Resin Formulations Research Articles

Additive Manufacturing of Personalized Pharmaceutical Dosage Forms via Stereolithography.

The introduction of three-dimensional printing (3DP) has created exciting possibilities for the fabrication of dosage forms, paving the way for personalized medicine. In this study, oral dosage forms of two drug concentrations, namely 2.50% and 5.00%, were fabricated via stereolithography (SLA) using a novel photopolymerizable resin formulation based on a monomer mixture that, to date, has not been reported in the literature, with paracetamol and aspirin selected as model drugs. In order to produce the dosage forms, the ratio of poly(ethylene glycol) diacrylate (PEGDA) to poly(caprolactone) triol was varied with diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure TPO) utilized as the photoinitiator. The fabrication of 28 dosages in one print process was possible and the printed dosage forms were characterized for their drug release properties. It was established that both drugs displayed a sustained release over a 24-h period. The physical properties were also investigated, illustrating that SLA affords accurate printing of dosages with some statistically significant differences observed from the targeted dimensional range, indicating an area for future process improvement. The work presented in this paper demonstrates that SLA has the ability to produce small, individualized batches which may be tailored to meet patients’ specific needs or provide for the localized production of pharmaceutical dosage forms.

Enhanced thermal properties of silica nanoparticles and chitosan bio-based intumescent flame retardant Polyurethane coatings

Novel bio-based flame retardant coatings were synthesized through the process of grinding, mixing and curing process. The flame retardant coatings reinforced with silica nanoparticles (SiO2 NPs) have been prepared at five different formulation levels having F0 (Without adding SiO2 NPs), F1(2% w/w SiO2 NPs) and F2(4% w/w SiO2 NPs) combination with urethane resin, ammonium polyphosphate and chitosan. After the preparing of these formulated coatings were characterized by Flammability tests, combustion tests, and thermal stability tests. The peak heat release rate (PHRR) peak of the urethane filled with functionalized SiO2 NPs is observed to decrease dramatically with increasing functionalized SiO2 NPs loadings. An increase in the LOI value was observed with the increase in wt% of SiO2 NPs. From the UL-94 V data, it was confirmed that the F1, and F2 formulations have passed the flame test and were rated as V-0. The TGA result revealed that addition of SiO2 NPs could improve the thermal stability of the composite at 800 °C by forming high residual char. All the findings achieved suggest that the presence of SiO2 NPs in the formulation of urethane resin has shown the excellent impact as flame retardant coatings.

Vinyl sulfonamide based thermosetting composites via thiol-Michael polymerization

ObjectiveTo assess the performance of thiol Michael photocurable composites based on ester-free thiols and vinyl sulfonamides of varying monomer structures and varied filler loadings and to contrast the properties of the prototype composites with conventional BisGMA-TEGDMA methacrylate composite. MethodsSynthetic divinyl sulfonamides and ester-free tetrafunctional thiol monomers were utilized for thiol-Michael composite development with the incorporation of thiolated microfiller. Polymerization kinetics was investigated using FTIR spectroscopy. Resin viscosities were assessed with rheometry. Water uptake properties were assessed according to standardized methods. Thermomechanical properties were analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were measured on a universal testing machine in three-point bending testing mode. ResultsThe vinyl sulfonamide-based thiol-Michael resin formulation demonstrated a wide range of viscosities with a significant increase in the functional group conversion when compared to the BisGMA-TEGDMA system. The two different types of vinyl sulfonamide under investigation demonstrated significant differences towards the water sorption. Tertiary vinyl sulfonamide did not undergo visible swelling whereas the secondary vinyl sulfonamide composite swelled extensively in water. With the introduction of rigid monomer into the polymer matrix the glass transition temperature increased and so increased the toughness. Glassy thiol-Michael composites were obtained by ambient curing. SignificanceEmploying the newly developed step-growth thiol-Michael resins in dental composites will provide structural uniformity, improved stability and lower water sorption.

