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Fast-curing halogen-free flame-retardant epoxy resins and their application in glass fiber-reinforced composites
摘要： A series of novel fast-curing halogen-free flame-retardant epoxy resins were formulated and used to prepare glass fiber-reinforced composites. Dynamic mechanical analysis showed that the optimized epoxy system could be completely cured in 0.5 h at 150°C and had a glass transition temperature (Tg) of above 130°C. The optimized epoxy system was also used as matrix resin to make glass fiber prepregs and composite panels. The flame-retardant properties of the glass fiber-reinforced composites were investigated, including the limiting oxygen index (LOI) and flaming, smoke and toxicity properties. The glass fiber-reinforced composite had good flame retardancy with a UL-94 V-1 rating and high LOI of ≥36%. More significantly, the composite based on the flame-retardant epoxy resin showed lower smoke density compared with those based on phenolic resins. Finally, the glass fiber prepregs were used to fabricate honeycomb sandwich composites. The peel strength of the epoxy-based composites was almost twice that of the composites based on phenolic resin.
关键词： prepregs,fast cure,glass fiber-reinforced composites,halogen-free flame retardancy,epoxy resins
更新于2025-09-23 15:23:52
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Reporting of light irradiation conditions in 300 laboratory studies of resin-composites
摘要： Objective. To evaluate how the light delivered to resin-composites was described in recent articles. Method. PubMed was searched for 300 articles published between January 2017 and May 2018 with keywords relating to photocuring of dental materials. The articles examined a wide range of resin-composite properties and performance. For each article, the information provided about the light curing unit (LCU), the light curing conditions and the characteristics and quantity of the light used in the study were recorded. Specifically, the type of LCU used; the irradiance; how the irradiance was measured; the exposure times; whether the light energy (radiant exposure) received by the specimen was determined, or if only the light output at the LCU tip was measured; whether the distance between the tip of the LCU and the specimen was reported; and whether the emission spectrum from the LCU was reported. Where possible, the resin manufacturer’s minimum energy requirement (MER: the product of the recommended minimum exposure time and irradiance) was compared to the radiant exposure delivered to the specimen. Results. Of the 300 articles examined, 217 were published in 2017 and 83 in 2018. Of these articles, 130 (43%) were found in open access journals, and 170 (57%) were in subscription-based journals. The name of the LCU used was not provided in 31 articles, 14 articles did not provide the exposure time, and 227 articles did not report the distance to the specimen. An irradiance value was reported in 231 articles, but this was the irradiance received by the specimen in only 48 instances. The emission spectrum from the LCU was reported in 15 articles. There was a large range in the radiant exposures from below 10 J/cm2 to greater than 100 J/cm2. Significance. The majority of articles from 2017 and early 2018 did not include sufficient description of the characteristics and quantity of the light received by the resin-composite specimens to allow the study to be replicated. It is recommended that future articles should report: (1) the identity of the LCU used; (2) the radiant exposure received by the specimen (J/cm2); and (3) appropriate reference to the emission spectrum from the LCU.
关键词： Research reproducibility and replicability,Bond strength,Resins,Light curing,Bulk fill,Light measurement
更新于2025-09-23 15:23:52
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Synthesis of Cyanate Esters Based on Mono-O-Methylated Bisphenols with Sulfur-Containing Bridges
摘要： We described a synthetic approach to bisphenol-based monocyanate esters based on mono-O-methylation of parental bisphenols followed by cyanation of the residual phenolic hydroxyl. Structures of the synthesized compounds were determined by the application of IR, NMR 1H and 13C spectroscopies, EI and MALDI mass spectrometry, and purity of the final product was controlled by HPLC. We showed that stability of the cyanate esters depends on the nature of the bridging group. Temperature range of thermally initiated cyclotrimerization of synthesized monocyanate ester, as well as reaction enthalpy, was determined by differential scanning calorimetry (DSC).
关键词： cyanate resins,bisphenols,curing,Mitsunobu reaction,aryl cyanates,cyanate esters,thermal analysis
更新于2025-09-23 15:22:29
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Materials containing benzocyclobutene units with low dielectric constant and good thermostability prepared from star-shaped molecules
摘要： With the development of ultralarge-scale integrated circuits, polymers with low dielectric constant and high thermal stability have aroused great interest. We prepared two novel bridged siloxane-based benzocyclobutene (BCB) star-shaped monomers, tetrakis[dimethyl siloxy-4-(10,10-dimethyl-10-ethyl silicon)-benzocyclobutene] (TDSDES-BCB) and tetrakis(hexamethyl siloxane vinyl-benzocyclobutene) (THSV-BCB), and the corresponding resins were obtained by curing. The structures of TDSDES-BCB and THSV-BCB were confirmed by 1H-NMR, 13C-NMR, and 29Si-NMR spectra and time-of-flight mass spectrometry analysis. The curing behavior of these monomers was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry. The dielectric constant of cured TDSDES-BCB is only 2.43 at 10 MHz (that of THSV-BCB is 2.46). In addition, these resins display high thermal stability: the 5 wt % weight loss temperature of cured TDSDES-BCB is about 467 °C (454 °C for THSV-BCB resin). The excellent low dielectric property is attributable to the free volume created by the star-shaped structure and crosslinked network structure of BCB after curing.
