Double Bond Conversion Research Articles

Synthesis and characterization of polyurethane acrylate with bio-oil modification for photo-curing 3D printed flexible structures

The use of renewable resources for additive manufacturing has grown significantly as a means of advancing the ongoing shift to a green economy. This study uses bio-oil generated from the rapid pyrolysis of forest waste as a bio-based chemical to partially replace polyethylene glycol to synthesize a new type of bio-oil modified polyurethane acrylate, used in photo-curing 3D printing technology. The study explores the impact of the ratio of bio-oil to polyethylene glycol on the properties of polyurethane resin. As the amount of bio-oil added increases, the molecular weight of polyurethane acrylate decreases. Modified photosensitive resin showcases better suitability for photo-curing 3D printing, with lower viscosity and volume shrinkage, and its printed samples exhibit enhanced mechanical strength and improved thermal stability. In particular, when the bio-oil substitution rate is 20 wt%, the tensile strength of the 3D printed sample increases by 70 %, and the double bond conversion rate reaches 58.07 %. Meanwhile, the hollow and branching structures of 3D printing have the characteristics of high precision and flexibility. Introducing bio-oil into 3D printing technology not only expands the application fields of bio-oil but also provides new considerations for the transition of photosensitive resins from petroleum-based to renewable fields.

A low mobility UV-LED benzophenone photoinitiator

With the increase frequency of food safety incidents caused by migrating photoinitiators over the past few years, as well as people’s growing awareness of safety and environmental protection, the development of low-migration UV-LED photoinitiators has become increasingly crucial. A photoinitiator 3-vinyl-4-dimethylaminobenzophenone (NVBP) with both hydrogen donor and polymerizable double bond group was prepared and characterized by 1H NMR and 13C NMR. A systematic study of the photopolymerization kinetics of NVBP was explored by the Real-Time Fourier Transform Infrared Spectrometer. The results showed a good initiation efficiency of acrylate monomers under 365 nm/405 nm light source with double bond conversion up to 94.6 % and 79.7 %. In addition, NVBP has low mobility, which is important to facilitate photoinitiator applications. This work proves that NVBP is an excellent UV-LED photoinitiator.

The role of the Terminal Benzene Derivatives in Triphenylamine‐Based Oxime Esters for Free Radical Photopolymerization

AbstractIn this study, we investigate the effect of terminal benzene derivatives in triphenylamine‐based oxime esters on their photoreactivity. Five novel oxime esters (Miko series) that containing different benzene derivatives as terminal groups, were synthesized. The electronic properties of the substituents on the benzene ring range from electron‐donating to electron‐withdrawing. Specifically, a methoxy benzene for Miko‐MOB, tert‐butyl benezene for Miko‐t‐Bu, chloro benzene for Miko‐CB, trifluoromethyl benzene for Miko‐TFM, and nitro benzene for Miko‐NB. Additionally, a compound with benzene only as the terminal substituent (TP‐1) was selected for comparision. All the new compounds exhibited higher molar extinction coefficients than TP‐1. Additionally, the steady‐state photolysis and electron spin resonance (ESR) properties would decrease from the electron‐donating substitutes to electron‐withdrawing substitutes. Finally, these oxime esters are utilized in Type I photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) under UV or LED@405 nm light irradiation conditions. Among all formulations, Miko‐MOB demonstrated the highest double bond conversion efficiency under both UV and LED@405 nm light irradiation. Thus, terminal benzene derivatives in oxime esters play an important role in tuning the optical and photochemical reaction performance, offering significant value for the design strategy of such photoinitiators.

Aluminum zirconate nanoparticles in etch and rinse adhesive to caries affected dentine: An in-vitro scanning electron microscopy, elemental distribution, antibacterial, degree of conversion and micro-tensile bond strength assessment.