Influence of Modulated Photo-Activation on Shrinkage Stress and Degree of Conversion of Bulk-Fill Composites.

This study aimed to evaluate the polymerization properties of bulk-fill materials (low and high-viscosity) by using high-intensity continuous light and intermittent photo-activation in terms of polymerization shrinkage stress and degree of conversion (DC). The following Bulk-fill and Conventional nanofilled resin composites were evaluated: Filtek Z350XT Flow (3M/ESPE), SureFil SDR Flow (Dentsply), Filtek Bulk Fill Flow (3M/ESPE), Filtek Z350XT (3M/ESPE) and Filtek Bulk Fill Posterior (3M/ESPE). A LED device (DB 685, Dabi Atlante) was used for both protocols: continuous uniform and intermittent photo-activation (light-on and light-off cycles) with identical radiant exposure (14 J/cm2). The polymerization shrinkage stress (n=6) was evaluated by inserting a single increment of 12 mm3 between two stainless steel plates (6×2 mm) adapted to a Universal Testing Machine (UTM), at different times. Measurements were recorded after photo-activation. The degree of conversion was evaluated by Fourier transformed infrared spectroscope (FTIR) with an attenuated total reflectance (ATR) accessory (n=5). Data were analyzed by three-way ANOVA and Tukey's HSD (α=0.05) tests. Bulk Fill Posterior presented higher shrinkage stress values when photo-activated with the intermittent technique (p<0.05). The intermittent photo-activation increased the degree of conversion for the low-viscosity bulk-fills (p<0.05). Therefore, the use of modulated photo-activation (intermittent) must be indicated with caution since its use can influence the shrinkage stress and degree of conversion of composites, which varies according to the resin formulations.

Photocrosslinking-based 3D printing of unsaturated polyesters from isosorbide: A new material for resorbable medical devices

Clinically used tissue-engineered devices are few and far between. The search for biocompatible materials has been a great focus for the field for the past 30 years. The ones that exist are hard to work with when manufacturing patient-specific shapes with complex external and internal pore geometries because of their material and mechanical properties. Photo-cross-linkable polymers have arisen as a potential 3D printable solution for this problem. Here we present a new sugar-based polymer, isosorbide-derived polyester as a potential candidate to help fill this gap.Isosorbide-derived polyesters containing different amount of double bonds were synthesized to allow the material to be crosslinked or functionalized. Three resin formulations with different amounts of double bonds available (5, 12 and 17%) were used. After initial thermal and photo-crosslinking studies, Isosorbide-derived unsaturated polyesters were then mixed with a photoinitiator, co-crosslinker, and solvent to form a 3D printable resin formulation. Thin films of that resin were then cured using a Digital Light Projection (DLP) printer and analyzed. An attempt was made to modulate the cured thickness by adding HMB as a photoattenuator. We assessed 3D printing success and tensile green strength for the 3 resin formulations.We were able to 3D print unsaturated polyesters from isosorbide with a DLP printer when enough double bonds were present to facilitate crosslinking and curing of the material. Finally, thin films were then seeded with fibroblasts following the ISO 10993-5 protocol. These coupons were found safe (i.e., non-cytotoxic and biocompatible), potentially marking the beginning of a new approach to preparing resorbable implants for tissue engineering uses.

Enabling direct writing of an epoxy resin with thermo-activated organic thixotropes

Direct writing a thermosetting resin typically requires a rheological modifier or peripheral reaction rate-modulating equipment to enable shape fidelity during parts fabrication. This work describes the processing and characterization of low molecular weight diamide-based derivatives of hydroxystearic acid to facilitate direct writing of an epoxy resin. These low molecular weight gelators (LMWG) are thermally activated to produce sufficient yield stress for self-supporting, reactive, physical gels. These organic gelators are semi-crystalline and enable two modes of processing to produce form-stable resin formulations – cold processing and melt processing. Physical gelation occurs by assembly of the LMWG into supramolecular morphologies that vary by mode of processing. Flow of the form-stable epoxy resin is induced by yielding of the physical gel structure. When the physical gel is cured at temperatures below the melt transition of the organic gelator, the network structure likely kinetically traps the organic gelator in a metastable state. Recrystallization of the kinetically trapped organic gelator is impeded when the network is post-cured above the melt transition temperature of the organic gelator. The use of low molecular weight agents that physically gel by thermal activation, generates low viscosity solution processability and suggests that this platform may be suitable for high solids loading applications amenable to direct writing.

