Residual Monomer Research Articles

Diallyldimethylammonium Chloride (DADMAC) in Water Treated with Poly-Diallyldimethylammonium Chloride (PDADMAC) by Reversed-Phase Ion-Pair Chromatography—Electrospray Ionization Mass Spectrometry

Poly-diallyldimethylammonium (PDADMAC) chloride is a flocculant agent extensively used in water clarification treatments. Commercial polyelectrolyte formulations often contain residual monomer (DADMAC), reaction by-products and other reactants as contaminants that could potentially affect human health. In the present study, we optimized an analytical method based on reversed-phase ion-pair chromatography coupled with mass spectrometry for quantifying ultra-trace levels of DADMAC, without preliminary treatments, in drinking water distributed by the Palermo aqueduct. The method was validated in terms of accuracy (recovery between 80 to 120%), precision (RSD < 10%), linearity range (from 0.5 to 15 µg/L), limit of quantification and limit of detection (LOQ 0.42 µg/L and LOD 0.12 µg/L). DADMAC was detected in all analysed water samples and the concentration ranged from 1.2 to 3.8 µg/L whit a mean value of 1.7 µg/L. To the best of our knowledge, this paper represents the first study concerning DADMAC concentration in water samples collected in Italy and, in this context, this paper can be considered very interesting when comparing future data on DADMAC monitoring in water. Moreover, this is one of a few cases where DADMAC was found in drinking water.

Degree of conversion and residual monomer elution of 3D-printed, milled and self-cured resin-based composite materials for temporary dental crowns and bridges

The aim of this work was to investigate the elution of residual monomers as a function of the manufacturing process, which are CAD/CAM manufacturing, self-curing and 3D printing. The experimental materials used consisted of the base monomers TEGDMA, Bis-GMA and Bis-EMA and 50 wt.% fillers. Additionally, a 3D printing resin without fillers was tested. The elution of the base monomers into the different media (water, ethanol and ethanol/water (75/25 vol. %)) at 37 °C over a period of up to 120 d as well as the degree of conversion (DC) by FTIR were investigated. No monomer elution could be detected in water. Most residual monomers in both other media were released from the self-curing material whereas the 3D printing composite released relatively little. The CAD/CAM blanks released hardly any quantitatively detectable amounts of monomers. Relative to the base composition, TEGDMA eluted less than Bis-GMA and Bis-EMA. DC did not correlate with residual monomer release; thus, leaching was determined not only by the amount of residual monomers present but by further factors as possibly network density and structure. The CAD/CAM blanks and the 3D printing composite showed similar high DC but lower residual monomer release from the CAD/CAM blank, likewise the self-curing composite and the 3D printing resin exhibited similar DC but different monomer elution. In terms of residual monomer elution and DC, the 3D printing composite seems promising as a new material class for the use as temporary dental crowns and bridges.Graphical

Effects of washing solution temperature on the biocompatibility and mechanical properties of 3D-Printed dental resin material

The use of digital manufacturing, particularly additive manufacturing using three-dimensional (3D) printing, is expanding in the field of dentistry. 3D-printed resin appliances must undergo an essential process, post-washing, to remove residual monomers; however, the effect of the washing solution temperature on the biocompatibility and mechanical properties remains unclear. Therefore, we processed 3D-printed resin samples under different post-washing temperatures (without temperature control (N/T), 30 °C, 40 °C, and 50 °C) for different durations (5, 10, 15, 30, and 60 min) and evaluated the degree of conversion rate, cell viability, flexural strength, and Vickers hardness. Increasing the washing solution temperature significantly improved the degree of conversion rate and cell viability. Conversely, increasing the solution temperature and time decreased the flexural strength and microhardness. This study confirmed that the washing temperature and time influence the mechanical and biological properties of the 3D-printed resin. Washing 3D-printed resin at 30 °C for 30 min was most efficient to maintain optimal biocompatibility and minimize changes of mechanical properties.

Cytotoxicity of dental self-curing resin for a temporary crown: an in vitro study.