To incorporate different concentrations of Al2O9Zr3 (1%, 5%, and 10%) nanoparticles (NP) into the ER adhesive and subsequently assess the impact of this addition on the degree of conversion, μTBS, and antimicrobial efficacy. The current research involved a wide-ranging examination that merged various investigative techniques, including the application of scanning electron microscopy (SEM) for surface characterization of NP coupled with energy-dispersive x-ray spectroscopy (EDX), Fourier-transform infrared (FTIR) spectroscopy, μTBS testing, and microbial analysis. Teeth were divided into four groups based on the application of modified and unmodified three-step ER adhesive primer. Group 1 (0% Al2O9Zr3 NPs) Control, Group 2 (1% Al2O9Zr3 NPs), Group 3 (5% Al2O9Zr3 NPs), and Group 4 (10% Al2O9Zr3 NPs). EDX analysis of Al2O9Zr3 NPs was performed showing elemental distribution in synthesized NPs. Zirconium (Zr), Aluminum (Al), and Oxides (O2). After primer application, an assessment of the survival rate of Streptococcus mutans was completed. The FTIR spectra were analyzed to observe the characteristic peaks indicating the conversion of double bonds, both before and after the curing process, for the adhesive Etch and rinse containing 1,5,10 wt% Al2O9Zr3 NPs. μTBS and failure mode assessment were performed using a Universal Testing Machine (UTM) and stereomicroscope respectively. The μTBS and S.mutans survival rates comparison among different groups was performed using one-way ANOVA and Tukey post hoc (p = .05). Group 4 (10 wt% Al2O9Zr3 NPs + ER adhesive) specimens exhibited the minimum survival of S.mutans (0.11 ± 0.02 CFU/mL). Nonetheless, Group 1 (0 wt% Al2O9Zr3 NPs + ER adhesive) displayed the maximum surviving S.mutans (0.52 ± 0.08 CFU/mL). Moreover, Group 2 (1 wt% Al2O9Zr3 NPs + ER adhesive) (21.22 ± 0.73 MPa) samples displayed highest μTBS. However, the bond strength was weakest in Group 1 (0 wt% Al2O9Zr3 NPs + ER adhesive) (14.13 ± 0.32 MPa) study samples. The etch-and-rinse adhesive exhibited enhanced antibacterial activity and micro-tensile bond strength (μTBS) when 1% Al2O9Zr3 NPs was incorporated, as opposed to the control group. Nevertheless, the incorporation of Al2O9Zr3 NPs led to a decrease in DC. RESEARCH HIGHLIGHTS: 10 wt% Al2O9Zr3 NPs + ER adhesive specimens exhibited the minimum survival of S.mutans. 1 wt% Al2O9Zr3 NPs + ER adhesive samples displayed the most strong composite/CAD bond. The highest DC was observed in Group 1: 0 wt% Al2O9Zr3 NPs + ER adhesive.

Photobleachable coumarin-thioester derivatives with low cytotoxicity as visible-light photoinitiators for free radical and cationic photopolymerization

The development of photoinitiators is suffering from deep color, low solubility, and biotoxicity caused by the introduction of large-conjugated structures, also the complex synthetic procedures constrain the application of photoinitiators. To overcome this issue, nine kinds of coumarin thioester photoinitiators (CTEs) have been delicately designed and synthesized through a simple, metal-free two-step reaction. CTEs with excellent light absorption properties in the visible light range can be used not only as a type I photoinitiator but also as a type II photoinitiator, and sensitizer in the cationic photoinitiating system. CTEs effectively initiate the photopolymerization of tripropylene glycol diacrylate (TPGDA) under the irradiation of 405 nm LED, and the double bond conversions are similar to or better than those of commercial photoinitiators. Also, the cationic photopolymerization of bisphenol A diglycidyl ether (BADGE) is successfully initiated by CTEs/IOD systems. Notably, the epoxy group conversion initiated by 6O-CTE/IOD reaches 72.1 %, surpassing that of the commercial photoinitiating system. The photoinitiating mechanism of CTEs is proposed and supported by theoretical calculations. Furthermore, the bond cleavage abilities of CS bonds endow CTEs with photobleaching properties. The colorless cured film initiated by 6O-CTE was obtained under only 15 s irradiation, indicating their application prospects of CTEs in colorless photopolymerization. More importantly, the cytotoxicity of CTEs is much lower than that of commercial photoinitiator TPO. This work provides new insight into the design of biocompatible photoinitiators with a photobleaching property for LED photopolymerization.

