Resin Viscosity Research Articles

In situ flow state characterization of molten resin at the inner mold in injection molding

AbstractOnline viscosity information on processing lines can reflect the material flow resistance and offer valuable guidance for manufacturing across various industries. Considering the accuracy, devices, and processes involved in injection molding, characterizing the melt's flow state during material processing poses a significant challenge. To reduce investment in viscometers, avoid influencing the components' surface aesthetics due to the installation of sensors, and make the flow state detect online in mold, this study designs a rheometric mold with cylindrical runners for identifying the in situ viscosity of molten resin during injection molding. The detection conditions of injection speed and cavity pressure variations, the entrance effect, and the viscous dissipation for Polycarbonate are analyzed under various conditions. The in situ viscosity is identified and compared with the standard cross‐WLF model. The result shows that the melt velocity and cavity pressure variations during the filling process create a stable environment for in situ rheological characterization and the detected viscosity is related to the shear rate, melt temperature, and channel dimension in injection molding. The designed mold with cylindrical runners for determining the in situ thermal‐rheological behavior of polymer is distinguished successfully and exhibits prospects for the development of low‐cost, nondestructive, and inner‐mold measurement in manufacturing applications.

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

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

3d Printing of High Viscosity UV-curable Resin for Highly Stretchable And Resilient Elastomer.

Vat photopolymerization prepared elastomers usually exhibit unsatisfied mechanical properties due to their insufficient growth of molecular weight upon UV exposure. Increasing the weight ratio of oligomer in the resin system is an effective approach to enhance the mechanical properties, yet the viscosity of the UV-curable resin increased dramatically which makes it difficult to be used. Here, a linear scan-based vat photopolymerization (LSVP) system which can print high-viscosity resin was carried out to 3D print the oligomer-dominated UV-curable resin via a dual-curing mechanism. Briefly, a polyurethane methacrylate blocking (PUB) oligomer is first synthesized and then mixed with a commercialized bifunctional oligomer, photoinitiator, and primary amine as a chain extender to prepare high-viscosity UV-curable resin for LSVP system. Through thermal treatment, deblocked isocyanate is further crosslinked with a chain extender to construct a highly entangled polymer chain network. The optimal thermal treatment parameters are investigated. Simultaneously, the resilience of the 3D-printed elastomer was evaluated by continuous tensile loading and unloading tests. Subsequently, complex structured elastomers were printed, exhibiting favorable mechanical durability without defects. The results obtained from this work will provide a reference for preparing elastomeric devices with excellent physical properties and expand the application fields of vat photopolymerization. This article is protected by copyright. All rights reserved.

Exploring Gel-Point Identification in Epoxy Resin Using Rheology and Unsupervised Learning.

Any thermoset resin's processing properties and end-use performance are heavily influenced by the gel time. The complicated viscosity of resin as a function of temperature is investigated in this work, with a particular emphasis on identifying the gel point and comprehending polymerization. Rheology studies carried out using a plate-plate controlled stress rheometer under isothermal conditions were used to compare three experimental techniques for figuring out an epoxy resin's gel point. We also look at the basic modifications that take place during polymerization. We verify the reliability of the three strategies by including Principal Component Analysis (PCA), an unsupervised machine learning methodology. PCA assists in uncovering hidden connections between these methods and various affecting factors. PCA serves a dual role in our study, confirming method validity and identifying patterns. It sheds light on the intricate relationships between experimental techniques and material properties. This concise study expands our understanding of resin behavior and provides insights that are essential for optimizing resin-based processes in a variety of industrial applications.

