Volumetric Shrinkage Research Articles

Preparation and characterization of UV-Curable phosphate ester-containing acrylate resin adhesive for dental zirconia restorations

Fumed silica was utilized as a filler, methacryloyloxydecyl dihydrogen phosphate (MDP) served as a reactive monomer, and acrylate acted as a resin monomer to develop zirconia adhesives for dental acrylate resins containing phosphate esters. A uniform design, orthogonal tests, and single-variable experiments were conducted to vary the composition of each component. The effects of different composition ratios on the mechanical properties, hydrophilicity, flowability, and volumetric shrinkage of dental resin adhesives were studied in detail. The resin matrix composition included 43.6 wt% Bis-GMA, 28.2 wt% triethylene glycol dimethacrylate (TEGDMA), and 28.2 wt% hydroxyethyl methacrylate (HEMA). The photocurable system composition consisted of 4 % camphorquinone (CQ), 2.4 % ethyl 4-dimethylaminobenzoate (EDB), 3.2 % dimethylaminoethyl methacrylate (DMAEMA), and 1 % butylated hydroxytoluene (BHT). The adhesive monomer was 12 % MDP, and the filler system comprised 2 % R972 and 3 % OX50. The light curing time was set at 60 s. The adhesive exhibited optimal performance with a bonding strength of 35.9 MPa and a volumetric shrinkage of 13.3 %. According to this study, the proposed zirconia adhesive featuring a phosphate-containing acrylic ester group is a potential light-curing dental resin adhesive with a straightforward synthesis procedure, minimal volumetric shrinkage, good bonding strength, and an appropriate photocuring time.

High-purity κ-carrageenan from Kappaphycus alvarezii algae for aerogel production by supercritical CO2 drying

Carrageenan, a polysaccharide mostly extracted from Kappaphycus alvarezii (KA), is valuable for cosmetic and food uses due to large quantities of κ-carrageenan. High-pressure sequential extractions can recover high-purity carrageenan from KA, adequate for aerogel production. The biopolymer properties such as size, shape, and sulphate groups affect the gel form and aerogel characteristics. In this work, aerogels were obtained by supercritical CO2 drying, and cryogels by freeze-drying, using high-purity carrageenan, recovered by sequential high-pressure extractions (HP), and commercial carrageenan (CC). The results indicated that HP samples showed higher volumetric shrinkage (96%), firmness (254N), and envelope density (0.008g.cm-3) compared to CC samples. Aerogels presented characteristics of pore volume, surface area, and density suggesting supercritical drying as feasible method to produce porous materials. Besides, the aerogels present valuable properties compared to cryogel, including high firmness, useful for applications in packages, scaffolds, or delivery systems, a tendency that must be increasingly explored.

Shrinkage and deformation of material extrusion 3D printed parts during sintering: Numerical simulation and experimental validation

Material extrusion 3D printing (ME3DP) combined with sintering is a low-cost additive manufacturing technique for fabricating components of difficult-to-print metals, such as copper, aluminum, and ceramics. However, the sintering process includes complex material science, such as volumetric shrinkage and free structural bending, to identify the relative density and deformation of a 3D printed sample. The prediction of the relative density and deformations during the sintering process provides information to the design engineer to optimize the design of the CAD model before sintering. In this study, a phenomenological model based on constitutive equations was developed to predict the density and structural deformation during the sintering process of pure copper components fabricated by ME3DP using metal injection molding feedstock. The densification rate was determined using shrinkage estimation with an isothermal stairway heating cycle in a vertical dilatometer. Furthermore, different sets of experiments were performed with a load on the probe with long isothermal heating cycles at 850, 900, 950, 1000, and 1050 °C in a vertical dilatometer to estimate the axial viscosity of the copper. The constitutive equations were solved using the solid mechanics module with user-defined creep in COMSOL Multiphysics by considering isotropic assumptions. Two types of geometries, cube and overhanging I section, were used to predict shrinkage and deformation during the sintering process. The developed model successfully predicted the relative density based on shrinkage and structural deformation owing to gravity during the sintering process.