Residual monomer tests using high-performance liquid chromatography and cytotoxicity tests were performed to analyze the effect on the oral mucosa of a self-curing resin for provisional crown production. A cytotoxicity test was performed to confirm whether leaked residual monomers directly affected oral mucosal cells. The cytotoxicity of the liquid and solid resin polymers was measured using a water-soluble tetrazolium (WST) test and microplate reader. In the WST assay using a microplate reader, 73.4% of the cells survived at a concentration of 0.2% liquid resin polymer. The cytotoxicity of the liquid resin polymer was low at ≤0.2%. For the solid resins, when 100% of the eluate was used from each specimen, the average cell viability was 91.3% for the solid resin polymer and 100% for the hand-mixed self-curing resin, which is higher than the cell viability standard of 70%. The cytotoxicity of the solid resin polymer was low. Because the polymerization process of the self-curing resin may have harmful effects on the oral mucosa during the second and third stages, the solid resin should be manufactured indirectly using a dental model.

Semi‐IPN superabsorbent polymer based on itaconic acid and polyvinyl alcohol with improved gel strength and salt resistance

AbstractSemi‐interpenetrating polymer network (semi‐IPN) technology was introduced in order to improve the gel strength and salt resistance of itaconic acid (IA)‐based superabsorbent polymers (SAPs). A semi‐IPN SAP based on IA and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) was synthesized. Polymerization was performed using a one‐pot method in an aqueous solution in the presence of polyvinyl alcohol (PVA). The structural and thermal properties of PVA/poly(IA‐co‐AMPS) were studied using Fourier transform infrared, differential scanning calorimetry, and thermogravimetry analysis. PVA formed strong hydrogen bonds with hydrophilic functional groups in the SAP network to improve the gel strength and thermal stability of the SAP. A PVA content of 6 wt% increased the centrifuge retention capacity and absorbency under load of the SAP to 60.1 and 16.4 g/g, respectively. Owing to the less salt‐sensitive hydroxyl groups of PVA, semi‐IPN SAP showed higher absorption (up to 26.3%) in an aqueous salt solution. The resulting SAP has a very low concentration of residual monomers (167.4 ppm). Experimental results suggest that PVA/poly(IA‐co‐AMPS) is an eco‐friendly SAP with excellent absorption properties, making it suitable for application in personal care products.

Effects of selected solvents on PMMA after prolonged exposure: unilateral NMR and ATR-FTIR investigations

Exposure of heritage plastics to solvents can cause several changes to their surface layers and bulk. The amorphous nature of certain plastics, particularly polymethyl methacrylate (PMMA), allows penetration and diffusion of low-molecular liquids, which can lead to swelling, cracking, plasticisation or stiffening, extraction and dissolution of polymer and additive components. Such phenomena compromise the visual characteristics, chemical and physical structure of heritage collections and remain, for the most part, unexplored. Research studies present contradicting evidence concerning the use of solvents and their safe application on PMMA. The main discrepancy is about PMMA being permeable to water or not. Alcohols have also triggered debates about whether they cause leaching and/or depolymerisation. This paper investigates the potential effects that selected free polar and non-polar solvents—employed in different media as cleaning systems—can have on PMMA after prolonged contact. The Hildebrand solubility theory was used to select solvents based on PMMA’s miscibility. The effects of deionised water, ethanol, isopropanol and petroleum ether are examined through a 30-day immersion study of PMMA via microscopic examination, weight change measurements, ATR-FTIR, peak height ratios, and NMR MOUSE. All four solvents extracted soluble components, i.e. unreacted residual monomer, and increased PMMA’s surface sensitivity to abrasions. Water and petroleum ether did not cause any measurable chemical or physical changes. Alcohols caused surface crystallisation and crazing, with isopropanol leading to stiffening and ethanol to plasticisation of the material. These effects, although extreme and absent in most routine cleaning timeframes, demonstrate the cumulative damage these solvents can potentially induce to PMMA.