Polyester networks based on Tulipalin A and ε‐caprolactone and activation of the Thioether groups by incorporation of trialkylsulfonium salts

AbstractLinear and star‐shaped poly(ε‐caprolactone‐co‐α‐methylene‐γ‐butyrolactone) P(CL‐co‐MBL) copolyesters with a pendant functional double bond of α‐methylene‐γ‐butyrolactone (MBL) comonomer were used as polymeric precursor for organo‐gels formation. Crosslinking was carried out by light‐initiated thia‐Michael reaction using 1,5‐pentanedithiol (PDT) and pentaerythritol tetrakis(3‐mercaptopropionate) (PETK). Double bond conversion and the content of free thiol groups in the obtained networks was followed and rationally estimated using confocal Raman spectroscopy. The gel content and the crosslinking density varied based on MBL comonomer and crosslinker content and were highest for slight thiol to double bond excess (SH/vinyl; 2/1 molar ratio) while decreasing with further thiol excess. These parameters were more pronounced by the replacement of linear PDT with the star‐shaped PETK crosslinker. The thermal and rheological properties investigation of the obtained materials was performed employing DSC, TGA and using frequency and temperature sweeps rheological measurements. Shear moduli in the range 0.14 up to 0.93 MPa were obtained due to different content of MBL in pre‐polymer and crosslinker in network formation. The strength was caused by the crystalline phase of the PCL segments up to a temperature of 50°C. Formed thioether bond within the network were not reversible up to 150°C as it was found based on temperature sweep rheology. Following, the activation and conversion of thioether bonds within the obtained materials into trialkylsulfonium salts was attained through the alkylation using butyl brosylate. The dynamic nature of the transalkylation at elevated temperature 150°C allowed network rearrangement, which was proved by stress relaxation experiment and investigation of the self‐healing capabilities.

Preheating and "snow-plow" composite application technique affect double bond conversion but not bond strength to dentine.

To measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow-plow technique with/without preheating and temperature in the preheated composite. For DC, snow-plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light-curing composites simultaneously in standardized molds while in control groups light-curing was separate. DC of Flow was measured using micro-Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow-plow) or separate (control) light-curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05). Increased curing time significantly increased DC in snow-plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow-plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow-plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long-term). Temperature in the preheated Bulk dropped to ~38°C after 30 s. Snow-plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light-curing of composite increments. Snow-plow, irrespective of preheating, resulted in similar initial and long-term MTBS to dentine. Clinicians with preference for flowable composite liners in Class II restorations should be aware that the snow-plow technique of simultaneous light-curing of flowable and bulk-fill composite increments affects monomer-to-polymer conversion, albeit no effect on immediate, and long-term bonding to dentine was detected. Preheating sculptable bulk-fill composite improves conversion of the flowable liner in the snow-plow technique but has no detectable effect on bond strength to dentine.

Photopolymerization Pattern of New Methacrylate Cellulose Acetate Derivatives.

Polymeric photocrosslinked networks, of particular interest in the design of materials with targeted characteristics, can be easily prepared by grafting light-sensitive moieties, such as methacrylates, on polymeric chains and, after photochemical reactions, provide materials with multiple applications via photopolymerization. In this work, photopolymerizable urethane-methacrylate sequences were attached to free hydroxyl units of cellulose acetate chains in various proportions (functionalization degree from 5 to 100%) to study the properties of the resulting macromolecules and the influence of the cellulosic material structure on the double bond conversion degree. Additionally, to manipulate the properties of the photocured systems, the methacrylate-functionalized cellulose acetate derivatives were mixed with low molecular weight dimethacrylate derivatives (containing castor oil and polypropylene glycol flexible chains), and the influence of UV-curable composition on the photopolymerization parameters being studied. The achieved data reveal that the addition of dimethacrylate comonomers augmented the polymerization rates and conversion degrees, leading to polymer networks with various microstructures.

POSS hybrid bioactive glass dental composite resin materials: Synthesis and analysis