In-situ sol-gel process for the formulation of Bis-GMA/TEGDMA/silica dental nanocomposite

A novel dental composite based on Bis-GMA/TEGDMA resin incorporating silica nanoparticles was developed using an innovative in situ sol-gel process. This method ensures a homogeneous dispersion of fillers, effectively preventing their agglomeration during preparation. It results in an interpenetrating network in which polymer chains and silica particles are intimately mixed, thereby enhancing the structural and mechanical properties and minimizing the volumetric shrinkage of the dental restorative material.The formation of organic and inorganic network was confirmed by infrared spectroscopy. The in situ synthesis enabled uniform dispersion of silica nanoparticles within the material as evidenced by transmission electron microscopy, scanning electron microscopy and energy dispersive spectroscopy.The results showed that the prepared composite containing 50 wt% fillers achieved hardness, modulus of elasticity, compressive strength and flexural strength values of 72 HV, 10 GPa, 240 MPa, and 110 MPa, respectively. These properties are comparable to those of the commercial “Nt Premium” composite containing 75 % preformed silica nanoparticles, which has hardness, modulus of elasticity, compressive strength and flexural strength values of 68 HV, 10 GPa, 220 MPa and 95 MPa, respectively. Additionally, the study revealed a significantly reduced volumetric shrinkage of 0.5 % for our composite, compared with over 2.2 % for Nt Premium. This groundbreaking approach holds substantial promise for developing advanced dental materials, offering superior performance and enhanced longevity in clinical applications.

The Effect of Inorganic Filler Content on the Properties of BPA-Free Bulk-Fill Dental Resin Composites.

This study aimed to enhance the performance of dental resin composites (DRCs) by increasing the content of inorganic fillers while addressing potential health risks associated with Bisphenol A (BPA). To achieve this, the BPA-based resin monomer Bis-GMA was replaced with BPA-free Bis-EFMA. The study then explored the impact of varying inorganic filler contents on the physiochemical properties of Bis-EFMA-based bulk-fill dental resin composites (BF-DRCs). Four distinct Bis-EFMA-based BF-DRCs were formulated, each with different inorganic filler contents ranging from 70 wt% to 76 wt%. The study tested the depth of cure (DOC), double-bond conversion (DC), water sorption (WS), solubility (SL), and cytotoxicity of the system. It notably investigated the effects of increasing filler content on mechanical properties through flexural strength (FS), flexural modulus (FM), Vickers microhardness (VHN), and wear resistance, as well as the impact on polymerization shrinkage, including volumetric shrinkage (VS) and shrinkage stress (SS). To assess the commercial application potential of Bis-EFMA-based BF-DRC, the research used the commercially available BF-DRC Filtek Bulk-Fill Posterior (FBF) as a control. The results indicated that a higher filler content did not affect the DOC of Bis-EFMA-based BF-DRCs. Inorganic fillers at higher concentrations significantly enhanced overall mechanical properties while significantly reducing volumetric shrinkage (VS; p < 0.05). When the concentration of inorganic fillers in the resin system reached 76 wt%, most of the performance of the Bis-EFMA-based BF-DRC surpassed that of the commercial control FBF, except for FS, FM, and SS. These findings highlight the potential of Bis-EFMA-based BF-DRC as a long-term restorative material for dental applications.

Comparative estimation of fracture resistance of teeth restored with new fiber impregnated composite, short fiber composite, and nanohybrid composite – An in-vitro study

INTRODUCTION. Composite resins, used in restorative dentistry, offer enhanced esthetic and mechanical qualities. Nevertheless, the significant issue of volumetric shrinkage during polymerization remains a concern. Shrinkage-induced stress has the potential to cause marginal defects and enamel and cuspal fractures, especially in high stress-bearing areas. The present study aimed at assessing and comparing the fracture resistance and fracture patterns of teeth restored with new impregnated cubical composite, short fiber reinforced composite, and nanohybrid composite in mesio-occlusal-distal (MOD) cavities.MATERIALS AND METHODS. This was an in-vitro study comprising 45 extracted premolars cleaned and mounted in resin blocks. The MOD cavities were prepared in all the samples and were divided into three groups; Group I samples restored using ESPE Filtek Z350 XT restorative composite syringeTM, Group II using GC EverX posterior compositeTM (4mm), and Group III using Fibrafill cube S. Restorations were finished and polished.RESULTS. The mean fracture resistance was 844.5±264.8, 1249.7±518.3, and 1240.8±453.3 in Group I, II, and III, respectively. Group II and III fracture resistance was comparable (p=1.00) but higher than Group I (p=0.03 with Group II, p = 0.04 with Group III). No significant difference was present in the favourable and nonfavourable fracture patterns between the three groups (p=0.108).CONCLUSIONS. Short fiber and cubic fiber integrated composites performed similarly in terms of fracture resistance resulting in favourable fracture, however better over conventional nanohybrid composites.