Conditional Mitigation of Dental-Composite Material-Induced Cytotoxicity by Increasing the Cure Time

Light-cured composite resins are widely used in dental restorations to fill cavities and fabricate temporary crowns. After curing, the residual monomer is a known to be cytotoxic, but increasing the curing time should improve biocompatibility. However, a biologically optimized cure time has not been determined through systematic experimentation. The objective of this study was to examine the behavior and function of human gingival fibroblasts cultured with flowable and bulk-fill composites cured for different periods of time, while considering the physical location of the cells with regard to the materials. Biological effects were separately evaluated for cells in direct contact with, and in close proximity to, the two composite materials. Curing time varied from the recommended 20 s to 40, 60, and 80 s. Pre-cured, milled-acrylic resin was used as a control. No cell survived and attached to or around the flowable composite, regardless of curing time. Some cells survived and attached close to (but not on) the bulk-fill composite, with survival increasing with a longer curing time, albeit to <20% of the numbers growing on milled acrylic even after 80 s of curing. A few cells (<5% of milled acrylic) survived and attached around the flowable composite after removal of the surface layer, but attachment was not cure-time dependent. Removing the surface layer increased cell survival and attachment around the bulk-fill composite after a 20-s cure, but survival was reduced after an 80-s cure. Dental-composite materials are lethal to contacting fibroblasts, regardless of curing time. However, longer curing times mitigated material cytotoxicity exclusively for bulk-fill composites when the cells were not in direct contact. Removing the surface layer slightly improved biocompatibility for cells in proximity to the materials, but not in proportion to cure time. In conclusion, mitigating the cytotoxicity of composite materials by increasing cure time is conditional on the physical location of cells, the type of material, and the finish of the surface layer. This study provides valuable information for clinical decision making and novel insights into the polymerization behavior of composite materials.

Low viscosity versus high viscosity PMMA bone cement for total joint arthroplasty: Influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups, and crystallinity index on quasi-static flexural strength

The commercially available low viscosity (LV) PMMA bone cement has higher mechanical properties than high viscosity (HV) PMMA bone cement. However, the influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups and crystallinity index on flexural strength is yet to be unveiled. The present study is aimed to investigate the influence of glass transition temperature, residual monomer content, transmittance of chemical functional groups and crystallinity index that contributed to the higher flexural strength of LV bone cement compared to HV bone cement. The thermal behavior analysis indicated higher glass transition temperature and residual content for LV bone cement (87.5 ± 1.80 °C and 15.56±0.62%, respectively) as compared to HV bone cement (81±2.64 °C and 13.69±0.38%, respectively). Moreover, the chemical parameters such as relatively low residual monomer content computed using Raman spectroscopy and low transmittance of chemical functional groups found in FTIR spectra for LV bone cement imply better flexural strength compared to that of HV bone cement. Results indicated the crystallinity index was higher for LV (42.78 ± 0.54%) bone cement than HV bone cement (36.41 ± 0.18%). The difference in flexural strength between LV and HV bone cements governed by glass transition temperature, crystallinity index, residual monomer content and transmittance of chemical functional groups assists in the improvement and applications of PMMA bone cement.

Effect of topical fluoride applications on residual monomer release from resin-based restorative materials

BackgroundThe effects of topical fluoride applications on the release of monomer ingredients from resin-based dental materials by immersion in various extraction solutions are unclear. The aim of this study was to determine the effect of topical fluorides (APF and NaF) on the elution of residual monomers (Bis-GMA, TEGDMA, UDMA, and HEMA) from resin-based materials.MethodsNinety specimens were prepared, 30 bulk-fill composite resin, 30 nanohybrid universal composite resin, and 30 polyacid-modified composite resin (compomer). These were randomly divided into three groups based on fluoride application procedures. Each specimen was kept in 75% ethanol solution, and residual monomers released from materials were analyzed using high-performance liquid chromatography (HPLC) after 10 min, 1 h, 24 h, and 30 days. The groups were compared using the Mann Whitney U and Kruskal Wallis tests. Measurements were analyzed using the Friedman and Wilcoxon signed-rank tests.ResultsFluoride applications generally had no considerable effect on the amount of residual monomer released from resin-based restorative materials. The amount of monomer release after topical APF application was similar to the release in the control group and was lower than the release in the NaF group. The release of monomers from the resin-based material used in the study did not approach toxic levels at the applied time intervals. The compomer released lower amounts of monomer than other resin-based materials.ConclusionsFluoride applications do not increase monomer release from resin-based restorative materials. However, compomers should be employed by clinicians due to their lower monomer release compared to other resin restorative materials. The release of monomers from all the resin-based materials did not approach toxic levels at the applied time intervals.