Effect of novel furan‐based ester reactive diluent on structure and properties of UV‐crosslinked acrylated rapeseed oil

AbstractUnsaturated furan‐based ester (UES) was prepared by green electrosynthesis using a single‐cell setup and inexpensive graphite electrodes. The UES was validated as a reactive diluent for a bio‐based acrylated rapeseed oil (ARO). UV‐light photopolymerization of the bio‐based resin was initiated using a diphenyl (2,4,6‐trimethylbenzoyl)phosphine oxide (TPO) radical photoinitiator. The addition of 20 wt% UES to ARO dropped the resin viscosity by 1.6‐fold. Incorporating 5 wt% UES into the ARO resin increased crosslinking density νe from 1.07 to 1.65 mol/m3. Fourier‐transform infrared spectroscopy (FT‐IR) spectra revealed that ARO has been grafted with UES. The UES functional moieties promote the formation of soft mobile dangling chain end segments in the developed macromolecular network. UV‐cured thermoset polymer reveals distinct morphologies in SEM micrographs, indicating notable structural changes with the addition of UES. A total of 5 wt% UES increased tensile strength from 0.49 to 0.55 MPa and storage modulus from 7.9 to 12.0 MPa at room temperature (22 ± 1 °C). The biodegradability in composting conditions was investigated, and up to 28% of the initial mass was lost after 60 days. UES was shown as to be efficient reactive diluent that can successfully replace fossil‐based acrylate monomers in vegetable oil‐based thermoset polymer synthesis.

A novel recycling framework for transforming uncured aerospace prepreg offcuts into a strand-based compression moulding compound with adjustable flow-compaction and curing behaviours

Aerospace composites manufacturers discard anywhere from 30 to 50% of their uncured prepreg during the ply-cutting phase of manufacturing. This waste is attributed to nesting pattern inefficiencies caused by restrictive production schedules, fixed prepreg roll widths, and limited material out-life. Previous studies have explored the possibility of transforming offcuts into strand-based compression moulding compounds, but have been limited by the processing mismatch between autoclave curing and compression moulding. This article introduces a recycling framework which employs comprehensive material characterization and targeted elevated temperature staging to produce a recyclate with tailorable processing characteristics without the need for additional resins or fillers. The influence of resin viscosity on prepreg flow-compaction is presented and a software tool is introduced which generates process maps for selecting optimal staging based on desired moulding temperature, cure time and resin viscosity.

Effects of heat treatment on the microstructure and flexural mechanical properties of carbon fiber reinforced composite cured by electron beam

Carbon fiber (CF)-reinforced composite materials are attracting attention in the automobile and aerospace industries based on their light weight and excellent mechanical properties. Electron beam curing technology is replacing the thermal curing process and can improve productivity by shortening the curing time of CF-reinforced composite materials to minutes. However, the electron beam-cured CF-reinforced composite materials have weak flexural strength. We have found that the deterioration of flexural strength of electron beam-cured CF-reinforced composites can be solved by heat treatment in a vacuum bag prior to the electron beam curing process. Through heat treatment under vacuum, the viscosity of the matrix resin was lowered, and voids between the laminated surfaces of the CF prepregs could be removed. Through this approach, the flexural strength of the electron beam cured composite material reached 1.6 GPa, which was approximately 65% improved compared to the non-heat treated material. In addition, the energy distribution transmitted when the composite material is irradiated with an electron beam was simulated using the Geant4 code. It was confirmed that the nonlinear distribution of energy transmitted to the inside of the specimen according to the electron beam energy should be carefully considered in the design of the product shape and when setting the electron beam irradiation conditions.

Role of Bio-Based and Fossil-Based Reactive Diluents in Epoxy Coatings with Amine and Phenalkamine Crosslinker.