IntroductionThis study create a dental composite by hybirding polyhedral oligo-sesquioxide nano monomers and bioactive glass BG 45S5. MethodsMake an experimental composite resin material with a 60 % filler content overall by substituting 20 % of the filler with BG 45S5. The experimental resins are grouped and named P0, P2, P4, P6 and P8 based on the reactive nanomonomer methacrylic acid-based multifaceted oligomeric sesquisiloxane (POSS) added by 2 %–8 % in the resin matrix portion of each group. Utilize a universal testing machine to analyze and compare the mechanical properties of these, then perform Fourier infrared spectrum analysis, double bond conversion analysis, and scanning electron microscope analysis. Based on this, after soaking the experimental materials artificial saliva solution or lactic acid solution for a while, the pH changes of the solution, the release of Ca2+ and PO43− ions, and the precipitation of apatite on the resin material's surface were tested and analyzed. Cell viability tests were used to assess sample cell viability and quantify the cytotoxicity of biological cells. The independent sample t-test was used to examine the group comparisons, and a difference was considered statistically significant at P<0.05. ResultsOutstanding mechanical and the double bond conversion are demonstrated by the nanocomposites when the POSS concentration hits 4 wt%. Agglomeration will cause the performance to deteriorate if the concentration beyond this threshold. In the P4 group, the double bond conversion, CS, and FS rose by a large margin, respectively, in comparison to the blank control group P0. Thankfully, the data demonstrate that adding POSS increases adhesive ability when compared to the blank group P0, however, there is no discernible difference between the other experimental groups. The acid neutralization capacity of the P4 group is essentially the same as that of the control group (P0). Ca2+ and PO43− ions are released in significant amounts following treatment with lactic acid solution, although this tendency is clearly less pronounced in artificial saliva. SEM and EDX data indicate that when the experimental resin is soaked in lactic acid solution and artificial saliva, apatite precipitation will happen on its surface. The results of the cell viability test indicated that there was no statistically significant difference between the experimental groups, and the viability of the cells increased after 24hours and 48 hours. ConclusionsPOSS was included into the composite resin along with 20% bioactive glass as a filler. When the proportion of POSS is less than 4%, the indices of composite resin materials rise in a dose-dependent way. When this value is surpassed, performance begins to deteriorate. The inclusion of POSS has no influence on the biological activity of the composites, which means that the hybrid composite resin is capable of acid neutralization, ion release, and apatite precipitation. Clinical SignificanceThe experimental composite resin can be used as an intelligent material in clinical treatment. It has the clinical application potential of preventing demineralization of tooth hard tissue, promoting remineralization, and improving edge sealing through apatite precipitation.

Photopolymer-Based Composite with Substance Release Capability Manufactured Additively with DLP Method.

In this study, caffeine-loaded photoresin composites with homogeneous structures, suitable for additive manufacturing of transdermal microneedle systems, were obtained. The properties of the composites with varying caffeine concentrations (0.1-0.4% w/w) were investigated for carbon-carbon double bond conversion using Fourier Transform Infrared Spectroscopy, surface wettability and mechanical properties using a static tensile test and nanoindentation, and caffeine release in ethanol using UV-Vis. The caffeine concentration did not affect the final degree of double bond conversion, which was confirmed in tensile tests, where the strength and Young's modulus of caffeine-loaded samples had comparable values to control ones. Samples with 0.1 and 0.2% caffeine content showed an increase in nanohardness and reduced elastic modulus of 50 MPa and 1.5 MPa, respectively. The good wettability of the samples with water and the increase in surface energy is a favorable aspect for the dedicated application of the obtained composite materials. The amount of caffeine released into the ethanol solution at 1, 3 and 7 days reached a maximum value of 81%, was higher for the lower concentration of caffeine in the sample and increased over time. The conducted research may enhance the potential application of composite materials obtained through the digital light processing method in additive manufacturing.

Investigation of the size effect of mica sheets on the anticorrosion behavior of UV‐cured coatings

AbstractIn this article, four different grades of mica sheets were used to investigate the influence of the size of mica sheet on the UV‐curing process and the anticorrosion performance of UV‐cured coatings. The dispersion of mica sheets in coating matrix was explored by viscosity and morphology measurements. The curing behavior of the composite coatings was studied by gel content and double bond conversion rate. The dispersing behavior of the mica sheets with different grades was investigated by SEM image and rheology measurement. And the anticorrosive performance of the UV‐cured composite coatings was studied by electrochemical measurements and neutral salt spray tests. It was found that the curing degree of the UV‐cured coating was not affected with incorporation of mica sheet as well as its size. Mica sheets with medium size (10 μm) could be more efficiently dispersed in UV‐cured coating than other grades, which helps to form a denser filler pathway and suppresses the diffusion of corrosive agents into the coating matrix, leading to the lowest water adsorption and best anticorrosion performance. After 45 days of immersion in NaCl solution, the impedance modulus of the UV‐cured composite coating with 10 μm mica sheets did not decrease and still maintained at the initial impedance value. After 1500 h's salt spray test, the corresponding coating remained intact without bubbling, peeling, corrosion, and other defects, whereas the coating with other grades of mica sheets all exhibited corrosion pits and blisters, demonstrating that the size of mica sheet played an important role in enhancing the anticorrosion performance of UV‐cured coatings.

