Shrinkage Stress Research Articles

Polymerization Shrinkage of Short Fiber Reinforced Dental Composite Using a Confocal Laser Analysis.

The purpose of this study was to investigate the polymerization shrinkage of short fiber reinforced composite (SFRC) using a multicolor confocal displacement laser that can measure the polymerization shrinkage with high accuracy. The three types of SFRCs used in this study were XD (Ever X Flow Dentin), XB (Ever X Flow Bulk), and XP (EverX Posterior). In addition, CF (Clearfil majesty ES Flow) with hybrid type filler was used as a control. The measured values of the final polymerization shrinkage rate and amount of polymerization shrinkage rate when the polymerization shrinkage rate became constant (less than 0.1 µm/s) were approximated for all SFRCs. XP had a large aspect ratio of glass fiber filler and showed a significant difference from XD with a small aspect ratio (p < 0.05). There was no significant difference in the measured value of time when the polymerization contraction reached a constant speed (0.1 µm/s or less) for all SFRCs (p > 0.05). There was no significant difference in the measured values of polymerization shrinkage rate after the polymerization shrinkage reached a constant rate for all SFRCs (p > 0.05). These results show that glass fiber with large aspect ratio can alleviate polymerization shrinkage stress. The polymerization behavior of SFRC was found to be dependent on the amount of glass fiber filler, aspect ratio, and orientation.

Evaluation of a photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition polymer network with improved water stability and high mechanical performance as an ester-free dental restorative

ObjectiveThe objective is to develop and characterize an ester-free ether-based photo-CuAAC resin with high mechanical performance, low polymerization-induced stress compared with common BisGMA/TEGDMA (70/30) resins, and improved water stability in comparison to previously developed urethane-based photo-CuAAC resins. MethodsTriphenyl-ethane-centered ether-linked tri-azide monomers were synthesized and co-photopolymerized with ether-linked tri-alkyne monomers under visible light irradiation using a copper(II) pre-catalyst and CQ/EDAB as the initiator. The ether-based CuAAC formulation was investigated for thermo-mechanical properties, polymerization kinetics and shrinkage stress, and flexural properties with respect to a conventional BisGMA/TEGDMA (70/30) dental resin. In addition, both the ether-based CuAAC resin and the urethane-based CuAAC resin were examined for their water stability using the BisGMA/TEGDMA (70/30) resin as a control. ResultsThe ether-based CuAAC network (AK/AZ-1) exhibited a slightly lower glass-transition temperature compared with the BisGMA/TEGDMA network (108 °C vs 128 °C), but because of its much sharper glass transition, the AK/AZ-1 CuAAC-network maintained storage modulus higher than 1 GPa up to 100 °C. In addition, the ether-based AK/AZ-1 network exhibited reduced shrinkage stress (0.56 MPa vs 1.0 MPa) and much higher flexural toughness (7.6 MJ/m3vs 1.6 MJ/m3) while showing slightly lower flexural modulus and slightly higher flexural strength compared with the BisGMA/TEGDMA network. Moreover, the ether-based AK/AZ-1 CuAAC network displayed comparable water stability in comparison to the BisGMA/TEGDMA network with slightly higher water sorption (46 μg/mm3vs 38 μg/mm3) and much lower water solubility (2.3 μg/mm3vs 4.4 μg/mm3). SignificanceEmploying the ether-based hydrophobic CuAAC formulation significantly improved the water stability of the CuAAC network compared with previously developed urethane-based CuAAC networks. Furthermore, compared with the conventionally used BisGMA/TEGDMA formulation, the reduced shrinkage stress, comparable flexural strength/flexural modulus, and the superior flexural toughness of the ether-based CuAAC network make it a promising ester-free alternative to the currently widely-used methacrylate-based dental restoratives.