The properties of epoxy can be adapted depending on the selection of bio-based diluents and crosslinkers to balance the appropriate viscosity for processing and the resulting mechanical properties for coating applications. This work presents a comprehensive study on the structure-property relationships for epoxy coatings with various diluents of mono-, di-, and bio-based trifunctional glycidyl ethers or bio-based epoxidized soybean oil added in appropriate concentration ranges, in combination with a traditional fossil-based amine or bio-based phenalkamine crosslinker. The viscosity of epoxy resins was already reduced for diluents with simple linear molecular configurations at low concentrations, while higher concentrations of more complex multifunctional diluents were needed for a similar viscosity reduction. The curing kinetics were evaluated through the fitting of data from differential scanning calorimetry to an Arrhenius equation, yielding the lowest activation energies for difunctional diluents in parallel with a balance between viscosity and reactivity. While the variations in curing kinetics with a change in diluent were minor, the phenalkamine crosslinkers resulted in a stronger decrease in activation energy. For cured epoxy resins, the glass transition temperature was determined as an intrinsic parameter that was further related to the mechanical coating performance. Considerable effects of the diluents on coating properties were investigated, mostly showing a reduction in abrasive wear for trifunctional diluents in parallel with the variations in hardness and ductility. The high hydrophobicity for coatings with diluents remained after wear and provided good protection. In conclusion, the coating performance could be related to the intrinsic mechanical properties independently of the fossil- or bio-based origin of diluents and crosslinkers, while additional lubricating properties are presented for vegetable oil diluents.

Design of Statistical Copolypeptides as Multipurpose Hydrogel Resins in 3D Printing

AbstractHydrogels possess desirable properties for the additive manufacturing of 3D objects, but a significant challenge is to expand the range of hydrogel feedstocks with defined molecular structure and functionality while retaining mechanical properties. To this end, the design of photopolymerizable copolypeptides, derived from linear or star‐shaped architectures which can be tailored to provide control over mechanical properties and associated 3D printing performance, are reported. Based on hydroxy ethyl‐L‐glutamine and vinylbenzyl‐L‐cysteine residues, physical crosslinking via β‐motif assembly is shown to afford hydrogels with viscoelastic properties that allow their use as resins for direct ink writing (DIW) and/or direct laser writing (DLW). The strategic incorporation of vinyl benzyl units permits rapid photocrosslinking of the self‐assembled hydrogels leading to mechanically robust 3D objects. Significantly, copolypeptide architecture directly influences hydrogel resin viscosity, which affords materials with tailorable characteristics for different 3D printing techniques, highlighting the intrinsic versatility of these systems.

Application of KNN and ANN Metamodeling for RTM Filling Process Prediction.

Process simulation is frequently adopted to facilitate the optimization of the resin transfer molding process. However, it is computationally costly to simulate the multi-physical, multi-scale process, making it infeasible for applications involving huge datasets. In this study, the application of K-nearest neighbors and artificial neural network metamodels is proposed to build predictive surrogate models capable of relating the mold-filling process input-output correlations to assist mold designing. The input features considered are the resin injection location and resin viscosity. The corresponding output features investigated are the number of vents required and the resultant maximum injection pressure. Upon training, both investigated metamodels demonstrated desirable prediction accuracies, with a low prediction error range of 5.0% to 15.7% for KNN metamodels and 6.7% to 17.5% for ANN metamodels. The good prediction results convincingly indicate that metamodeling is a promising option for composite molding applications, with encouraging prospects for data-intensive applications such as process digital twinning.

The optimization of thermo-compression process parameters of continuous carbon fiber reinforced PEEK composites

Thermoplastic composites with high performance have become the primary material developed for aerospace applications. However, there are still numerous challenges for high-quality thermo-compression molding of thermoplastic composites. This paper investigated the control mechanism of porosity in continuous carbon fiber (CCF) reinforced polyether-ether-ketone (PEEK) composites based on an orthogonal molding scheme, which examines the effect of thermo-compression process parameters on porosity. Further insights were obtained regarding the correlation among molding process parameters, porosity, and mechanical properties. The experimental results indicated that the significant factors affecting the bending performance of CCF/PEEK composites were molding pressure, temperature, and sequence holding time. Moreover, the viscosity of molten PEEK resin significantly affected the porosity of the composites, and the descending order of effect on the porosity of the composites was molding temperature, holding time, and molding pressure. Based on these results, we identified the optimal molding process conditions for CCF/PEEK composites, which were 405 °C, 1.5 MPa, and 30 min.