Evaluation of monomers derived from resorcinol as eluents of bisphenol A glycidyl dimethacrylate for the formulation of dental composite resins

ABSTRACTThe objective of this work was to synthesize two bio‐based monomers, using the resorcinol as raw material, and its effect as bisphenol A glycidyl dimethacrylate (Bis‐GMA) eluents on different chemical–physical and biological properties of experimental photopolymerizable composite resins. The acrylic 1,3‐phenylen diacrylic (1,3‐FDA) and methacrylic 1,3‐phenylen dimethacrylic (1,3‐FDMA) monomers were synthesized and fully characterized through FTIR and 1H‐NMR spectroscopies. Experimental photopolimerizable composites were formulated using Bis‐GMA/1,3‐FDA or Bis‐GMA/1,3‐FDMA as organic matrix. The materials were compared with a Bis‐GMA/TEGDMA resin‐based composite used as control. Polymerization kinetics was evaluated by means of FTIR spectroscopy. Polymerization stress was directly measured through a polymerization stress tester. The cell viability of the composites was evaluated using the MTT assay. One‐way analysis of variance and Tukey's test were used for statistical analysis. The materials formulated with the 1,3‐FDA monomer showed higher Rpmax values and lower polymerization stress values (p &lt; 0.05), while the flexural strength, water sorption, and solubility remained similar to the TEGDMA composite. Conversely, the materials formulated with the 1,3‐FDMA monomer showed a lower degree of conversion and statistically lower flexural strength (p &lt; 0.05). All materials exhibited a cellular viability close to 100%. Concerning the study conditions, the acrylic 1,3‐FDA monomer could be considered an alternative to TEGDMA in the formulation of photopolymerizable dental composite resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48576.

The Evolution of Catalysis for Alkyd Coatings: Responding to Impending Cobalt Reclassification with Very Active Iron and Manganese Catalysts, Using Polydentate Nitrogen Donor Ligands

Autoxidation processes to achieve curing of alkyd resins in paints, inks, and coatings are ubiquitous in many applications. Cobalt soaps have been employed for these applications for many decades and most of the paint and ink alkyd resin formulations have been optimized to achieve optimal benefits of the cobalt soaps. However, cobalt soaps are under increased scrutiny because of likely reclassification as carcinogenic under REACH (Registration, Evaluation, Authorisation, and Restrictions of Chemicals) legislation in Europe. This is critical, since such coatings are available for regular human contact. Alternative manganese- and iron-based siccatives have been developed to address this need for over a decade. They often show very high curing activity depending on the organic ligands bound to the metal centers. Recently, new classes of catalysts and modes of application have been published or patented to create safe paints, whilst delivering performance benefits via their unique reaction mechanisms. Besides the use of well-defined, preformed catalysts, paint formulations have also been developed with mixtures of metal soaps and ligands that form active species in-situ. The change from Co-soaps to Mn- and Fe-based siccatives meant that important coating issues related to radical-based curing, such as skinning, had to be rethought. In this paper we will review the new catalyst technologies and their performance and modes of action, as well as new compounds developed to provide anti-skinning benefits.