Thiol–acrylate based vitrimers: From their structure–property relationship to the additive manufacturing of self-healable soft active devices

Thiol-acrylate based vitrimers combine the advantages of dynamic covalent bonds with the salient features of “click” chemistry including low shrinkage stress and homogenous network properties. The poor storage stability of thiol-acrylate formulations can be overcome by adding an acidic organic phosphate as stabilizer, which at the same time acts as an efficient catalyst to induce transesterifications at elevated temperature. At a sufficiently high rate, the dynamic bond exchange reactions lead to topological rearrangements and a related macroscopic reflow of the photopolymer network. This paves the way towards dynamic photopolymers, which are thermally mendable, malleable, reprocessable and have shape memory properties. In this work, a library of thiol-acrylate monomers for the preparation of digital light processable (DLP) vitrimers is systematically studied. In particular, thiol crosslinkers with varying functionality and number of ester moieties are employed and combined with selected mono- and bi-functional acrylates bearing free –OH groups. In addition, vitrimer networks with higher crosslink density are prepared by adding tri- and tetra-functional acrylates to the formulations. In a comprehensive way, the effect of crosslinking density, monomer structure, network architecture and thermal annealing on cure kinetics, mechanical, thermal and vitrimeric properties of the dynamic photopolymers are studied. The results reveal that by appropriate network design, thermal and mechanical properties of the networks can be controlled over a wide range. In particular, a high mobility of the polymer chains together with a high number of –OH and ester groups is beneficial for inducing fast exchange reactions. The proposed thiol-acrylate based vitrimers show a great potential for the personalized fabrication of soft active devices and their applicability in DLP 3D-printed soft actuators with adequate stretchability and thermal mendability is highlighted.

Calcium-oxidative stress signaling axis and casein kinase 1α mediate eryptosis and hemolysis elicited by novel p53 agonist inauhzin

Inauhzin (INZ) is a novel p53 agonist with antitumor activity. Anemia is a common side effect of chemotherapy and may arise from red blood cell (RBC) hemolysis or eryptosis. In this study, we investigate the mechanisms of INZ toxicity in human RBCs. RBCs were isolated from healthy donors and treated with antitumor concentrations of INZ (5–500 μM) for 24 h at 37 °C. Hemoglobin was photometrically measured, and cells were stained with Annexin-V-FITC for phosphatidylserine (PS), Fluo4/AM for calcium, and 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFDA) for oxidative stress. INZ caused significant dose-responsive, calcium-dependent hemolysis starting at 40 μM. Furthermore, INZ significantly increased Annexin-positive cells and Fluo4 and DCF fluorescence. The cytotoxicity of INZ was also significantly mitigated in presence of D4476. INZ possesses hemolytic and eryptotic potential characterized by cell membrane scrambling, intracellular calcium overload, cell shrinkage, and oxidative stress secondary to calcium influx from the extracellular space.

Synthesis of allyl sulfones bearing urethane groups as efficient addition-fragmentation chain transfer agents for the development of low-shrinkage composites

Polymerization shrinkage represents one of the major drawbacks of dental composites. The incorporation of chain transfer agents into dental formulations is an efficient technology that enables a strong reduction of the shrinkage stress. In this contribution, the synthesis of four new addition-fragmentation chain transfer (AFCT) agents bearing urethane groups is described. These compounds were easily synthesized in three steps. Real-time (RT)-NIR photorheology measurements were performed to evaluate rheological behavior (i.e. time of gelation) and chemical conversion (i.e. double bond conversion at the gel point, final double bond conversion) of dimethacrylate resins containing the synthesized transfer agents. Composites based on these AFCT agents provide good mechanical properties as well as low shrinkage force. The presence of the urethane group results in a significant improvement of the mechanical properties. The addition of urethane AFCT agents to dental composites is an efficient technology that enables the formulation of low shrinkage materials having high flexural strength and modulus.