Printability and mechanical behavior as a function of base material, structure, and a wide range of porosities for polymer lattice structures fabricated by vat-based 3D printing

Lattice structures offer desirable functionality for engineering design such as having a high strength-to-weight ratio and efficient heat exchange. Lattice parameters can be adjusted to achieve specific benchmarks such as porosity, surface area, weight, or mechanical performance. One of the biggest challenges of creating components with lattice structures is that they are difficult to fabricate with conventional methods due to their complex, highly periodic shape. Additive manufacturing (AM) techniques such as stereolithography (SLA) vat photopolymerization (VPP) have emerged as manufacturing methods for successfully creating these structures. However, a seamless characterization and subsequent understanding of the relationship between base material properties and lattice geometry across a wide range of porosity has not been fully investigated. In this study, SLA VPP was used to print structures from two distinctly different lattices, specifically the TPMS (triply periodic minimal surface) gyroid and strut-based diamond lattices, five unique photopolymer materials with varying stiffness and strength, and twenty-six levels of porosity ranging from 34% to 84%. The broad porosity sweep provides a more continuous understanding of the impact of porosity on mechanical behavior. Analysis of mechanical and volumetric properties yielded several discoveries, including substantial effects of photopolymer resin viscosity and porous volume fraction on volumetric accuracy, printability, and defects. Based on the experimental data we propose a model for predicting mechanical properties as a function of porosity that outperformed the traditional Gibson-Ashby model. The discoveries and methods included in this work provide a foundation for future analysis of mechanical and volumetric properties of 3D printed lattices across an expansive range of structural porosities and materials.

Polyfunctional phytic acid-based reactive diluent for UV-curable coating with improved flame-retardant performance and toughness

The shortcomings of oligomer resin, including its high viscosity, easy brittleness and lack of flame-retardant performance, obviously limit the application fields of the related coatings. Herein, a UV-curable polyfunctional biomass-based diluent (PAGMA) is conveniently and effectively synthesized by grafting glycidyl methacrylate onto phytic acid. The structural characterization of PAGMA is identified by FT-IR and 1H NMR tests. Moreover, PAGMA diluent is mixed with UV-curable epoxidized soybean oil-based acrylic resin (ESO-based resin), and the influences of PAGMA on the viscosity of ESO-based resin, the mechanical property and the flame-retardant efficiency of the related films are systemically researched. All results demonstrate that the viscosity of composite resin (R2 resin) with 20 wt% PAGMA reduces by 39.2% compared with that of ESO-based resin. And the toughness of the cured film (F2 film) prepared by R2 resin achieves about 1.18 MJ·m-3, which is 2.26 times as large as the cured film prepared without PAGMA (F0 film). Furthermore, the limiting oxygen index value of F2 film improves by 31.2% compared with that of F0 film, and the F2 film can self-extinguish after being ignited. Thus, the prepared polyfunctional biomass diluent can be applied to UV-curable coatings to decline the coating viscosity and enhance the comprehensive properties of coating films, which assists in broadening the application fields of UV-curable materials, especially in fire prevention.

Degradation of Kapok Fiber-Reinforced Polyester Composites with Calcium Carbonate Filler in Seawater

This research investigates the development of polyester composites reinforced with kapok fiber and CaCO3 filler to reduce environmental impact. Natural fibers, valued for their lightweight, fire resistance, cost-effectiveness, and biodegradability, are commonly used in composites. However, synthetic fibers, despite their superior mechanical properties, raise environmental concerns. The study focuses on the composites' performance, stability, and endurance in harsh conditions. Kapok fibers were manually extracted, and CaCO3 powder was sieved to 80 mesh. Composite samples were created with varying volume fractions of CaCO3 powder and kapok fibers, using polyester as the matrix. Tensile and bending tests, according to ASTM D3039 and ASTM D790 standards, were conducted on these samples. Additionally, water absorption was assessed gravimetrically, and mechanical strength degradation was studied via immersion in artificial seawater at different temperatures. Results indicated that water absorption increased with higher fiber volume fractions in the composite, primarily due to the water-absorbing capabilities of natural fibers and CaCO3 particles, surpassing that of polyester resin. Increased immersion temperatures accelerated water diffusion, impacting interactions between water molecules, polymer chains, and natural fibers. Furthermore, an increase in the CaCO3 filler volume fraction negatively affected the mechanical strength of kapok polyester-fiber composites. This was attributed to the agglomeration of CaCO3 powder, disrupting the polyester resin's viscosity and damaging the bond between kapok fiber and the matrix. The composites exhibited their highest tensile strength with 10% CaCO3 filler before immersion, but this strength decreased following exposure to high temperatures.