Structure–mechanical property relationships in acrylate networks

ABSTRACTThe objective of this work is to investigate the effect of the molecular mobility and resin formulation of UV‐curable acrylate systems on conversion and ultimate mechanical properties. Thin single‐layer films are produced from a series of nine mixtures of bisphenol A ethoxylate diacrylate, having different molecular weights (BisDAn = 2, BisDAn = 4, and a 50/50 mixture), with different amounts of tetraethylene glycol diacrylate (TEGDA) (0, 10, and 30 wt %). Fourier transform infrared analysis, tensile, and dynamic mechanical tests are carried out on UV post‐cured resins, and the results are correlated with the amount of TEGDA. A higher content of TEGDA gives rise to an increase in conversion and glass‐transition temperature. Tests on pure BisDAn = 2 and mixtures of BisDAn = 2 and BisDAn = 4 (BisDAn = 2 + 4) show that with increasing TEGDA content, the crosslink density increases. An increase in molecular weight of the acrylate monomer changes the final mechanical properties of UV‐cured products. A material having a rubber behavior is the result of this change. Next to UV post‐curing, the effect of thermal post‐curing is studied. The results show that thermal treatments affect the mechanical properties mainly if the polymer has a low crosslink density. Formulations highly loaded with TEGDA lead to polymers with high crosslink density, low network mobility, and consequently low mechanical properties if thermally treated. Correlations between, on the one hand, resin formulation and process conditions and, on the other hand, the final mechanical properties of UV‐cured systems are established allowing to optimize the structure–mechanical properties relationship in acrylate networks. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48498.

Low-Dielectric Constant Nanoporous Epoxy for Electronic Packaging

Abstract Epoxide functionalized poly(propylene carbonate) (ePPC) was included in an epoxy resin formulation and thermally decomposed to create nanoporous epoxy film. The dielectric constant of the porous epoxy was lower than the epoxy formulation control. The introduction of 30% porosity in the epoxy lowered the dielectric constant from 3.78 to 2.76. A postporosity chemical treatment further lowered the dielectric constant. Hexamethyldisilazane (HMDS) was used to terminate the pore walls with the hydrophobic silane layer and reduce both the dielectric constant and tangent loss of the porous epoxy. Two different styrene maleic anhydride crosslinking agents were used in the epoxy formulation, styrene maleic anhydride 2000 (SMA2000) and styrene maleic anhydride 4000 (SMA4000). The effect of the maleic anhydride concentration within SMA on the electrical, mechanical, and thermal properties of porous epoxy film was evaluated. Epoxy films crosslinked with SMA2000 resulted in films with a higher dielectric constant compared to films prepared with SMA4000 due to higher mole fraction of maleic anhydride within SMA2000. However, SMA2000 crosslinked films yielded films with better mechanical and thermal properties. SMA2000 crosslinked films with 30% porosity had a coefficient of thermal expansion (CTE) of 35.2 ppm/K and glass transition temperature of 143 °C.

GO-modified flexible polymer nanocomposites fabricated via 3D stereolithography

Graphene oxide (GO) induced enhancement of elastomer properties showed a great deal of potential in recent years, but it is still limited by the barrier of the complicated synthesis processes. Stereolithography (SLA), used in fabrication of thermosets and very recently in “flexible” polymers with elastomeric properties, presents itself as simple and user-friendly method for integration of GO into elastomers. In this work, it was first time demonstrated that GO loadings can be incorporated into commercial flexible photopolymer resins to successfully fabricate GO/elastomer nanocomposites via readily accessible, consumer-oriented SLA printer. The material properties of the resulting polymer was characterized and tested. The mechanical strength, stiffness, and the elongation of the resulting polymer decreased with the addition of GO. The thermal properties were also adversely affected upon the increase in the GO content based on differential scanning calorimetry and thermogravimetric analysis results. It was proposed that the GO agglomerates within the 3D printed composites, can result in significant change in both mechanical and thermal properties of the resulting nanocomposites. This study demonstrated the possibility for the development of the GO/elastomer nanocomposites after the optimization of the GO/“flexible” photoreactive resin formulation for SLA with suitable annealing process of the composite in future.

