced at either early or later ages.

Laser Induced Thermal Effect on the Polymerization Behavior in Upconversion Particle Assisted Near-Infrared Photopolymerization.

Laser induced thermal effect is inevitable in upconversion particle assisted near-infrared polymerization (UCAP). Herein, the influence of thermal effects on the polymerization behavior are investigated. The effects of up-conversion particles content and NIR laser intensity on the polymerization rate and surface oxygen inhibition were systematically investigated, and the temperature evolution and complex viscosity changes in the polymerization system during the polymerization process were also monitored. In addition, polymerization experiments conducted on a controlled temperature platform were used to study the effect of NIR heating on the polymerization behavior. The results show that the near-infrared thermal effect promotes the polymerization reaction, but also causes severe oxygen inhibition which has an adverse effect on polymerization. Finally, NIR curing materials with enhanced mechanical properties than those of conventional UV curing materials were obtained.

Printing Parameter Requirements for 3D Printable Geopolymer Materials Prepared from Industrial Side Streams.

The objective of this investigation is to study the printing parameter requirements for sustainable 3D printable geopolymer materials. Side streams of the paper, mining, and construction industries were applied as geopolymer raw materials. The effect of printing parameters in terms of buildability, mixability, extrudability, curing, Al-to-Si ratio, and waste materials utilisation on the fresh and hardened state of the materials was studied. The material performance of a fresh geopolymer was measured using setting time and shape stability tests. Standardised test techniques were applied in the testing of the hardened material properties of compressive and flexural strength. The majority of developed suitable 3D printable geopolymers comprised 56–58% recycled material. Heating was used to improve the buildability and setting of the material significantly. A reactive recyclable material content of greater than 20% caused the strength and material workability to decrease. A curing time of 7–28 days increased the compressive strength but decreased the flexural strength. The layers in the test samples exhibited decreased and increased strength, respectively, in compressive and flexural strength tests. Geopolymer development was found to be a compromise between different strength values and recyclable material contents. By focusing on specialised and complex-shape products, 3D printing of geopolymers can compete with traditional manufacturing in limited markets.

Design Strategy for Recycled Aggregate Concrete: A Review of Status and Future Perspectives

Currently, a number of disadvantages hampers the use of recycled concrete aggregates (RCA). The current review proves that concretes made with complete replacement of natural aggregate with RCA allow the production of high-quality concrete. One of the possibilities for improving concrete properties with RCA is the use of extended curing and pozzolanic materials with varying cement ratios. The potential use of RCA concretes is in the production of high-value materials that increase environmental and financial benefits. RCA have strong potential in the development of a new generation of concrete and stimulate economic activity in many countries in addition to optimizing natural resources. Economic benefits include minimal travel costs; cheaper sources of concrete than newly mined aggregates; reduction of the landfill area required for the placement of concrete waste; the use of RCA minimizes the need for gravel extraction, etc. The proposed strategy could be to sequentially separate demolition waste such as roof finishes, waterproof materials, interior and exterior materials, etc. Closing life cycles is the main approach used for efficient structures for the recycling and reuse of construction and demolition waste in the production and recovery of materials, especially when recycling and reusing materials. In the life cycle, the recycling of recovered materials allows them to be used for new construction purposes, avoiding the use of natural concrete aggregates. Government, design institutes, construction departments and project managers should be involved in the creation and use of RCA. In demolition and construction, the main players are the project owners. Their obligations, expectations and responsibilities must be properly aligned. For the past 20 years, recycled concrete aggregate from demolition and construction waste has been considered as an alternative to pure concrete in structural concrete to minimize the environmental impact of construction waste and demolition waste and the conversion of natural aggregate resources. It is now recognized that the use of RCA for the generations of concrete is a promising and very attractive technology for reducing the environmental impact of the construction sector and conserving natural resources. In the market, the selling price is not an obstacle for market applications of RCA, as there are scenarios in which their cost is lower than the cost of products made from conventional building materials. This is more of an acceptance factor in the market for recycled concrete aggregates. In this sector, the lack of identification, accreditation and uniform quality certification systems and their narrow application cause some marketing problems. With proper RCA preparation, concrete with standard physical and mechanical properties and performance characteristics can be obtained.

X-ray computed tomography evaluations of additive manufactured multimaterial composites.