Dental Composite Performance Prediction Using Artificial Intelligence.

There is a need to increase the performance and longevity of dental composites and accelerate the translation of novel composites to the market. This study explores artificial intelligence (AI), specifically machine learning (ML), to predict the performance outcomes (POs) of dental composites from their composite attributes (CAs). An extensive dataset from over 200 publications was built and refined to 233 samples with 17 CAs and 7 POs. Nine ML models were evaluated for PO prediction performance using classified data, and Five ML models were evaluated for PO regression analysis. The KNN model excelled in predicting flexural modulus (FlexMod), Decision Tree model in flexural strength (FlexStr) and volumetric shrinkage (ShrinkV), and Logistic Regression and SVM models in shrinkage stress (ShrinkStr). Receiver operating characteristic area under the curve (ROC AUC) analysis confirmed these results but found that Random Forest was more effective for FlexStr and ShrinkV, suggesting the possibility of Decision Tree overfitting the data. Regression analysis revealed that the Voting Regressor was superior for FlexMod and ShrinkV predictions, while Decision Tree Regression was optimal for FlexStr and ShrinkStr. Feature importance analysis indicated TEGDMA is a key contributor to FlexMod and ShrinkV, BisGMA and UDMA to FlexStr, and depth of cure, degree of monomer-to-polymer conversion, and filler loading to ShrinkStr. There is a need to conduct a full analysis using multiple ML models because different models predict different POs better, and for a large, comprehensive dataset to train robust AI models to facilitate the prediction and optimization of composite properties and support the development of new dental materials.

Octaphenyl-POSS nanoparticles dispersed thick polyvinyl alcohol/acrylamide photopolymer with low volumetric shrinkage and high diffraction efficiency

Relatively high volumetric shrinkage induced by polymerization of photopolymer severely limits its applications in high-density holographic storage. In this paper, what we believe to be a novel organic-inorganic hybrid nanoparticles (NPs) of octaphenyl-polyhedral Oligomeric silsesquioxane (POSS) are employed into polyvinyl alcohol (PVA)/acrylamide photopolymer with 300µm thickness. By optimizing the concentration of octaphenyl-POSS, the volumetric shrinkage is successfully suppressed from 1.11% to 0.41%, and satisfies the requirements of commercial holographic data storage (HDS) material. Moreover, the introduction of POSS NPs does not sacrifice other holographic recording capacities. Contrarily, the diffraction efficiency of photopolymer after dispersing 2‰(w/v) POSS increases from 86% to 90%. The physical mechanism of enhanced capacities is discussed by using photopolymerization and NPs diffusion process. To our knowledge, this is the best results of PVA/acrylamide photopolymer with low volumetric shrinkage, high diffraction efficiency and angular selectivity. The POSS-dispersed photopolymer system is expected to have good application prospects in angular-multiplexing high-density 3-D holographic storage.

Synthesis of low-cost refractory cordierite for solar thermal storage: Characterization of mechanical, thermal and physical stability during thermal shock cycles

To guarantee the efficiency of solar thermal energy production, the thermal storage material must have exceptional resistance to thermal shock to withstand prolonged thermal cycles. In addition, it must have specific properties tailored to the requirements of this field. In this study, we developed a refractory cordierite for solar thermal storage, characterized by very high thermophysical properties, from an initial formulation containing 20 % of abundant clays. The properties of materials sintered at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1250 °C were assessed by a series of analyses including X-ray diffraction (XRD), mass loss, volumetric shrinkage, bulk density, and porosity, scanning electron microscopy (SEM), thermal conductivity, thermal diffusivity, thermal storage capacity, chemical resistance, and mechanical testing. The incorporation of natural clays, rich in sintering aid elements, facilitated the formation of 74 % α-cordierite at 1200 °C and 92 % at 1250 °C, significantly enhancing the material's densification. Materials sintered at 1250 °C and containing 92 % refractory cordierite were subjected to 50 thermal shock cycles from 500 °C to 0 °C. The obtained materials showed excellent mechanical properties, including compressive strength of 398 MPa, low porosity of 0.21 %, density of 2.52 g/cm3, zero mass loss in acidic and basic environments for 30 days, and very high values of heat capacity (3429.80 J/(kg·K)), thermal conductivity (2.08 W/(m·K)) and thermal diffusivity (0.84 mm2/s) at room temperature.