Polydicyclopentadiene toughened epoxy resin and its carbon fiber composites via sequential polymerization

AbstractIn this work, a dicyclopentadiene monomer/Grubbs 2 catalyst was added to a mixture of epoxy oligomers and methyl nadic anhydride to obtain a poly‐dicyclopentadiene (DCPD) modified epoxy cross‐linked network via sequential curing. The hybrid resin was used as a matrix for preparing carbon fiber composites. The results indicated that the addition of DCPD monomers significantly reduced the viscosity of the epoxy resin. The toughness and heat resistance of the co‐cured resin was improved without significant loss of strength, which was attributed to the high compatibility between epoxy and the modifier polymer. Regarding the composites, the flexural strength of the hybrid resin‐derived composite first increased and then diminished slightly. Meanwhile, the mode‐I interlaminar fracture toughness continued to increase with the increase of PDCPD content compared to the non‐modified composites. Generally, the change trend of the above properties in the composites was consistent with the change trend of the strength and toughness exhibited in the bulk resin with increasing PDCPD contents, while the change extent was inconsistent due to factors such as fiber volume content and interfacial bonding.Highlights The epoxy/PDCPD hybrid resin system was obtained via sequential curing. The PDCPD as modifier can reduce the viscosity of the epoxy curing system. The toughness and heat resistance of the PDCPD modified epoxy resin was improved. The loss in flexural strength of the hybrid resin system was insignificant. The GIC of the epoxy composites modified with PDCPD improved appreciably.

Influence of Thermoplastic Elastomer Filler on Impact Viscosity of Epoxy Resin at Low Temperatures

Influence of Thermoplastic Elastomer Filler on Impact Viscosity of Epoxy Resin at Low Temperatures

Optimization of viscosity and composition of mixture of Cu powder and acrylate based resin for vat photopolymerization of metal components

Vat photopolymerization is a technique that uses photocurable resin having photoinitiator (PI) to initiate polymerization reaction when exposed to UV light. This process forms long chains polymers by combination of small chains monomers and oligomers. Vat photopolymerization depends on various parameters. This work focusses on the optimization of viscosity and composition of acrylate resin-Cu powder mixture for vat photopolymerization of metallic samples. Anycubic acrylate-based photopolymer resin and fine copper powder is used. Five configurations (50%Cu-50%resin, 55%Cu-45%resin, 60%Cu-40%resin, 65%Cu-35%resin & 70%Cu-30%resin) are formed to determine the highest possible density in each sample. These samples are then sintered in order to optimize the sintering parameters like debinding and sintering temperatures, oxygen and carbon contents. Then, the sample with maximum Cu density is used to optimize the viscosity of mixture using ethylene glycol as diluent. It is observed that ethylene glycol is useable as it effectively reduces the viscosity of resin without altering the chemical nature and curing time of photocurable resin. By equating the viscosity of optimized Cu-resin mixture with pure resin, difference in curing times is calculated for finite thickness of layer. This shows that 28% increase in curing time is observed when Cu-resin mixture is used as compared to pure resin. Sintering profile used is good in terms of debinding and sintering temperatures however hydrogen curing environment is essential to reduce carbon and oxygen contents in final samples.

Preparation and Validation of a Longitudinally and Transversely Stiffened Panel Based on Hybrid RTM Composite Materials.