Efficient reduction of photopolymerization shrinkage stress through microporous particles templated from Pickering emulsion droplets

Photopolymerization of acrylate based resin is a rapid, efficient and low-energy curing process that is achieving wide applications in many industrial fields. However, the volumetric shrinkage and the shrinkage stress of the cured resin have long been the major factor reduces adhesion strength of UV curable coatings onto the substrate. In this paper, the Pickering emulsion template method is employed to prepare elastic microporous particles with well-defined surface and internal structures and these microporous particles are thus added into the UV curable resin formulation to verify their capability to reduce polymerization stress through the microporous structure. The gel point time of UV-curable materials is delayed by 11 s with 1.5 wt% addition of the microporous particles and the double bond conversion at the gel point is subsequently increased. By real time MIR-photo-rheology and 3D line scanning laser confocal measurement, it is found that addition of microporous particles into the resin formulation can reduce the volume shrinkage of the resin by 61.2 % with only 1.5 wt% microporous particles, while the excellent mechanical and thermal properties of the cured resin is basically maintained.

Radiation Curing of Phosphorus Telomer-Based Coatings Using UV LEDs or Medium-Pressure Mercury Lamp

In the presented study, UV LEDs (365 nm) or a medium-pressure mercury lamp (UV-ABC) were verified as UV radiation sources initiating the photocrosslinking process of varnishes based on novel photopolymerizable phosphorus (meth)acrylate oligomers. Coating formulations were composed of (meth)acrylic/styrene telomers with terminal P-atoms (prepared via a UV phototelomerization process) and different photoinitiators (HAPs, APOs, or APO blends). The kinetics of the UV crosslinking process of the coating formulations depending on UV irradiation and the UV range was investigated by the photo-DSC method. Moreover, the hardness of the varnishes and the conversion of double bonds using the FTIR method were tested. The photopolymerization rate and the photoinitiation index, depending on the type of photoinitiator, were as follows: APOs &lt; APO blends &lt; HAPs. However, the highest coating hardness results were obtained using the least reactive photoinitiator from the APO group, i.e., Omnirad TPOL, or a mixture of three different types of acylphosphine (Omnirad BL 750). The greater effectiveness of the above-mentioned APOs over HAP was also demonstrated when using a UV LED lamp at 365 nm with a low UV dose and UV irradiance, thanks to the presence of phosphoric acid diester in the coating composition, acting as both a telogen and an antioxidant.

Effect of Aromatic Rings in AESO-VDM Biopolymers on the Local Free Volume and Diffusion Properties of Polymer Matrix

In this work, the influence of aromatic rings on the local free volume of cured mixtures of acrylate epoxidized soybean oil (AESO) and vanillin dimethacrylate (VDM) was investigated. Cross-linking took place under the influence of UV light in the presence or absence of a photoinitiator. The local free volume and its homogeneity were characterized using the Positron Annihilation Lifetime Spectroscopy (PALS) technique. It was found that increasing the content of VDM, which contains aromatic rings, caused a decrease in the local free volume of the cured polymer network, with consequences for the diffusion properties of the polymer, which were tested for the case of water. Another consequence of increasing the content of VDM was a decrease in the conversion of double bonds in the finally cured samples, characterized by near-infrared spectroscopy (NIR). This finding illustrates a case where the decrease in free volume is not necessarily related to an increase in the crosslinking density of the polymer, but is a consequence of the presence of an increase in the occupied volume of aromatic rings in the volume of the polymer.

Enhanced anti-bacterial adhesion effect of FDMA/SR833s based dental resin composites by using 1H,1H-heptafluorobutyl methacrylate as partial diluent

With the purpose of further reducing surface free energy to achieve better anti-bacterial adhesion effect of fluorinated dimethacrylate (FDMA)/tricyclo (5.2.1.0) decanedimethanol diacrylate (SR833s) based dental resin composites (DS), 1H,1H-heptafluorobutyl methacrylate (FBMA) was used to partially replace SR933s as reactive diluent. According to the degree of substitution, the obtained resin composites were marked as DSF-1 (20 wt.% of SR833s was replaced by FBMA), DSF-2 (40 wt.% of SR833s was replaced by FBMA), and DSF-3 (60 wt.% of SR833s was replaced by FBMA). Bisphenol A glycidyl dimethacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based resin composite (BT) was used as control. The influence of FBMA concentration on double bond conversion (DC), contact angle, surface free energy, anti-bacterial adhesion effect against Streptococcus mutans (S. mutans), volumetric shrinkage (VS) and shrinkage stress (SS), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL) were investigated. The results showed that FBMA addition could reduce surface free energy from 44.6 mN/m for DS to 32.9 mN/m for DSF-3, and lead to better anti-bacterial adhesion effect (the amounts of adherent bacteria decreased from 2.03 × 105 CFU/mm2 for DS to 6.44 × 104 CFU/mm2 for DSF-3). The FBMA had no negative effects on DC, VS, SS, WS, and SL. Too high a concentration of FBMA reduced FS and FM before water immersion, but the values were still higher than those of BT.