3D micro-CT and O-PTIR spectroscopy bring new understanding of the influence of filler content in dental resin composites

BackgroundDental resin composites' performance is intricately linked to their polymerisation shrinkage characteristics. This study compares polymerisation shrinkage using advanced 3D micro-computed tomography (micro-CT) and traditional 2D linear assessments. It delves into the crucial role of filler content on shrinkage and the degree of conversion in dental resin composites, providing valuable insights for the field. MethodsFive experimental dental composite materials were prepared with increasing filler contents (55–75 wt%) and analysed using either 3D micro-CT for volumetric shrinkage or a custom-designed linometer for 2D linear shrinkage. The degree of conversion was assessed using Optical Photothermal Infrared (O-PTIR) and Fourier-Transform Infrared (FTIR) spectroscopy. Light transmittance through a 2-mm layer was evaluated using a NIST-calibrated spectrometer. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) examined surface morphology and elemental distribution. Correlation between the investigated parameters was determined using Spearman correlation analyses. ResultsThe study found significant differences in polymerisation-related properties among different filler content categories, with volumetric shrinkage consistently demonstrating higher mean values than linear shrinkage across most groups. Volumetric shrinkage decreased with increasing curing depth, showing no direct correlation between filler content and shrinkage levels at different curing depths. The results highlighted a strong negative correlation between filler content and degree of conversion, volumetric and linear shrinkage, as well as maximum shrinkage rate. Light transmittance showed a moderate correlation with the filler content and a weak correlation with other tested parameters. ConclusionsThis study underscores the importance of considering both volumetric and linear shrinkage in the design and analysis of dental composite materials. The findings advocate optimising filler content to minimise shrinkage and enhance material performance. Integrating micro-CT and O-PTIR techniques offers novel insights into dental composites' polymerisation behaviour, providing a foundation for future research to develop materials with improved clinical outcomes.

COMPARATIVE EFFECT OF WOODFLOUR AND GRANULATED RICE HUSK ON THE THERMAL INSULATION OF TERMITE HILL CLAY

This research work covered the comparative effect of wood flour (saw dust) and granulated rice husk on the thermal insulation of termite hill clay. The raw clay samples were mined from the Federal University of Technology Akure Campus and processed. Likewise, the saw dust and rice husk were also processed and grinded. The clay samples and the additives were sieved to obtain 300 microns and were mixed in predetermined proportions of 0, 2, 4, 6, 8 and 10 wt. %. Cylindrical samples were developed from the mixtures which were compacted and then air dried before oven dried and finally fired. The fired samples were subjected to selected tests to determine their insulation and refractory properties. These tests include porosity, linear shrinkage, volumetric shrinkage, bulk density, thermalconductivity, thermal shock resistance and cold crushing tests. It was discovered that the saw dust samples meet the ASTM standard for insulating bricks while the rice husk samples did not. Saw dust samples with 2 and 8 wt. % were ones with optimum properties.

Effect of Calcium Carbide Residue on Shrinkage Mechanism of Clayey Subgrade Soil

ABSTRACT Calcium carbide residue (CCR) has been identified as an effective replacement for traditional lime for the stabilization of expansive soils. The shrinkage of expansive clay severely threatens the foundation layers’ long-term stability. The efficacy of CCR stabilization in reducing compressibility and enhancing the strength and stiffness of clay has been widely reported; however, the calcium-based additive stabilized soil tends to lose its engineered integrity under field-exposed seasonal moisture variation, specifically, shrinkage induced by prolonged drying. In this study, the shrinkage characteristic of CCR-treated clay (6%, 9%, and 12%) slurry was investigated by digital image analysis and mercury displacement method to quantify volumetric shrinkage strain. The results were compared with those of 4% and 6% lime-treated clay, which revealed the higher efficacy of CCR in reducing shrinkage strain by 47–57%. A characteristic shrinkage curve that depicted the significant variation of shrinkage phases in CCR-treated clay samples is developed. The dominance of the proportional shrinkage phase is observed in both untreated and treated clay samples. The shrinkage caused by evaporation, hydration, and decalcification is postulated in treated clays. This study is expected to contribute to the understanding of shrinkage mechanisms of CCR-treated clay and assist in the future design of stabilized embankment sections or subgrade for unpaved roads.