Interlayer interference during coalbed methane coproduction in multilayer superimposed gas-bearing system by 3D monitoring of reservoir pressure: An experimental study

Coproduction is an important measure for improving coalbed methane flow and production efficiency in multilayer superimposed gas-bearing systems. By monitoring the reservoir pressure in 3D spaces, we analyzed the mechanism of fluid migration and interlayer interference during coproduction through a four-layer coproduction experiment with a reservoir pressure gradient of 0.4 MPa. The results revealed the coupling between reservoir pressure gradient, matrix shrinkage, and effective stress, along with their joint effect on the reservoir pressure evolution in stages. The increase in reservoir pressure or reverse gas flow in low-pressure coal seams is the direct manifestation of interlayer interference. This interference increases gradually as the difference between the pressure gradients of the reservoirs increases. The gas elastic energy was modeled considering the free and adsorption states. We found that the difference in gas elastic energies between reservoirs is a major cause of interlayer interference. The wellbore connects coal seams with different reservoir pressures, that is, it connects different energy bodies. This destroys the state of dynamic energy balance between the systems, causing fluid flow from high-energy gas-bearing systems to those with low energy to achieve a new dynamic balance. When the reservoir energy difference is significant, the fluid in higher energy systems shields or inhibits the fluid flow to the wellbore in lower energy systems and may even cause “backflow” to lower energy systems.

Exogenous healing in concrete with pH-sustained internal carbonation

In this study, experimental investigations were conducted on enhancing the crack-healing potential of concrete using the internal carbonation process. The objective is to overcome one major limitation of autogenous healing (limited carbonation) by using Sodium Carbonate (Na2CO3) solution as a healing agent. To replicate the different types of damages and internal cracking that could arise during the service life of concrete structures, the effects of drying shrinkage and mechanical stresses on the crack-healing proclivity of cement-based materials were explored. A novel technique to measure crack-healing under constantly applied stress is also introduced for better assessment of healing in real-world situations. Results show a significant improvement in healing by using 0.95 M Na2CO3 solution over plain water. Moreover, permeability observations under stress revealed that the potential for healing by the proposed mechanism is strongly dependant on the stress level in samples. In the later part of the paper, Service Life Predictions were also undertaken by utilizing chloride ion diffusion coefficients extracted from the measured permeability coefficients and service life models available in the literature. Results from comparison of predicted service life indicate that at least in qualitative terms, healing with internal carbonation using the Na2CO3 solution led to an increase in the service life of concrete composites.

Formation Features of Electric Conductive Networks in the ABS/MCNT Composite when Manufacturing Filament for FDM-Printing

In this paper, we study the physicomechanical and electrophysical properties of filaments of a nanocomposite made of a copolymer of acrylonitrile with butadiene and styrene (ABS)/multi-walled carbon nanotubes (MCNTs) for FDM-printing (Fusing Deposition Modeling). Both native (TMN) and functionalized (TMF) multiwalled carbon nanotubes were used as fillers. The strength of the filament is shown to depend nonlinearly on the MCNT concentration. The strength initially decreases by 24–34%, and then, as the concentration increases, at 5 wt % of filler increases to values that are 3–5% less than that of unmodified ABS. The filament resistivity reaches 1.1 × 103 and 7.2 × 104 Ω m for TMN and TMF, respectively (the filler concentration is 5 wt %). The power-law dependence of the resistivity on the nanofiller concentration was found to be violated, which is possibly related to segregation of phases with different conductivity in the nanocomposite. The maximum value of the resistivity occurs at a concentration of 2.5 wt % ТМН when the phase with higher conductivity does not yet form a single network, but represents “islands” separated from each other by areas with lower conductivity. Violations of the power-law dependence disappear in the case of saturation of the filament with TMN with water or using TMF as a nanofiller. Changes in the morphology and microstructure of the filament surface were studied by electron microscopy. An increase in the MCNT concentration is shown to lead to a “smoothing” of the surface and may be associated with a deeper relaxation of the shrinkage stresses compressing the filament. The effect manifests itself at minimal TMN concentrations. When using TMP, “smoothing” of the surface is observed at a maximum concentration of 5 wt %. It is shown that the physicomechanical and electrically conductive properties of filaments are determined by the processes of separation of the phases with different conductivity and shrinkage that occur simultaneously during filament production.