In the face of the difficulty in achieving high-quality integrated molding of longitudinally and transversely stiffened panels for helicopters by resin-matrix composite materials, we combine the prepreg process and the resin transfer molding (RTM) process to propose a hybrid resin transfer molding (HRTM) for composite stiffened panel structures. The HRTM process uses a mixture of prepreg and dry fabric to lay up a hybrid fiber preform, and involves injecting liquid resin technology. Using this process, a longitudinally and transversely stiffened panel structure is prepared, and the failure modes under compressive load are explored. The results show that at the injection temperature of the RTM resin, the prepreg resin dissolves slightly and has little effect on the viscosity of the RTM resin. Both resins have good miscibility at the curing temperature, which allows for the overall curing of the resin. A removable box core mold for the HRTM molding is designed, which makes it convenient for the mold to be removed after molding and is suitable for the overall molding of the composite stiffened panel. Ultrasonic C-scan results show that the internal quality of the composite laminates prepared using the HRTM process is good. A compression test proves that the composite stiffened panel undergoes sequential buckling deformation in different areas under compressive load, followed by localized debonding and delamination of the skin, and finally failure due to the fracture of the longitudinal reinforcement ribs on both sides. The compressive performance of the test specimen is in good agreement with the finite element simulation results. The verification results show that the HRTM process can achieve high-quality integrated molding of the composite longitudinally and transversely stiffened panel structure.

Effect of build angle, resin layer thickness and viscosity on the surface properties and microbial adhesion of denture bases manufactured using digital light processing

ObjectivesTo investigate differences in the surface properties and microbial adhesion of denture base resins for digital light processing (DLP) with varying resin layer thicknesses (LT), build angles (BA), and resin viscosities. MethodsTwo denture base resins for DLP with different viscosities (high and low) were used to prepare disk specimens applying two manufacturing parameters: 1) LT (50 or 100 μm) and 2) BA (0-, 45-, and 90-degree). Surface roughness and contact angle values were measured on the test surfaces (n=10 per group). Streptococcus oralis and Candida albicans absorbance was measured to assess microorganism attachment (n=6 per group). A three-way analysis of variance (ANOVA) was conducted, considering the main effects and their interactions (viscosity, LT, and BA). Post-hoc multiple pairwise comparisons were performed. All data were analyzed at a level of significance (P) of 0.05. ResultsLT and BA significantly affected the surface roughness and contact angle of the specimens, depending on resin viscosity (P<.001). Absorbance measurement showed no significant interaction between the three factors (P>.05). However, significant interactions were observed between viscosity and BA (P<.05) and between LT and BA (P<.05). ConclusionsRegardless of the viscosity and LT, discs with a 0-degree BA showed the least roughness. High-viscosity specimens fabricated with a 0-degree BA had the lowest contact angle. Regardless of the LT and viscosity, discs with a 0-degree BA showed the lowest S. oralis attachment. Attachment of C. albicans was the least on the disk with 50 μm LT, irrespective of the viscosity. Clinical significanceClinicians should consider the effects of LT and BA on surface roughness, contact angle, and microbial adhesion of DLP-generated dentures, which can differ depending on resin viscosity. A 50 μm LT and 0-degree BA can be used with a high-viscosity resin to fabricate denture bases with less microbial adhesion.

Performance of Polyalkyl Acrylate Additives of Various Compositions in Low-Temperature Dewaxing of Oil Raffinates

The performance of polyalkyl acrylate additives of various compositions in low-temperature dewaxing of 11 oil fractions differing in the viscosity and content of waxes, aromatic hydrocarbons, and resins was studied. The dewaxing was performed in a methyl ethyl ketone–toluene mixed solvent. For polyalkyl acrylate with pendant C16–10 alkyl chains, the raffinates can be subdivided into three groups with respect to an increase in the yield of dewaxed oils (relative to the process without additives): increase by 12–13, 5–8, and 3–4%. In most cases, introduction into such polymer of 5–30% polar groups (amino ester, amino amide, amide, oligoethylene glycol) allowed the oil yield to be additionally increased.