Optimizing hot tearing susceptibility of Al-5.5Zn-2.4 Mg-1.3Cu alloys by grain refinement, increasing mold and casting temperature

The Al-Zn-Mg-Cu alloy is widely used in automotive lightweighting and other applications due to its excellent mechanical properties. However, when this alloy is cast using metal molds, it exhibits high hot tearing susceptibility (HTS), increasing the risk of use. Volumetric shrinkage due to density differences during the transition from liquid to solid metal produces shrinkage stresses. At the same time, lacks feeding of the remaining liquid phase in the late solidification stage can also lead to hot tearing. The purpose of this paper is to present a device for quantitatively determining and optimizing HTS. The relationship between solidification shrinkage displacement and stress was tested in a quantitative way using a Self-designed T-tester equipped with stress and displacement sensors. The test results show that the reduction of grain size shifts the solidification shrinkage of the alloy and reduces the solidification shrinkage stress, which avoids hot tearing caused by higher solidification shrinkage stress and local stress inhomogeneity. Secondly, the grain size reduction increases the number of feeding channels in the solidification vulnerable stage, and more liquid phase is available for crack healing. In addition, the influence of casting process parameters on the HTS was studied.

Physico-mechanical Properties and Potential Utilization of Melia azedarach L. Grown in Quezon Province, the Philippines

The possible utilization of Bagalunga (Melia azedarach L.) was determined based on its physical and mechanical properties. Tests were done following the ASTM D143-2019 standard. Tree samples were collected from two municipalities of Quezon province, the Philippines – namely Sariaya and Unisan. The results showed that compared to the trees from Sariaya, the trees collected from Unisan had 13.48 and 14.24% higher green moisture content (MC) and basic relative density (RD), respectively. However, their tangential (TS), radial (RS), longitudinal (LS), and volumetric shrinkage (VS) were 12.21, 4.42, 28.94, and 7.83% lower than those of the former. Furthermore, the RD of M. azedarach was similar to that of Gmelina arborea, and Acacia mangium and higher than that of Falcataria falcata. As for VS, it was comparable and in some cases even higher than those of commercially used timber species with medium to low VS. For the strength properties, in both green and 12% MC conditions, the strength of trees from Unisan was significantly higher than trees from Sariaya. However, both remained within the medium strength classification – similar to Swietenia macrophylla, G. arborea, and A. mangium but higher than Eucalyptus deglupta, Hevea brasiliensis, and F. falcata. The significant effect of axial height was observed in MC, RD, LS, and VS, and minimal variation was found in the mechanical properties. Industrial tree plantation developers may consider using M. azedarach as an alternative species, with careful consideration of the axial height and location, as these factors can influence tree properties.

Natural bioink of interpenetrating network hydrogels mimicking extracellular polymeric substances for microbial immobilization in water pollution control