Analysis of liquation and solidification cracks in the electron beam welding of GTD-111 nickel-base superalloy joint

The weldability of GTD-111 superalloy by electron beam welding was studied, and the cracking evolution of solidification and liquation, as well as microstructural characteristics, were also investigated. The weld metal microstructure consisted mainly of the inter-dendritic phases of MC, γ-γ′ and γ′ nanoparticles, primarily responsible for the solidification crack in the weld metal. In addition to solidification cracks, the formation of liquation cracks in HAZ was an important challenge with electron beam welding. It was found that M5B3, γ-γ′, MC and γ′ phases leave formation during the increase of non-equilibrium temperature in HAZ, with the formation of partial liquation in the phase-matrix interface and absorption of shrinkage stresses due to welding cooling. Both solidification and liquation cracks decreased as the heat input increased due to the increase in beam current. This was attributed to the reduction of cooling stress and the increase of backfilling capacity.

Shrinkage Stress and Temperature Variation in Resin Composites Cured via Different Photoactivation Methods: Insights for Standardisation of the Photopolymerisation.

The literature has shown that there is no consensus regarding the best resin composite photoactivation protocol. This study evaluated the efficiency of the conventional, soft-start, pulse-delay and exponential protocols for photoactivation of resin composites in reducing the shrinkage stress and temperature variation during the photopolymerisation. The photoactivation processes were performed using a photocuring unit and a smartphone app developed to control the irradiance according each photoactivation protocol. These photoactivation methods were evaluated applying photoactivation energies recommended by the resins manufactures. Three brands of resin composites were analysed: Z-250, Charisma and Ultrafill. The cure effectiveness was evaluated through depth of cure experiments. All results were statistically evaluated using one-way and multi-factor analysis of variance (ANOVA). The use of exponential and pulse-delay methods resulted in a significant reduction of the shrinkage stress for all evaluated resins; however, the pulse-delay method required too long a photoactivation time. The increases on the temperature were lower when the exponential photoactivation was applied; however, the temperature variation for all photoactivation protocols was not enough to cause damage in the restoration area. The evaluation of the depth of cure showed that all photoactivation protocols resulted in cured resins with equivalent hardness, indicating that the choice of an alternative photoactivation protocol did not harm the polymerisation. In this way, the results showed the exponential protocol as the best photoactivation technique for practical applications.

Influence of Cement Thickness on the Polymerization Shrinkage Stress of Adhesively Cemented Composite Inlays: Photoelastic and Finite Element Analysis

The objective of this study was to analyze the effect of cement thickness on the strain and stresses resulting from the polymerization of resin cement using photoelasticity and Finite Element Analysis (FEA). For this study, twenty upper first premolars with inlay cavity preparation were constructed from photoelastic resin and restored with composite resin inlay. The samples were divided into two groups (n = 10) according to the film thickness of resin cement material. For Group 1, the film thickness was 100 μm; for Group 2, the film thickness was 400 μm. After polymerization of the cement, photoelastic analysis and finite element analysis (FEA) were performed. In the photoelastic analysis, Group 2 showed higher strain with the presence of second-order fringe even after 24 h. In Group 1, the formation of first order fringes was not observed, even after 24 h. In the FEA analysis, the greatest cusp deflection and tensile stress occurred in Group 2 (0.00026 mm and 0.305 MPa, respectively) due to the polymerization shrinkage in the lingual cusp compared to Group 1 (0.000107 mm and 0.210 MPa, respectively). It can be concluded that the thickness of the resin cement influences the cusp deflection, with the greater thickness of the cement layer, the greater stresses and deformations in the tooth structure occur.

Influence of Polyvinyl Alcohol Powder on the Mechanical Performance and Volume Stability of Sulfoaluminate–Portland Cement Composite