关键词： thermosets,structure–property relationships,resins,dielectric properties,thermal properties
更新于2025-09-23 15:22:29
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High-Performance Biobased Unsaturated Polyester Nanocomposites with Very Low Loadings of Graphene
摘要： Graphene-reinforced tung oil (TO)-based unsaturated polyester nanocomposites were prepared via in situ melt polycondensation intergrated with Diels–Alder addition. Functionalized graphene sheets derived from graphene oxide (GO) were then extracted from the obtained nanocomposites and carefully characterized. Furthermore, dispersion state of the graphene nanosheets in the cured polymer composites and ultimate properties of the resultant biobased nanocomposites were investigated. Mechanical and thermal properties of the TO-based unsaturated polyester resin (UPR) were greatly improved by the incorporation of GO. For example, at the optimal GO content (only 0.10 wt %), the obtained biobased nanocomposite showed tensile strength and modulus of 43.2 MPa and 2.62 GPa, and Tg of 105.2 ?C, which were 159%, 191%, and 49.4% higher than those of the unreinforced UPR/TO resin, respectively. Compared to neat UPR, the biobased UPR nanocomposite with 0.1 wt % of GO even demonstrated superior comprehensive properties (comparable stiffness and Tg, while better toughness and thermal stability). Therefore, the developed biobased UPR nanocomposites are very promising to be applied in structural plastics.
关键词： unsaturated polyester resins,graphene,in situ melt polycondensation,tung oil,biobased polymer nanocomposites
更新于2025-09-23 15:21:21
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Evaluation of marginal and internal fit of acrylic bridges using optical coherence tomography
摘要： Background: The potential of non-invasive optical coherence tomography (OCT) as a tool for assessment of fit of indirect reconstructions is not fully explored. Objectives: The objectives were to investigate the feasibility and validity of OCT, and to measure the internal and marginal fit of acrylic bridges fabricated using direct and indirect digitalization. Methods: The accuracy of the employed swept source OCT (wavelength: 1310nm) was assessed by comparing with an object with known dimensions. Validity was assessed by comparing OCT measurements on replica, mimicking the cement film thickness, with stereomicroscopic measurements. The reconstructions were placed on the abutments without cementation. The internal and marginal fit of acrylic bridges from direct and indirect digitalization techniques were then assessed by obtaining 5 OCT B-scans per abutment tooth at pre-defined positions located 250 μm apart. The marginal and internal cement gaps were measured using image-processing software (ImageJ). Mean and standard deviation were calculated for both groups and t-test assuming unequal variances was carried out. The level of significance was defined at 0.05. Results: A strong linear correlation (r = 0.865) between OCT and stereomicroscopy was found. T-test showed significantly (P < 0.01) better internal fit of bridges made from indirect digitalization, but no difference in marginal fit. Conclusion: OCT is a feasible and valid tool for investigating internal and marginal fit of acrylic dental reconstructions. Better internal fit was observed in bridges fabricated using the direct digitalization technique. No difference in marginal fit was found between the two fabrication methods.
关键词： Accuracy,Dental marginal fit,Replica technique,Optical coherence tomography,Dental internal fit,Acrylic Resins
更新于2025-09-23 15:21:01
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Flow Behaviors of Polymer Colloids and Curing Resins Affect Pore Diameters and Heights of Periodic Porous Polymer Films to Direct Their Surface and Optical Characteristics
摘要： Manipulation of both pore diameters and heights of two-dimensional periodic porous polymer films is important to extensively control their characteristics. However, except for using different sized colloid templates in replication methods, effective method that tunes these factors has rarely been reported. We find both parameters are controllable by adjusting the flow behaviors of polystyrene colloids and curing resin precursors while preparing phenolic resin and polydimethylsiloxane periodic porous films by embedding their precursors into colloidal crystal monolayers. We adjust the flow behaviors by either varying film preparation temperatures (≥ glass transition temperature of polystyrene) or using the precursors mixed with different amounts of a solvent that renders the colloids viscous. Consequently, the pore diameters and film heights change by 36–56% and 56–84%, respectively. Such modulation results in the change in height to dimeter ratios and the areal fractions of resins at air-film interfaces, thereby significantly changing the water contact angles on these surfaces and their photonic characteristics. This straightforward method does not require additional steps, differently sized colloids, or different amounts of precursors for these parameter controls.