Low-Dielectric Constant Nanoporous Epoxy for Electronic Packaging

Epoxide functionalized poly(propylene carbonate) was included in an epoxy resin formulation and thermally decomposed to create nano-porous epoxy films. The dielectric constant of the porous epoxy was lower than the epoxy formulation control. The introduction of 30% porosity in the epoxy lowered the dielectric constant from 3.78 to 2.76. A post-porosity chemical treatment further lowered the dielectric constant. Hexamethyldisilazane was used to terminate the pore walls with the hydrophobic silane layer and reduce both the dielectric constant and tangent loss of the porous epoxy. Two different styrene maleic anhydride crosslinking agents were used in the epoxy formulation, SMA2000 and SMA4000. The effect of the maleic anhydride concentration within SMA on the electrical, mechanical, and thermal properties of porous epoxy film was evaluated. Epoxy films crosslinked with SMA2000 resulted in films with a higher dielectric constant compared to films prepared with SMA4000 due to higher mole fraction of maleic anhydride within SMA2000. However, SMA2000 cross-linked films yielded films with better mechanical and thermal properties. SMA2000 cross-linked films with 30% porosity had a coefficient of thermal expansion of 35.2 ppm/K and glass transition temperature of 143 °C.

Effect of isophorone diamine on curing kinetics and mechanical properties of 2-ethyl-4-methylimidazole/epoxy resin crosslinked network

Fast curing resins are the material basis for large-scale production of fiber reinforced polymer (FRP) composites. In this study, diglycidyl ether of bisphenol A (DGEBA) was cured with 2-ethyl-4-methylimidazole (2E4MI) as the main curing agent, and allyl glycidyl ether (AGE) was added to improve the processability. Based on this curing system, the effect of isophorone diamine (IPD) content on curing kinetics and mechanical properties was studied to obtain the optimal fast curing resin formulation. Both the curing kinetics and the glass transition temperature (Tg) were characterized by non-isothermal DSC, and the impact, flexural, and tensile behaviours of the cured products were tested. The gel and curing time of the curing system were characterized by rheometry and isothermal DSC test, respectively. The results demonstrated that the increasingly evident first shoulders from the non-isothermal DSC curves indicated the incorporation of addition reaction of IPD with epoxy groups in the first curing stage. The correlation between activation energy (Ea) and degree of curing (α) determined by Ozawa-Flynn-Wall methods strongly depended on the content of IPD. Moreover, the curing time of the optimal resin system was shortened to 15 min at 120 °C with guaranteed mechanical properties and the Tg was 102.50 °C.

The effect of resin formulation on the cellular morphology and mechanical properties of phenolic foams

ABSTRACTIn the present study, the effects of blowing agent concentration, surfactant, and resin viscosity on the cellular structure, density, and compressive strength of phenolic foams were investigated. The mechanism of foaming was studied by thermal analyses, as well. The scanning electron microscopy was performed to investigate the morphology of foams. The presence of surfactant was essential to obtain a foam structure. By increasing the amount of blowing agent in the formulation, the bubbles became larger. The variation of the resin viscosity had the sharp effect on the cell size and its distribution so that the cell size dropped from 108 to 77 μm in the sample with the highest viscosity. The mechanical properties were significantly affected by foam structure as well as the cell uniformity. By decreasing the average cell sizes, the compression strength and modulus were improved up to more than 60%. Finally, the optimum values for viscosity of resin and, blowing agent, and surfactant concentrations were obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48331.

Evaluation of bio-based monomers from isosorbide used in the formulation of dental composite resins

The objective of this study was to synthesize two bio-based monomers from isosorbide, the bis(allylcarbonate) isosorbide (IBAC) and the bis(methacrylate) isosorbide (IBM), and to evaluate its effect as Bis-GMA diluents in the formulation of photopolymerizable dental composite resins. The chemical structure of both bio-based monomers was determinate by means H1 NMR, C13 NMR and FTIR spectroscopies. Experimental composites comprising Bis-GMA/IBAC or Bis-GMA/IBM were formulated using 65 %wt of silanized inorganic filler. Experimental materials were compared with a control composite formulated with Bis-GMA/TEGDMA. Double bond conversion, polymerization kinetics, volumetric shrinkage, water sorption, solubility, and flexural properties were investigated. The data were analyzed by one-way ANOVA and Tukey test (α = 0.05). Flexural strength of the experimental materials was similar to the control (p = 0.733). Bis-GMA/IBM achieved the highest values of elastic modulus (p = 0.135). Bis-GMA/IBAC composite achieved the highest values of degree of conversion, while the values of Bis-GMA/IBM composite were similar to the control (p > 0.05). There were no differences in the polymerization shrinkage of the composites, however, the polymerization stress of the experimental materials was lower (p < 0.05). Finally, the cell viability test showed that the experimental resins formulated with the bio-based monomers were not cytotoxic. Due to its characteristics, IBAC and IBM monomers are potentially useful for the formulation of composite materials with applications in dentistry.