Artificial biomanufacturing has been developed as a promising biotechnology for water pollution control. Effective bioimmobilization techniques are limited in application because of low productivity and the difficulty in achieving both mechanical strength and biocompatibility. Bioprinting technology, using biomaterials as bioink to enable the rapid on-demand production of bioactive structures, opens a new path for bioimmobilization. In this study, mimicking extracellular polysaccharide and protein of aerobic granular sludge (AGS), sodium alginate (SA) and silk fibroin methacryloyl (SilMA) were developed as the dual-component bioink with a suitable viscosity for bioprinting hydrogel. Interpenetrating network (IPN) hydrogel beads were manufactured using 1.5% (w/v) SA combined with 20% (w/v) SilMA through physical and covalent crosslinking, which exhibited excellent structural stability and bioactivity. The addition of SilMA provided a solution to the poor mechanical stability of SA-Ca hydrogels limited by Ca2+-Na+ ionic exchange. The unique structure of SilMA contributed to the reduction of hydrogel swelling as well as the prevention of SA loss. IPN hydrogels showed a swelling rate of less than 20% compared to the high swelling rate of more than 60% for SA hydrogels. On the other hand, SA controlled the hardening induced by excessive self-assembly of SilMA and improved mass transport in SilMA hydrogels. Compared to IPN hydrogels, SilMA hydrogels experienced a 15% volumetric shrinkage and exhibited a low water content of 92%. Sonication pretreatment of the dual-component bioink not only increased the intermolecular chain entanglement to form IPN, but also led to β-sheet content in SiMA reaching 46%–48%, which resulted in the formation of stable IPN hydrogels dominated entirely by physical crosslinking. Satisfactory proliferation and viability were achieved for the encapsulated bacteria in IPN hydrogels (μmax 1.49–2.18 d−1). Further, the IPN biohydrogels could maintain structural stability as well as achieve pollutant removal for treating synthetic wastewater with high Na+ concentration of 300 mg/L. The novel SA/SilMA hydrogel bioprinting strategy established in this study offers a new direction for bioimmobilization in water pollution control and other environmental applications.

Marginal integrity and physicomechanical properties of a thermoviscous and regular bulk-fill resin composites.

To evaluate the marginal integrity (MI%) and to characterize specific properties of a thermoviscous bulk-fill resin composite, two regular bulk-fill resin composites, and a non-bulk-fill resin composite. VisCalor bulk (VBF), Filtek One Bulk Fill (OBF), and Aura Bulk Fill (ABF) were evaluated. Filtek Z250 XT (ZXT) was used as non-bulk-fill control. MI% was evaluated in standardized cylindrical cavities restored with the composites by using a 3D laser confocal microscope. The following properties were characterized: volumetric polymerization shrinkage (VS%), polymerization shrinkage stress (Pss), degree of conversion (DC%), microhardness (KHN), flexural strength (FS), and elastic modulus (EM). Data were analyzed by one-way and two-way ANOVA, and Tukey HSD post-hoc test (α = 0.05). VBF presented the highest MI% and the lowest VS% and Pss (p < 0.05). DC% ranged from 59.4% (OBF) to 71.0% (ZXT). ZXT and VBF presented similar and highest KHN than OBF and ABF (p < 0.05). ABF presented the lowest FS (p < 0.05). EM ranged from 5.5 GPa to 7.7 GPa, with the values of ZXT and VBF being similar and statistically higher than those of OBF and ABF (p < 0.05). Thermoviscous technology employed by VisCalor bulk was able to improve its mechanical behavior comparatively to regular bulk-fill resin composites and to contribute to a better marginal integrity in restorations built up in cylindrical cavities with similar geometry to a class I cavity as well. Although presenting overall better physicomechanical properties, Z250 XT presented the worst MI%. The marginal integrity, which is pivotal for the success of resin composite restorations, could be improved using VisCalor bulk-fill. The worst MI% presented by Z250 XT reinforces that non-bulk-fill resin composites shall not be bulk-inserted in the cavity to be restored.

Development of isotactic polypropylene‐based 3D printing materials with good dimensional accuracy and excellent impact properties

AbstractThe main challenge of fused deposition modeling (FDM) is the limited variety of commercially available semicrystalline polymer materials. Isotactic polypropylene (iPP), with a fast crystallization rate and high crystallinity, tends to undergo extensive volumetric shrinkage during the FDM process, further inducing severe deformation and poor dimensional accuracy in 3D‐printed parts. This study aims to develop desirable iPP‐based materials for the FDM technique through physically blending iPP and thermoplastic polyester elastomer (TPEE). TPEE retards the nonisothermal crystallization ability of iPP, as indicated by the significant decrease in crystallinity (Xc) from 47.7% for neat iPP to 28.5% for the iPP blend at a weight ratio of 30/70. The suppressed crystallization behavior accounts for a drastic decrease in the warpage degree of the 3D‐printed parts. The greater the content of TPEE is, the lower warpage the 3D‐printed parts have. Additionally, the presence of TPEE slightly influences the shear viscosity of iPP. As a result, iPP blends exhibit excellent extrudability during a typical FDM process. TPEE also enhances the impact strength of 3D‐printed parts by 168% compared to that of injection‐molded iPP. Taken together, the iPP blends developed in this work are promising FDM feedstock materials with good dimensional accuracy and excellent impact strength.