关键词： polymer colloids,Periodic porous polymer films,flow behaviors,curing resins,simultaneous height and pore controls,replication method
更新于2025-09-19 17:15:36
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Avalia??o do grau de convers?o de resinas compostas fotoativadas em diferentes tempos e potências
摘要： Introduction: Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of composite resins. Objective: To evaluate the degree of conversion (DC) and hardness of composite resins photoactivated in different power densities and curing times. Materials and method: Eighty (n=80) composite resin specimens (FiltekTM Z350 XT color A2B) with 4 mm of diameter and 2 mm of thickness were produced, whereas forty (n=40) were meant for the evaluation of degree of conversion and forty (n=40) for hardness. Ten (n=10) specimens were produced for each group assessed, whereas five were meant for the evaluation of the degree of conversion and five for hardness (P10T2; P7T2; P4T2; P1T2; P10T4; P7T4; P4T4; P1T4). Resins of the degree of conversion and hardness were photoactivated by LED for 20 seconds at power intensities of 1000 mW/cm2, 700 mW/cm2, 400 mW/cm2, and 100 mW/cm2, for groups P10T2, P7T2, P4T2, and P1T2, respectively. Groups P10T4, P7T4, P4T4, and P1T4 were cured in the same power intensity, but for 40 seconds. Result: Regarding the degree of conversion, P1T2 resins had the lowest mean value of 22.67 %, and P10T4 resins had the highest mean value of 87.9%. As for hardness, P1T2 resins also had the lowest mean of 30.93 kgf/mm2, and P10T4 had the highest mean of 82.02 kgf/mm2. Conclusion: The higher the power of the curing unit, the higher the DC and hardness of composites resins. The results of this study suggest that a device with intensity of 100 mW/cm2 does not provide satisfactory degree of conversion and hardness, compromising the performance of the restorative material.
关键词： Composite resins,Hardness,Polymerization
更新于2025-09-19 17:15:36
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Four-year clinical prospective follow-up of resin composite restoration after selective caries removal using Er:YAG laser
摘要： Objectives The aim of this study was to longitudinally evaluate, after a 4-year period, the clinical longevity of composite resin restoration compared to the baseline, after selective caries removal in permanent molars using Er:YAG laser or bur preparation with biomodification of dentin with the use of chlorhexidine. Methods Selective caries removal was performed on 80 teeth of 20 individuals who each had at least four active carious lesions. These lesions, located on occlusal surfaces of permanent molar counterparts, were removed using (i) Er:YAG laser biomodified with chlorhexidine, (ii) Er:YAG laser and application of deionized water, (iii) bur preparation biomodified with chlorhexidine, and (iv) bur preparation and application of deionized water. At the end of 4 years, 64 of the 80 restorations were evaluated in 16 individuals (n = 16). The restorations were evaluated, both clinically and photographically, using scanning electron microscopy (SEM) and pulp vitality analysis. The experimental data were statistically evaluated by kappa, Fisher’s, and chi-square tests, with a significance level of 5%. The Kaplan–Meier test and the Cox regression analysis were used to evaluate the survival of the restorations. Results After 4 years of follow-up, there was a statistically significant difference in marginal discoloration criteria for all of the groups evaluated. For marginal adaptation criteria, there was a statistically significant difference for the Er:YAG laser group biomodified with chlorhexine (p = 0.050). For clinical and radiographic evaluation of pulp vitality, there were no statistically significant differences among the groups (p = 0.806). Conclusion Er:YAG laser can be used for selective caries removal, regardless of dentin biomodification with chlorhexidine or application of deionized water, once it produced promising results in composite resin restorations after 4 years of follow-up, according to the criteria evaluated. The selective caries removal using Er:YAG laser or bur and influence the survival of composite resin the biomodification of dentin with the use of chlorhexidine did not restorations after the 4-year follow-up period. Clinical relevance Composite resin restorations applied after selective caries removal using Er:YAG laser or burs, regardless of dentin biomodification with the use of chlorhexidine or application of deionized water, showed adequate clinical behavior after 4 years of follow-up.
关键词： Clinical trial,Dental marginal adaptation,Permanent restorative dentistry,Lasers,Composite resins
更新于2025-09-12 10:27:22
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Citric Acid Capped CdS Quantum Dots for Fluorescence Detection of Copper Ions (II) in Aqueous Solution
摘要： Four kinds of hypercrosslinked resins (acidic resins labeled SAMR and TAMR and heterocyclic resins IDLMR and PRLMR) were synthesized as adsorbents to remove m-phenylenediamine (MPD) from aqueous solution comparably. The Brunauer–Emmett–Teller speci?c surface area and pore size distribution of the two types of resins have been compared, and the infrared spectra of the resins con?rm the presence of the modi?ed groups. The adsorption isotherms illustrate that the Freundlich equation ?ts more appropriately than the Langmuir equation or the Temkin equation. In addition, the kinetic curves indicate that the pseudo-second-order model is a better ?t than the pseudo-?rst-order model. The thermodynamic studies show that the isosteric adsorption enthalpy changes (ΔH) and the Gibbs free energy change (ΔG) are both negative, revealing that all of the adsorption processes are spontaneous and exothermic. All of the modi?ed resins exhibit the best adsorption capacity at pH = 6.24. The results show that the acidic resins have better adsorption of MPD. ? 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47378.
关键词： kinetics,resins,adsorption
更新于2025-09-11 14:15:04