Cement quick repair materials generally have the defects of brittleness and early shrinkage. The modification of composite cement mortar by water-soluble glue powder—polyvinyl alcohol (PVA)—was studied in the condition of settled water cement ratio. At 90 days, the maximum flexural strength of mortar was 15.4 MPa, which was 1.3 times of the group without PVA and there was no strength shrinkage phenomenon. Through the analysis of the porosity, PVA improved the total porosity; high porosity could play a better role of buffering and absorbing the impact stress, effectively improving the toughness of mortar. At 28 days, the maximum impact resistance was 1.72 J/cm2, which was 1.75 times of the group without PVA. In addition, the increased total porosity also greatly absorbed the shrinkage stress at the early stage, and reduced the mortar self-shrinkage. When the PVA content was 1%, the volume self-shrinkage of mortar decreased from the initial 3360 μm·m−1 to 700 μm·m−1. According to the analysis of hydration heat, the addition of PVA effectively reduced the early hydration heat release rate and alleviated the concentrated heat release phenomenon to a certain extent. In this paper, the hydration reaction of composite cement and the action mechanism of PVA in composite cement were studied by means of X-ray diffraction, infrared spectrum and hydration heat analysis.

Formation of Diagonal Gaps as Stress-Relieving Sites: Rethinking the Concept of Increment Splitting in Direct Occlusal Composite Restorations

The split-increment horizontal placement technique is currently used, along with other restorative techniques, in moderate-to-large occlusal cavities for reducing the shrinkage stress generated during light polymerization. Such stress, if released uncontrolled, may cause damage within the composite, tooth or at the adhesive interface. The term “diagonal cut” was used in our original paper published in 2005 to refer to the action of dividing each composite increment into segments prior to light polymerization and was presented in two-dimensional illustration. Besides, we made no mention in the original paper of the term “diagonal gap” as an outcome of such diagonal cutting. We currently recognize the importance of introducing the “diagonal gap” term and the need for shedding some light on its role to help provide a more comprehensive view of the split-increment technique. The purpose of the current paper is to rethink our increment splitting concept used in direct occlusal composite restorations by introducing the term “diagonal gap” as a stress-relieving vertical site and demonstrating it in a three-dimensional illustration for providing a more comprehensive understanding of the split-increment technique. Conclusion: In the current paper, the term “diagonal gap” is introduced to refer to the vertical gap created by diagonal cutting of the horizontal composite increment, before light curing. This gap enables the segmented composite increment to undergo unrestrained shrinkage, where each segment being free from adhesion at the gap site can deform independently from the other segments. The relief of the polymerization shrinkage stress generated during light curing prevents formation of cracks in enamel and/or composite, and debonding of adhesive interfaces. Keywords: deformation; diagonal gap; incremental; occlusal; polymerization shrinkage; posterior composite; segment; split-increment; stress reduction; stress-relieving site

Mechanics Modeling of Residual Stress Considering Effect of Preheating in Laser Powder Bed Fusion

This study aimed at the investigation of the effect of substrate temperature on residual stress in laser powder bed fusion using a physics-based analytical model. In this study, an analytical model is proposed to predict the residual stress through the calculation of preheating affected temperature profile and thermal stress. The effect of preheating is super-positioned with initial temperature in the modeling of temperature profile using a moving heat source approach; the resultant temperature gradient is then employed to predict the thermal stress from a point body load approach. If the thermal stress exceeds the yield strength of the material, then the residual stress under cyclic heating and cooling will be calculated based on the incremental plasticity and kinematic hardening behavior of metal. IN718 is used as a material example to pursue this investigation. To validate the predicted residual stress, experimental measurements are conducted using X-ray diffraction on IN718 samples manufactured via laser powder bed fusion under different process conditions. Results showed that preheating of the substrate could reduce the residual stress in an additively manufactured part due to the reduction in temperature gradient and resultant shrinkage stresses. However, the excessive preheating could have an opposite impact on residual stress accumulation. Moreover, the results confirm that the proposed model is a valuable tool for the prediction of residual stress, eliminating the costly experiments and time-consuming finite element simulations.