Preparation and Mechanical Properties of UV-Curable Epoxy Acrylate/Modified Aramid Nanofiber Nanocomposite Films.

In order to enhance the mechanical properties of UV-curable epoxy acrylate (EA)-based coatings, 3-(trimethoxysilyl)propyl methacrylate modified aramid nanofibers (T-ANFs) were synthesized and used as nanofillers to prepare EA/T-ANF nanocomposite films. The morphology of T-ANFs was characterized by transmission electron microscopy. The chemical structure of T-ANFs was analyzed via infrared spectroscopy, confirming successful grafting of methyl methacryloyloxy groups onto the surface of aramid nanofibers (ANFs). Real-time infrared spectroscopy was employed to investigate the influence of ANFs and T-ANFs on the photopolymerization kinetics of the EA film. The results revealed that the addition of ANFs and T-ANFs led to a decrease in the photopolymerization rate during the initial stage but had little impact on the final double bond conversion, with all samples exhibiting a conversion rate of over 83%. The incorporation of ANFs improved the tensile strength of the films while significantly reducing their Young's modulus. In contrast, the addition of T-ANFs led to a substantial increase in both tensile stress and Young's modulus of the films. For instance, the tensile strength and Young's modulus of the 0.1 wt% of T-ANF film increased by 52.7% and 41.6%, respectively, compared to the pure EA film. To further study the dispersion morphology and reinforcement mechanism, the cross-sectional morphology of the films was characterized by scanning electron microscopy.

Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures—Part I: Conversion rate and mechanical properties

Improvement in the mechanical properties of 3-dimensional (3D) printed dental prostheses is necessary to prevent wear caused by an antagonist or fracture. However, how different printing temperatures affect their mechanical properties is unclear. The purpose of this in vitro study was to evaluate the mechanical properties of 3D printed parts fabricated at different printing temperatures. Photopolymer specimens were fabricated at 3 different temperatures (room temperature, 50°C, and 70°C) using a stereolithography 3D printer. After rinsing to remove the residual monomer, the specimens were divided into 2 groups: with or without postprocessing. The viscosity of the photopolymerization resin was measured while the temperature was increased. Furthermore, the double-bond conversion (DBC) of the printed part was evaluated (n=3). Mechanical properties were investigated via dynamic mechanical analysis (n=1) and tensile testing (n=5). Statistical comparisons were performed via 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05). The DBC rates of the green condition group increased from 66.67% to 86.33% with increasing temperature. In addition, these specimens exhibited improved mechanical properties and reduced residual monomer levels. Specimens fabricated at a temperature of 70°C exhibited mechanical properties suitable for clinical application.

Ethyl-2-(tosylmethyl)acrylate: A promising chain transfer agent for the development of low-shrinkage dental composites.