Additive Manufacturing (AM) often produces complex engineered structures by precisely distributing materials in a layer-by-layer fashion. Multimaterial AM is a particularly flexible technique able to combine a range of hard and soft materials to produce designed composites. Critically, the design of AM multimaterial structures requires the development of precise three-dimensional (3D) computed aided design (CAD) files. While such digital design is heavily used, techniques able to validate the physically manufactured composite against the digital design from which it is generated are lacking for AM, especially as any evaluations must be able to distinguish material variation across the 3D space. Nowadays, there is a growing interest in volumetric tools that can provide topological information hidden by the surface of shaped materials. So far, technologies such as Optical microscopy (OM), Scanning Electron Microscopy (SEM), and Coordinate Measuring Machine (CMM) have paved the way into the metrology field to measure the external geometry of physical objects. Currently, alongside conventional metrology tools, X-ray computed tomography (XCT) is emerging to measure the subsurface of the objects but maintaining the integrity of the probed samples. Thereby, the volumetric nature of the XCT investigations and its associated imaging techniques, ensure 3D quantitative measurements comparable to the output data from 2D metrology tools, but above all, supply the missing subsurface description for an exhaustive metrology study. The reward associated with XCT applied to multimaterial AM is a map reflecting the fabricated distribution of materials following CAD, with the benefits of better understanding the mechanical interplay within phases, hence, describing the hidden processes as well as the changes in phases due to a range of mechanical or chemical phenomena. In this study, a nondestructive approach using X-ray computed tomography (XCT) is used to fully evaluate the 3D distribution of multimaterials from an AM process. Specifically, two diverse hard and soft materials are alternatively produced in the form of a fibre embedded in a matrix via ink-jet printing. XCT coupled with imaging evaluation were able to distinguish between the differing materials and, importantly, to demonstrate a reduction in the expected fabricated volumes when compared to the respective CAD designs. LAY DESCRIPTION: Additive Manufacturing (AM) has recently become important in producing complex engineered structures. Using 3D CAD files and/or reconstructed data sets from imaging, hard and soft materials are manufactured independently or in combination, according to geometrical features and shapes in the input data. However, the evaluation of the resultant manufactured parts in comparison with the original 3D drawing is currently lacking. In this sense, X-ray computed tomography (XCT) provides an important metrology tool for mono and multimaterial AM. In this work a volumetric metrology investigation is proposed using higher resolution XCT to provide 3D information comparable to that of the 3D CAD drawings. A commercial high-resolution multijetting material printer (ProJet 5500X, 3D Systems, USA) is used to manufacture single fibre composites, through a complementary deposition of photo sensible polymers. Hard and soft plastics are produced using a UV curable step, resulting in materials of similar attenuation under an X-ray probe. A critical aim of the evaluations is the potential for XCT to distinguish between different UV curable 3D printing materials.

Emergence of Polymeric Material Utilising Sustainable Radiation Curable Palm Oil-Based Products for Advanced Technology Applications.

In countries that are rich with oil palm, the use of palm oil to produce bio-based acrylates and polyol can be the most eminent raw materials used for developing new and advanced natural polymeric materials involving radiation technique, like coating resins, nanoparticles, scaffold, nanocomposites, and lithography for different branches of the industry. The presence of hydrocarbon chains, carbon double bonds, and ester bonds in palm oil allows it to open up the possibility of fine-tuning its unique structures in the development of novel materials. Cross-linking, reversible addition-fragmentation chain transfer (RAFT), polymerization, grafting, and degradation are among the radiation mechanisms triggered by gamma, electron beam, ultraviolet, or laser irradiation sources. These radiation techniques are widely used in the development of polymeric materials because they are considered as the most versatile, inexpensive, easy, and effective methods. Therefore, this review summarized and emphasized on several recent studies that have reported on emerging radiation processing technologies for the production of radiation curable palm oil-based polymeric materials with a promising future in certain industries and biomedical applications. This review also discusses the rich potential of biopolymeric materials for advanced technology applications.