A targeted vacuum-expansion sealing strategy for long-term protection of porous coatings

While surface treatments like anodic oxidation or micro-arc oxidation (MAO) significantly enhance the surface hardness and abrasion resistance of aluminum alloys, they often leave numerous dense pores or defects that compromise their corrosion resistance. Traditional sealing methods, such as boiling water or silane treatments, frequently fail to completely seal these micro-cavities and can introduce new defects due to volumetric shrinkage of the sealants, thereby reducing the service lifespan of the coatings. In this study, we introduce a novel vacuum-expansion sealing (VE sealing) strategy aimed at providing a more effective and durable sealing treatment. This method involves filling sealants in a vacuum environment, followed by volume expansion through ring-opening polymerization. Using this approach, the porosity of the porous MAO layer is significantly reduced, with the MAO-Ves coating porosity decreasing from 8.69 % to a remarkable 0.03 %. Electrochemical tests further demonstrate that after VE sealing, the sealed MAO sample maintains a higher low-frequency impedance |Z|0.01Hz of 1.16 × 107 Ω·cm2 after 672 h. This study not only presents a valuable strategy for enhancing the corrosion resistance of MAO coating, but also provides an efficient solution for improving the hardness, abrasion-resistance, and corrosion-resistance of surface-treated aluminum alloys and magnesium alloys.

Study of Injection Molding Process to Improve Geometrical Quality of Thick-Walled Polycarbonate Optical Lenses by Reducing Sink Marks.

This study investigates the challenges and potential of conventional injection molding for producing thick-walled optical components. The research primarily focuses on optimizing process parameters and mold design to enhance product quality. The methods include software simulations and experimental validation using polycarbonate test samples (optical lenses). Significant parameters such as melt temperature, mold temperature, injection pressure, and packing pressure were varied to assess their impact on geometric accuracy and visual properties. The results show that lower melt temperatures and higher mold temperatures significantly reduce the occurrence of dimensional defects. Additionally, the design of the gate system was found to be crucial in minimizing defects and ensuring uniform material flow. Effective packing pressure was essential in reducing volumetric shrinkage and sink marks. Furthermore, we monitored the deviation between the predicted and actual defects relative to the thickness of the sample wall. After optimization, the occurrence of obvious defects was eliminated across all sample thicknesses (lenses), and the impact of the critical defect, the sink mark on the planar side of the lens, was minimized. These findings demonstrate the substantial potential of conventional injection molding to produce high-quality thick-walled parts when these parameters are precisely controlled. This study provides valuable insights for the efficient design and manufacturing of optical components, addressing the growing demand for high-performance thick-walled plastic products.

Release of contraction stress of dental resin composites by water sorption

Polymerization shrinkage of bonded resin composite restorations will result in the development of curing contraction stresses during setting and can cause debonding of the restoration or failure of the surrounding tooth structure. However, the hygroscopic expansion that occurs after exposure of the restorative to the wet oral environment can compensate for this shrinkage. ObjectivesThe purpose of this study was to determine the hygroscopic expansion of six commercial resin composites and relate it to their composition, mechanical properties, shrinkage, and contraction stress development. MethodsShort-term volumetric shrinkage and contraction stress of the different composites were measured by mercury dilatometry and a universal testing machine. The long-term contraction stress was measured by the deflection of a bilayer strip of metal and a resin composite, which were stored dry as well as wet to determine the effect of hygroscopic expansion. The curvature of the strip was measured by profilometry over a period of 3 months. ResultsThe curvature of the strip correlated well (r2 =0.74) with the initial contraction stress, showing that the contraction stress is an important factor in initial deformation. The water sorption in all specimens showed that the initial deformation, within 2–4 weeks after curing, was completely counteracted. A high correlation (r2 =0.90) between deflection and relative water sorption was found, where the relative water sorption is defined as the absolute water sorption corrected for the inorganic filler volume of the composite. SignificanceWithin a period of 2–4 weeks after curing most of the curing contraction stresses of resin composite restoratives will be released by hygroscopic expansion.