Molecular Mass-Dependent Resorption and Bone Regeneration of 3D Printed PPF Scaffolds in a Critical-Sized Rat Cranial Defect Model.

The emergence of additive manufacturing has afforded the ability to fabricate intricate, high resolution, and patient-specific polymeric implants. However, the availability of biocompatible resins with tunable resorption profiles remains a significant hurdle to clinical translation. In this study, 3D scaffolds are fabricated via stereolithographic cDLP printing of poly(propylene fumarate) (PPF) and assessed for bone regeneration in a rat critical-sized cranial defect model. Scaffolds are printed with two different molecular mass resin formulations (1000 and 1900 Da) with narrow molecular mass distributions and implanted to determine if these polymer characteristics influence scaffold resorption and bone regeneration in vivo. X-ray microcomputed tomography (µ-CT) data reveal that at 4 weeks the lower molecular mass polymer degrades faster than the higher molecular mass PPF and thus more new bone is able to infiltrate the defect. However, at 12 weeks, the regenerated bone volume of the 1900 Da formulation is nearly equivalent to the lower molecular mass 1000 Da formulation. Significantly, lamellar bone bridges the defect at 12 weeks with both PPF formulations and there is no indication of an acute inflammatory response.

Sub-acute and acute toxicity of Ferula asafoetida and Silybum marianum formulation and effect of the formulation on delaying gastric emptying

BackgroundDelayed gastric emptying play an important role in the pathology of functional dyspepsia. Owing to their functional attributes in alleviating the gastrointestinal disorders, single or polyherbal formulations have gained attention to treat the symptoms of functional dyspepsia. We have investigated the safety and efficacy of a novel formulation of Ferula asafoetida oleo resin and standardized Silybum marianum extract (Asdamarin).MethodsThe effect of asdamarin on delayed gastric emptying was investigated in Sprague Dawley rats using phenol red method. The acute and sub-acute oral toxicity was evaluated in wistar rats following OECD guidelines 425 and 407 respectively. The data were analyzed by one-way ANOVA using GraphPad Prism 5.0 software.ResultsOral administration of Asdamarin dose-dependently improved the delay in gastric emptying as evident from the significant increase in the gastrointestinal transit time (p < 0.001). The LD50 of asdamarin was estimated to be more than 2000 mg/kg. Further, in the 28-day sub-acute toxicity study, the administration of 250, 500 and 1000 mg/kg of Asdamarin did not significantly altered the feed and water consuption, body weight change, biochemical and haematological parameters compared to control animals. Macroscopic and histopathological examination of vital organs revealed no toxic signs.ConclusionThe preliminary data from the present study provides the first evidence on the possible effectiveness of novel formulation of F. Asafoatida and S. marianum extracts in alleviating the associated symptoms of functional dyspepsia. The toxicity data indicated that Asdamarin can be considered safe up to 1000 mg/kg dose.

3D Printing of Complex‐type SiOC Ceramics Derived From Liquid Photosensitive Resin

AbstractSiOC ceramics have been successfully synthesized using photosensitive resin as a liquid precursor through digital light processing 3D printing technology and pyrolysis. Liquid photosensitive resin has excellent fluidity (processable viscosity 0.068 Pa⋅s) which is beneficial for 3D printing. The liquid resin formulation was designed without solvent and filler. After researching the ratio of raw materials and temperature conditions, SiOC ceramic materials with complex structures can be produced without cracks. SiOC ceramics were characterized by SEM, XRD, Raman spectrometry and FT‐IR. The as‐prepared SiOC ceramic has excellent hardness (1.85 GPa) and high thermal conductivity (1.431 W/mK).