To evaluate the potential of ethyl-2-(tosylmethyl)acrylate (ASEE) as chain transfer agent for the development of low-shrinkage photopolymerizable dental composites. Composites containing 10, 20 and 30mol% of ASEE in their organic matrix were formulated. Camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDAB) (0.33wt%/0.60wt%), CQ/EDAB/Ivocerin® (0.33wt%/0.60wt%/0.10, 0.25 or 0.50wt%), CQ/EDAB/SpeedCure 938 (SC-938) (0.33wt%/0.60wt%/0.30, 0.50 or 1.00wt%) and Ivocerin® (0.50wt%) were used as photoinitiator systems. The glass transition temperature (Tg) and the crosslink density were determined by DMTA measurements. The flexural strength/modulus and ambient light working time were assessed according to ISO 4049. The shrinkage force was evaluated using a universal testing machine. The double bond conversion (DBC) was determined by NIR spectroscopy. DBC, flexural strength and modulus were measured after the storage of the specimens in deionized water at 37°C for 24h. The DBC, flexural strength and modulus data were analyzed by one-way ANOVA with p=0.05 as significance level. ASEE-based composites containing the classical initiator system CQ/EDAB exhibited low mechanical properties (flexural strength/modulus) and DBC. The screening of various photoinitiator systems showed that composites based on CQ/EDAB/Ivocerin® (0.33wt%/0.60wt%/0.50wt%), Ivocerin® (0.50wt%) or CQ/EDAB/SC-938 (0.33wt%/0.60wt%/1.00wt%) were particularly attractive. Indeed, the use of these photoinitiator systems enabled the formulation of composites containing up to 30mol% ASEE exhibiting excellent mechanical properties, high DBC, good network homogeneity and low shrinkage force values. Interestingly, the addition of SC-938 did not impair the ambient light working time of the uncured composites, whereas the incorporation of 0.50wt% Ivocerin® resulted in a strong decrease of this value. The addition of the allyl sulfone ASEE in combination with the initiator system CQ/EDAB/SC-938 (0.33wt%/ 0.60wt%/ 1.00wt%) is a promising strategy to develop low-shrinkage dental composites which exhibit excellent mechanical properties, low shrinkage force, high DBC and suitable ambient light working time.

Effect of peroxide concentration on the epoxidation of vegetable seed oil

The present study focuses on the development of a novel epoxidized vegetable oil (EKO) prepared by the insitu epoxidation of Karingotta oil (KO), a non-edible feedstock with high iodine value (119 g/100 g oil). The key parameters that affect the epoxidation reaction are temperature, time, molar ratio of DB (No. of double bonds in oil): H2O2, molar ratio of DB: CH3COOH and the amount of catalyst. The effect of molar ratio of DB:H2O2 on the epoxidation of Karingotta oil is presented here. Epoxidation was carried out at three different ratios of DB: H2O2 viz, 1:1.1 (P1.1), 1:1.5 (P 1.5) and 1:2.0 (P2.0). The determination of iodine value indicated that the double bond conversion was higher for P1.5 in comparison to P1.1 and P2.0. The increase in the concentration of peroxide from 1.5 to 2.0 did not affect the double bond conversion. Further, the oxirane value increased for P1.5 compared to P1.1 However, for P2.0, the oxirane value reduced indicating the possibility of ring opening side reaction of epoxy group at higher concentration of H2O2. FTIR spectra of all the epoxidized samples exhibited characteristic peak at 827 cm−1 confirming the formation of epoxy functionality in the oil. Quantitative estimation of epoxidation was carried out using 1H NMR which indicated 43 % epoxidation for P1.1, 54 % epoxidation for P1.5 and 43 % epoxidation for P2.0. The iodine value, oxirane value and 1H NMR spectral analysis revealed that a DB:H2O2 ratio of 1:1.5 can promote significant epoxidation of Karingotta oil which can be a potential source for epoxy prepolymers.

Evaluation and Improvement of Bio-Based Sustainable Resin Derived from Formic-Acid-Modified Epoxidized Soybean Oil for Packaging Applications.

Bio-based epoxy resin materials have obtained significant attention in the packaging industry due to concerns about the environmental and economic impacts of traditional petroleum-based plastics. The aim of this research is to improve bio-based resins' properties by investigating varying formic acid contents in the presence of a green catalyst and characterizing their physical, chemical, and mechanical properties for further scaled-up bio-based resin production for industrial packaging applications. The crude soybean oil was epoxidized with formic acid as an oxidizing agent at varying equivalent weights of 10:1 to 10:10 of soybean oil: formic acid in the presence of hydrogen peroxide and choline chloride-oxalic acid as a bi-functional green catalyst. The effect of increasing the amount of formic acid used to epoxidize crude soybean oil was evaluated with infrared (IR) spectroscopy, rheological, and epoxy yield measurements. The results demonstrated that formic acid significantly influenced the epoxidation of soybean oil, leading to a higher conversion of carbon-carbon double bonds, with a selectivity of 98% when the ratio of soybean oil to formic acid was between 10:5 and 10:10. The bio-resin film was formulated using the improved epoxidized soybean oils-from ESO (10:2.5) to ESO (10:10)-and equal amounts of acrylic acid. The results showed that resin films led to an improvement in tensile strength (ca. 180 MPa) and thermal stability at 360 °C. Although further research is necessary, this study provides valuable insights for designing an effective epoxidation process for renewable sources and developing bio-resin materials for future packaging applications.