Texture analysis of the microstructure of concrete with different concentrations of superabsorbent polymer after internal curing

Internal curing has been widely used in high-strength concrete because it can replenish water for cement hydration and reduce self-shrinkage. The internal curing effects mostly depend on the self-shrinkage changes and mechanical parameters obtained through a destructive test. This research proposes a fast and nondestructive detection method based on image recognition analysis to determine the effects of internal curing material content on the performance of high-strength concrete. The superabsorbent polymer (SAP) was chosen as the internal curing material. Laboratory uniaxial compression tests, scanning electron microscopy (SEM), and energy dispersive spectroscopy were used to analyze the mechanical properties and phase characteristics of the concrete. Based on the SEM images, the gray level co-occurrence matrix was used to extract texture features of the concrete, and effective SEM image samples were screened out to verify the correlation between texture features and mechanical strength. The results showed that: (1) the four characteristic values of GLCM have a significant linear correlation with SAP content; (2) with the increase in SAP content, self-shrinkage decreases and reaches the smallest point when the SAP content is 0.24 % of the cementing material content; and (3) the relative dynamic modulus of elasticity and maximum shrinkage are negatively correlated with the energy and correlation and positively correlated with the contrast and entropy. Such results provide a simple method of determining the influence of internal curing content on concrete performance.

Characterization and microfabrication of natural porous rocks: From micro-CT imaging and digital rock modelling to micro-3D-printed rock analogs

Tests on standard rock specimens with controlled and identical pore structure are critical to validating the analytical and numerical models. However, it is usually difficult to acquire two natural samples with the same internal structure for the destructive laboratory tests, for the sake of the heterogeneity of natural rock which is caused by the complex diagenetic processes. Three-dimensional (3D) printing technology provides an alternative approach to produce geometry-identical, features-controllable, and lab-testable analogs of natural rock from digital data in a faster and more cost-effective way. This paper presents a customized workflow of 3D-printed rock analogs from micro-CT images combining with digital rock modelling. Three types of natural rock specimens are imaged by micro-CT and processed as inputs for two types of 3D printing techniques. Rock analogs are printed at multiple magnifications from original CT volume in five curable resin materials. Petrophysical parameters of 3D-printed rock analogs are acquired through helium pycnometry (HP) and mercury intrusion porosimetry (MIP). The accuracy of 3D-printed rock analogs is evaluated by comparing the measured results with the benchmark data derived from the digital rock modelling. Both the advantages and the current challenges to reproduce the real pore structure of natural rock by the 3D-printed analogs are discussed. The results indicate that the gypsum-based printed analogs are prior to modelling the surface roughness and wettability properties to natural rock grains, while the resin-based printed analogs owe advantages on reproducing pore structure. As the first effort in literature, this study investigates the inherent relationship between digital rock and 3D-printed rock analogs via comprehensive comparison on petrophysical properties. The results approve that the 3D printing technique is a novel, feasible, and alternative approach for laboratory test to generate rock analogs from the digital model of the natural rock. However, it is still difficult to print the pore structure of the rock at the original dimension. • A customized framework of rock analogs 3D printed from micro-CT image was established. • As the first effort in literature, the inherent relationship between digital rock and 3D-printed rock was investigated. • The effects of different printing techniques, materials, and up-scaling factors on reproducing pore structure was discussed.

Renewable UV-curable polyester methacrylate/cellulose nanocrystals composite resin for wood waterproof coating

Low-viscosity UV-curable resins are widely used in industry as they allow for UV curing materials with reduced amounts of reactive diluents to adjust the viscosity. But their mechanical properties and waterproof performance after curing as UV coatings still need to be improved. Here, a series of low-viscosity bio-based UV-curable polyester methacrylates were synthesized through L-lactide (LA) and ε-caprolactone (CL) monomers. The results show that the introduction of star-shaped structure and random copolymerization of LA and CL can effectively reduce the viscosity of the resin to 313 mPa · s and at the same time increase the double bond conversion rate and maintain good mechanical properties. The composite resin was prepared by blending the star-shaped low-viscosity polyester methacrylate resin with cellulose nanocrystals (CNCs), and the microstructure was characterized by XRD and TEM. The curing kinetics, mechanical properties, thermal properties and waterproof properties of the composite resin were further tested. When the mass fraction of CNCs is 2.5 wt%, the water absorption rate of the pine samples coated with UV-cured composite resin is reduced to 17%, which is 65% lower than that of the uncoated samples and 20% lower than that of the samples coated with resin without CNC. This article provides a feasible and effective method for improving the mechanical properties and waterproof performance of low-viscosity UV-curing resins.