THE COMPARISON OF RESIN-BASED COMPOSITES PHYSICAL PROPERTIES BETWEEN BULK-FILL TECHNIQUE AND INCREMENTAL TECHNIQUE

ABSTRACT:Composite resins are currently the most popular restorative material in dentistry. This is due to good aesthetics and maximum conservation ability. Behind these advantages, there are disbenefits of composite resin materials, such as polymerization shrinkage, which can lead to restoration failure. Various attempts have been investigated to reduce the shrinkage incidence of composite resins, one of which is the technique of placing the restorative material into the cavity. The restoration filling technique is recognized as a significant factor in shrinkage stress. By using a special filling technique, the polymerization shrinkage damage stress can be reduced. There are several techniques in performing composite resin fillings, including bulk and incremental techniques. These techniques have their respective advantages and disadvantages. The aim of this literature review was to compare the physical properties of composite resin restorations with bulk filling and incremental techniques. Physical properties that being studied include polymerization shrinkage, stress shrinkage, degree of conversion, bonding strength, water resorption, color stability, and temperature increase. Comparing the two techniques, composite resin with incremental filling technique has superior physical properties compared to bulk technique. From the comparison of the two techniques, the composite resin with incremental filling technique has superior physical properties compared to the bulk technique, especially in higher conversion which causes lower shrinkage stress. This situation makes the incremental technique provide better bond strength, water resorption, color stability, and lower temperature rise.Keywords: Bulk, Composite Resin, Incremental, Physical Properties, Restoration, Restoration Technique

Computer Aided Design Modelling and Finite Element Analysis of Premolar Proximal Cavities Restored with Resin Composites.

This study evaluated the stress distribution in five different class II cavities of premolar models restored with conventional or bulk-fill flowable composite by means of finite element analysis (FEA) under shrinkage and occlusal loading. An upper validated premolar model was imported in the software, and five class II cavities with different occlusal extensions and dimensions were prepared: horizontal cavity on the mesial surface (horizontal slot), mesio-occlusal cavity, mesial cavity (vertical slot), tunnel type cavity and direct access cavity. The models were restored with conventional or bulk-fill flowable resin composite. The tested materials were considered as homogeneous, linear, and isotropic. The Maximum Principal Stress criteria was chosen to evaluate the tensile stress results. The lowest shrinkage stress value was observed in the direct access cavity restored with bulk-fill flowable resin composite (36.12 MPa). The same cavity, restored with conventional composite showed a score of 36.14 MPa. The horizontal slot cavity with bulk-fill flowable showed a score of 46.71 MPa. The mesio-occlusal cavity with bulk-fill flowable had a score of 53.10 MPa, while with conventional composite this was 55.35 MPa. Higher shrinkage stress was found in the vertical slot cavity with conventional resin 56.14 MPa, followed by the same cavity with bulk-fill flowable 56.08 MPa. Results indicated that the use of bulk-fill flowable composite resin more significantly decreased the polymerization shrinkage stress magnitude. The larger the cavity and the volume of material necessary to restore the tooth, the greater the residual stress on enamel and dentin tissue.

Evaluation of Physical-Mechanical properties of different Bulk-Fill composites / Avaliação das propriedades Físico-Mecânicas de diferentes compósitos Bulk-Fill

The aim of the study was to assess the degree of conversion (DC), microhardness, polymerization shrinkage stress (PSS) and volumetric contraction of two bulk-fill composites (SonicFill, Kerr Corporation, Orange, CA, USA - (SF) and Filtek BulkFill, 3M ESPE, St Paul, MN, USA - (FB)) and one conventional nanofiller resin composite (Z350XT – 3M ESPE, St Paul, MN, USA) inserted incrementally (Z350I) or in bulk (Z350B). Micro-Raman spectroscopy, Knoop microhardness, PSS test and micro-computed tomography technique (?CT) were used to evaluate the resin composites. Data were analyzed with one-way ANOVA followed by Tukey’s post hoc test (? = 0.05). DC was not affected by the type of the composite, excepted when conventional resin composite was inserted in a single increment (p = 0.002). FB and Z350I showed higher microhardness values than Z350B (p = 0,003), while SF showed no statistically significant difference to the other resin composites. No statistical differences were found among the composites regarding to PSS (p = 0.104) and volumetric shrinkage (p = 0.258). Therefore, it can be concluded that bulk-fill and conventional resin composites tested present similar properties. Thus, shorter time required for the use associated with simplified operative technique are considered clinical advantages of bulk-fill composites.