From monomer to micelle: a facile approach to the multi-step synthesis of block copolymers via inline purification.

A one-pass continuous flow strategy to form block copolymer nanoaggregates directly from monomers is presented. A key development towards such a sophisticated continuous flow setup is a significant improvement in continuous flow dialysis. Often impurities or solvent residues from polymerizations must be removed before block extensions or nanoaggregate formation can be carried out, typically disrupting the workflow. Hence, inline purification systems are required for fully continuous operation and eventual high throughput operation. An inline dialysis purification system is developed and exemplified for amphiphilic block copolymer synthesis from thermal and photoiniferter reversible addition fragmentation chain transfer (RAFT) polymerization. The inline dialysis system is found to be significantly faster than conventional batch dialysis and the kinetics are found to be very predictable with a diffusion velocity coefficient of 4.1 × 10-4 s-1. This is at least 4-5 times faster than conventional dialysis. Moreover, the newly developed setup uses only 57 mL of solvent for purification per gram of polymer, again reducing the required amount by almost an order of magnitude compared to conventional methods. Methyl methacrylate (MMA) or butyl acrylate (BA) was polymerized in a traditional flow reactor as the first block via RAFT polymerization, followed by a 'dialysis loop', which contains a custom-built inline dialysis device. Clearance of residual monomers is monitored via in-line NMR. The purified reaction mixture can then be chain extended in a second reactor stage to obtain block copolymers using poly(ethylene glycol) methyl ether acrylate (PEGMEA) as the second monomer. In the last step, nano-objects are created, again from flow processes. The process is highly tuneable, showing for the chosen model system a variation in nanoaggregate size from 34 nm to 188 nm.

Determination of Acrylic Resin Monomers in Food Packaging Paper by Gas Chromatography – Tandem Mass Spectrometry (GC-MS/MS) with Formic Acid as a Protective Agent

Gas chromatography – tandem mass spectrometry (GC-MS/MS) using formic acid as a protective agent is reported for the determination of acrylic resin monomers in food contact packaging paper. The analytes were extracted by ethanol mixed with formic acid with 2-phenylethyl propionate as the internal standard. The extract was separated by a 6% cyanopropylbenzene-94% dimethylsiloxane ultra-inert chromatographic column and analyzed by GC-MS/MS in multiple reaction monitoring (MRM) mode. 13 acrylic resin monomers including acrylic acid, styrene, and acrylic ester were separated. The procedure was successfully applied for the analysis of real samples. The procedure provided a linear calibration range with detection limits from 0.16 to 0.46 mg kg−1. The mean recoveries were from 88.1% to 100.9% with relative standard deviations less than 5.4%. The residual acrylic resin monomers in packaging paper were primarily from printing base paper and varnish. Of the acrylic resin monomers, the monomers except for butyl acrylate and 2-ethylhexyl acrylate showed low migration rates. The method provides high sensitivity and good reproducibility with simple pretreatment, demonstrating application for monitoring acrylic resin monomers in food contact packaging paper.

Are 3D printed resin surgical splints safe to use in the mouth? A comparative in vitro study

IntroductionIn orthognathic surgery, surgical splints made of polymethymethacrylate or its variants are used to position the jaws before osteofixation, and occasionally left in-situ for a short duration to guide the occlusion postoperatively. However, allergic reactions can be caused by unreacted dental resin (monomers). Computer aided design/Computer Aided Manufacturing (CADCAM) surgical splints are now more commonly used than the conventionally “handmade” splints. It is unclear if these splints contain uncured residual monomers in any detectable quantity. Materials and methodsCADCAM surgical splints were made from 2 commonly used resins and compared with splints made manually with autopolymerising resin. The splints were immersed in saline at 37°C for 2 weeks to simulate use in the mouth, and the contents were analysed for uncured resin leaching with High Power Liquid Chromatography (HPLC) at different time intervals. ResultsUncured resin content was higher in the conventionally made splint (15,246µg/L on Day 1, 13,539 µg/L on Day 7, and 6,203µg/L on Day 14). One of the CADCAM resins had undetectable monomer quantities, while the other CADCAM resin demonstrated significantly less free monomer compared to the autopolymerising resin (382 µg/L on Day 1, 179 µg/L on Day 7 and 65.2 µg/L on Day 14). ConclusionCADCAM surgical splints have much lower free monomer content compared to the conventionally made splint, and are safe for clinical use.