Mechanical properties, accuracy, and cytotoxicity of UV-polymerized 3D printing resins composed of Bis-EMA, UDMA, and TEGDMA

Statement of problemThree-dimensional printing has the potential for clinical applications, and additive manufacturing materials for dental use merit further investigation. PurposeThe purpose of this in vitro study was to evaluate the properties of materials formulated with ethoxylated bisphenol A-dimethacrylate (Bis-EMA), urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA) as 3D printing resins for ultraviolet digital light processing (UV-DLP) 3D printers and to characterize the mechanical and biological properties and accuracy of the printed objects. Material and methodsTen different light-polymerized resins were formulated using Bis-EMA, UDMA, and TEGDMA. Their viscosities were measured, and only 7 resins with viscosities lower than 1500 centipoise (cP) were selected for 3D printing and further material characterization. The light-polymerized resins were printed into representative shapes using a custom-made 3D printer equipped with a 405-nm UV-DLP projector as the light source. The printed specimens were subjected to biologic, mechanical, and accuracy tests, and the data were submitted to 1-way ANOVA and Tukey post hoc comparisons (α=.05). ResultsPhotopolymerizable resins made of Bis-EMA, UDMA, and TEGDMA were successfully formulated for 3D printing to fabricate objects of various shapes and sizes. TEGDMA served as the diluent to reduce the viscosity and increase the degree of conversion, while UDMA and Bis-EMA provided strength as demonstrated by the mechanical testing. All the printed objects passed cytotoxicity testing. The flexural strengths of the printed specimens ranged between 60 MPa and 90 MPa; flexural modulus ranged between 1.7 GPa and 2.1 GPa; and surface hardness ranged between 14.5 HV and 24.6 HV. These represent similar mechanical properties to those of currently used clinical resin materials. In the accuracy test, the resin mixture composed of 80% Bis-EMA, 10% UDMA, and 10% TEGDMA had the highest accuracy, with a 0.051-mm deviation from the original design. ConclusionsBis-EMA, UDMA, and TEGDMA are good candidates for the formulation of 3D printing resins for dental use. The printed objects demonstrated favorable biological and mechanical properties. Further, the accuracy of the printed specimens showed potential for clinical application.

Evaluation of DOPO and Nano-Silica Modified Epoxy Resin Systems as Low Viscous, Flame Retardant Additives for Infusion and Injection Processing of Carbon Fiber Reinforced Plastics

In the present study, a low viscous (complex viscosity between 200 to 500 mPas at 60 °C), flame retardant epoxy resin formulation is prepared and transferred to the carbon fiber reinforced plastic (CFRP) laminate using resin transfer molding (RTM) method. For the laminate production, a 12k carbon fiber fabric with an areal weight of 400 g/m2 is used to achieve a fiber volume content of approximately 60 vol % carbon fibers. Subsequently the unmodified laminate is produced, varying carbon fiber volume content to study its effect on flame retardant properties. As additives, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) modified epoxy resin and nanosilica particles delivered in an epoxy novolac masterbatch are added to the neat novolac resin system. The mixture is cured with isophorone diamine (IPDA) and polyetheramine hardener blend, resulting in a glass transition temperature of 104 °C for the unmodified laminate. Flame retardant properties of the materials are tested using cone calorimeter and thermal gravimetrical analysis. In addition, the mechanical behavior of the systems is evaluated via three-point bending method in static and dynamical loadings. In order to get deeper information on the resulting flame retardant mechanisms of the additives, the residual cone calorimeter char is analyzed with scanning electron microscopy, indicating the different flame retardant mechanisms of phosphorous and silica as well as the combination of both additives.