Numerical Simulation of Particle Size Influence on the Sintering Behavior of 316L Stainless Steel Powders Fabricated by Binder Jet 3D Printing

Binder jet 3D printing (BJ3DP) is one of the most promising 3D printing technologies, due to its ability of printing large-scale complex parts with high efficiency and low cost. The powder particle size is crucial for the sintering quality of BJ3DP. In this work, on the basis of the constitutive model of viscoplastic theory, the shape evolution (shrinkage and relative density) of cubes produced by BJ3DP using 316L stainless steel powders (normal distribution of powder sizes) with different mean particle sizes (i.e., 20, 30, 40, 50, 60, and 70 μm) was studied via finite element numerical simulation during sintering. It revealed that the volumetric shrinkage, relative density, and maximum sintering stress decreased with increasing the mean particle size. The maximum sintering stress of the sample with mean particle size of 70 μm was 0.0492 MPa, with the volumetric shrinkage of ~40% and the relative density of ~89%. In the meantime, the maximum sintering stress of the sample with mean particle size of 20 μm was 0.1789 MPa, with the volumetric shrinkage of ~48% and the relative density of ~97%. In addition, the simulated results of the relative density of assumed samples agreed well with the experimental results from the literature.

Global Sensitivity Analysis of Parameters During Cure Process of SRM Composite Case

The case for modern solid rocket motor (SRM) is a complex compose structure with fiber reinforced resin matrix composite, insulation layer and metal connections, the case forming process is a multi-physical–chemical process which involving heat transfer, chemical reaction and structure deformation. During the cure process, temperature determines whether the case cure completely and the uniformity of temperature field is an important factor in causing residual thermal stress and shrinkage stress, so temperature field is the key to the mutual coupling effect of each physical and chemical process, and the basis to analyze the cure process of the case. During the cure process of case, fluctuation of cure temperature, cure time or heat transfer of hot air in the furnace may occur, which make the actual forming process of case deviate from the ideal cure process. In order to investigate the sensitive degree of thermal cycle, convective heat transfer coefficient and thermal properties to cure uniformity during cure process of composite case, the influence rule of the three factors on uniformity of temperature and cure degree fields were analyzed by numerical simulation. A thermal-chemical model was built for a simplified composite SRM case firstly, and the model was verified. Then, the influence degree of the three factors on cure uniformity of composite case was analyzed and quantized by the Morris global sensitivity analysis method. The results show that he sensitivity order of the uniformity of temperature field for the four parameters is: thermal diffusion coefficient > heat transfer coefficient > duration time > cure temperature. Besides, he temperature and duration time of the fourth dwell stage have less effect on the cure uniformity of composite case than that of heat transfer coefficient. Therefore, it is a challenge to design a thermal cycle that can not only guarantee the vulcanization of EPDM insulation layer, but also improve the cure uniformity.

Development of a difunctional oxirane and multifunctional acrylate interpenetrating polymer network composite system with antimicrobial properties

AbstractThis research continued the development of a difunctional Oxirane and multifunctional Acrylate interpenetrating polymer network composite System (OASys) with antimicrobial properties. The effects of 4‐Isopropyl‐4′‐methyldiphenyliodonium tetrakis (pentafluorophenyl) borate (Borate), hexamethylene diamine (HMDA) and N,N‐dimethyl p‐toluidine (DMPT) on OASys (Epalloy 5001:dipentaerythritol hexaacrylate) composite hardness, contact angle, monomer‐to‐polymer degree of conversion (DoC), mechanical properties, polymerization shrinkage, shrinkage stress, and antimicrobial properties were determined. Bis‐GMA:TEGDMA composites were used as the control. OASys composites with 9 wt% Borate and 0.5 wt% DMPT or 1.5 wt% HMDA had comparable hardness, DoC's and polymerization shrinkages to controls, but had lower contact angles and mechanical properties. Additionally, OASys composites with 1.5 wt% HMDA had significantly less polymerization stress than controls and demonstrated significant antibacterial activity against Streptococcus mutans and Lactobacillus casei out to 3 months. With lower shrinkage stress and long‐term antimicrobial activity, OASys composites look promising for increasing the clinical lifetime of dental composites, but improvements in mechanical properties are needed.