Protezat parciale termoplastike

Thermoplastic dentures are mainly used for the therapy of partial edentulism, but not only. They are made of flexible materials, that are more resistant to breaking, and thinner than classic resin prostheses or prostheses with metal con- struction. Due to their chemical composition and the man- ner of fabrication (by injection), they are suitable for cases that show allergies to the residual monomer of classic RPD or to allergens from the metals used for the fabrication of RMD with metal construction. They are more aesthetic because their clasps are made of the same material as the prosthesis, with the color of the tooth or gingiva. Not only RPD can be fabricated from thermoplastic materials, but also full dentures, clasps, fiber-reinforced fixed partial den- tures, temporary crowns and bridges, obturators, speech therapy devices, briquettes and orthodontic retainers, trays for taking a functional impression, occlusal splints, anti “sleep apnea” devices, gingival simulators and pros- thetic implant holders (abutments).

COMPARISON OF EFFECTS OF FULLERENE C60 AND METHYL METHACRYLATE ON MASS INDEX OF INTERNAL ORGANS IN ANIMALS

In the clinic of orthopaedic dentistry, diseases of the mucous membrane caused by wearing removable dentures occupy a special place because the frequency of their occurrence and according to various authors varies from 15 to 70% of patients. Denture stomatitis is a complication resulting from wearing laminar dentures made of acrylates, which contain residual monomers having a chemical-toxic effect.&#x0D; The purpose of the study is to determine the mass coefficient of internal organs in order to assess the toxic effect of C60 fullerene on the body of rats and subsequent introduction of the material into the clinic of orthopedic dentistry.&#x0D; Objects and methods. The study was carried out on male rats divided into three groups of six animals each: I group included intact control rats; II group included animals received food with C60 fullerene; III group included animals received injectable methyl methacrylate. Conditionally therapeutic dose of fullerene C60 and methyl methacrylate was 1 ml/kg each. The studied samples were administered to rats through a metal probe every day once a day for 21 days.&#x0D; The state of peripheral blood, the functional state of the liver and the mass coefficient of the internal organs of the studied animals enable to evaluate and compare the toxic effect of fullerene C60 and methyl methacrylate.&#x0D; Results. The study has shown the introduction of C60 fullerene did not cause visible signs of intoxication and lethal consequences in the experimental animals. No animals of the main group (fullerene C60) and the comparison group (methyl methacrylate) died after the 21-day study. There were also no significant violations of the general condition and behaviour of the animals. The physiological state of experimental rats did not differ from control rats.&#x0D; In the group of intact control males, a significant increase in the body weight of rats compared to the initial values ​​was noted by 8% in the 2nd week and by 20% in the 3rd week of observation. In groups of animals that were injected with fullerene C60 and methyl methacrylate, the body weight dynamics as a whole was similar to the body weight dynamics of intact control animals. The obtained indicators point out the absence of a harmful effect of the studied drug on the physiological processes of rats.&#x0D; Administration of the nanopreparation did not have a harmful effect on internal organs (liver, heart, lungs, spleen, adrenal glands), with the exception of the kidneys and thymus, where certain changes were observed. The relative mass of the kidneys decreased statistically significantly when fullerene C60 was used, and the mass of the thymus, on the contrary, increased. Despite the statistical differences between the groups, the values ​​of the kidney mass coefficient for the use of the nanopreparation are within the physiological range and cannot be considered critical. An increase in the mass of the thymus against the background of fullerene use probably occurs as a result of the activation of the immune system upon the introduction of the investigated agent. However, hematological studies did not reveal pathological deviations in the leukocyte blood formula and significant activation of immunological processes, so it can be assumed that the increase in thymus mass coefficient is not a consequence of the toxic effect of C60 fullerene.&#x0D; Conclusion. The use of Fullerene C60 for 21 days, based on the results obtained, does not have a toxic effect on the organs and systems of male rats, does not cause any intoxication reactions and does not lead to fatal consequences.

Analytical Method for Residual Monomer Ethyl Acrylate Determination in Commercial Latex Resin using Gas Chromatography with Flame Ionization Detection

Latex (acrylic resin) produced by emulsion polymerization usually contains variable amounts of residual volatiles (free monomers). Depending on the chemical nature of the monomer, even if these compounds are present in smaller quantities than other volatiles, they can make the latex exude a strong odor and offer toxicity, as with ethyl acrylate, which may make it unfeasible for the consumer to apply the latex. In the present study, a quantitative chromatographic method using gas chromatography with a flame ionization detector (GC-FID) for industrial laboratory determination was investigated. Free ethyl acrylate monomer at a concentration level of 0.010% w/w in a resin-type latex was determined. This method showed selectivity for ethyl acrylate versus other volatiles in the sample, linearity with a coefficient of determination greater than 0.99, limits of detection and quantification of 0.001 and 0.003% w/w, respectively, accuracy and precision with recoveries above 85% and coefficients of variation below 10%. The robustness parameter demonstrated with a Pareto chart shows that the chromatographic parameters of the split ratio, injection volume and temperature impact the method performance.

Influence of postwashing process on the elution of residual monomers, degree of conversion, and mechanical properties of a 3D printed crown and bridge materials.

This study aimed to determine the effects of the postwashing method and time on the mechanical properties and biocompatibility of three-dimensional (3D) printed crown and bridge resin. DLP (digital light processing)-printed specimens produced from Nextdent crown & bridge (C&B) resins were washed separately using an ultrasonic bath and rotary washer with TPM (tripropylene glycol monomethyl ether) for 3min, 6min, 10min, 20min, and 1h. Postcuring was applied for 30min to each specimen after the washing process. The flexural strength, Vickers hardness, water sorption and solubility, degree of conversion (DC), elution of residual monomers, and biocompatibility of the specimens were evaluated. The ultrasonic bath showed greater washing efficacy by reducing the residual HEMA (2-hydroxyethyl methacrylate) from 2.0634ppm to 0.1456ppm and reducing the residual TEGDMA (triethylene glycol dimethacrylate) from 1.4862ppm to 0.1484ppm. With prolonged washing, the flexural strength significantly decreased from 129.67±6.66MPa (mean±standard deviation) to 103.17±7.20MPa, while the Vickers hardness increased slightly for the first 6min and then decreased thereafter significantly. The DC was 87.78±1.34% after 3min and then gradually decreased with extended washing time. The cytotoxicity significantly decreases with the increment of the washing time. The washing effect on the elution of residual monomers was better for an ultrasonic bath than for a rotary washer. Extending the washing time reduces the mechanical properties and cytotoxicity of the Nextdent C&B resin.

To evaluate allergic effects of the residual monomer by using auto polymerised acrylic resins amongst dentists.

Objective: To evaluate the allergic effects of the residual monomer by using auto polymerised acrylic resins amongst dentists. Study Design: Cross Sectional study. Setting: Department of Prosthdontics, Isra Dental College, Hyderabad. Period: June 2019 to October 2019. Material &amp; Methods: The study consists of 50 participants included Prosthodontist specialists, general dental practitioners and dental students. All contributors that filled a questionnaire regarding the allergic effects after using auto polymerised poly methyl methacrylate resin, identity of all participants will be kept private after taking consent. In questionnaire asked the questions from the contributors regarding the designation, qualification, usage duration, organs affected by allergy by using poly methyl meth acrylate resin, any medical treatment acquired for allergy and what kind of precautions used for prevention of allergy. Data was analyzed thru SPSS version 21. Descriptive statistics such as frequency distribution, percentage were included in Data analysis. The level of significance was set at &lt;0.05%. Results: This current study discovered that out of 50 participants, 64% were students, 25% general dentists and 10% specialists. Out of 50 participants, maximum participants 45% found the skin allergic reaction and minimum 8% found respiratory tract. Only 10 participants acquired the treatment and consults the doctor for allergic reactions and 25 participants did not acquired any treatment. Conclusion: Conclusion of this study was that the maximum contributors had allergic effects to the skin while many participants did not acquired or followed any therapeutic service to avoid surplus effects.

Analysis of Monomer Release from Different Composite Resins after Bleaching by HPLC.

(1) Background: This study aimed to examine the effect of bleaching agents on the release of triethylenae glycol dimethacrylate, 2-hydroxyethyl methacrylate, bisphenol A, urethane dimethacrylate, and bisphenol A-glycidyl methacrylate monomers, which are released from different composite resins, using the high-performance liquid chromatography (HPLC) method. (2) Methods: Ninety disc-shaped specimens were produced and immersed in artificial saliva. After different bleaching applications [office type bleaching (OB) and home type bleaching (HB)], the specimens were immersed in a 75 wt% ethanol/water solution, and the released monomers were analyzed by HPLC at predefined time intervals: 1, 7, and 28 days. The Kruskal-Wallis and Mann-Whitney U tests were conducted for statistical analysis (p = 0.05). (3) Results: The monomers were released at all times from all composite specimens. The monomer release was increased over time. The highest monomer release was detected on day 28. Bleaching applications affected monomer release. No statistical difference was found between OB and HB applications (p &gt; 0.05). The most released monomer was Bisphenol-A in all composites. (4) Conclusion: Given that a residual monomer release from composite resins has a toxic effect and that bleaching treatments increase this release, a treatment protocol should be made in accordance with the manufacturer's instructions.

Microplastics in Malaysian bottled water brands: Occurrence and potential human exposure

The World Health Organization noted that there is a growing need to determine the occurrence of microplastics in bottled water and its potential risks to human health. Thus, present study analyzes microplastics in eight major bottled water brands available in Malaysia and estimates the potential human exposure. Membrane filtration method followed by visual and polymer identifications were utilized to identify microplastics particles in these eight major bottled water brands. Microplastic concentrations in bottled water samples ranged from 8 to 22 particles/L, with an average of 11.7 ± 4.6 particles/L. Particle sizes ranging between 100 and 300 μm were dominant and accounted for approximately 31% in these bottled water brands. Fragments were the most identified microplastics in bottled water with transparent color being the most prevalent. The polyethylene terephthalate (PET) and polypropylene (PP) polymer types found in this study are consistent with prior results in that microplastics in bottled water are mainly derived from packaging materials and bottle caps. The Estimated Dietary Intake (EDI) for adults was between 0.068 and 0.19 particle/kg/day, while the EDI for children was between 0.089 and 0.25 particle/kg/day. Although consumption of bottled water was estimated to have low EDI values, the potential risks to human health should be heeded due to the presence of numerous plastic additives and residual monomers in these particles, which have the potential to increase inflammatory reactions and cytotoxicity in human body. Future studies should concentrate on understanding microplastics particles less than 1.5 μm and other associated factors (bottled material quality, consumption behaviour, bottled water storage conditions, and the frequency of bottle opening and closing) to further understand the effects of these microplastics particles on human toxicological aspects.

Direct Chemical Oxidative Polymerization of Polymelamine and its Copolymerization with Aniline for Hydrogel Supercapacitor Electrodes

In this work, we report for the first time, the direct chemical oxidative polymerization of melamine (MA) to obtain polymelamine (PME) via the initiation of a common oxidant, ammonium peroxydisulfate (APS). Characterizations of MA and PME were carried out by SEM, FTIR, XPS, NMR, and TGA measurements, and the results were compared with those from published works to verify the successful synthesis of PME. The PME was further used to initiate aniline (ANI) monomers, and an emeraldine product, called PAMx, was interestingly afforded. Moreover, APS oxidant was added into the solution as a second initiator for the polymerization of the residual monomers and remaining reactive sites on PAMx, thereby directly forming the hydrogel electrode, and labeled as PAMxS. The electrochemical performances of the PANI and PAMxS hydrogel supercapacitor electrodes were compared, and a high specific capacitance of 568 F g−1 at scan rate of 2 mV s−1 was obtained for PAM6S compared with 371 F g−1 for PANI. The facile direct oxidative synthesis approach for the preparation of PME provides an efficient route for its mass production, and its initiation ability with ANI monomers holds interesting potentials for the construction of macromolecules in conductive polymer applications.