Curing Profile Research Articles

Screening for Resistant Genes and Plasmid Curing Profile Reagent of Salmonella enterica and Listeria monocytogenes from Seafood Sold in Rivers State, Nigeria

Screening for Resistant Genes and Plasmid Curing Profile Reagent of Salmonella enterica and Listeria monocytogenes from Seafood Sold in Rivers State, Nigeria

Optimization of novel two-step curing method for die stack epoxy bonding to reduce voids in Ball Grid Array packages for high-density interconnect applications

This research explores the optimization of epoxy curing parameters to minimize void formation in 3-IC-Chip-MAPBGA packages, a subset of BGA packages, crucial components in high-density interconnect applications. The study utilizes a systematic approach involving design of experiments (DOE) assisted by statistical JMP tool to manipulate curing profiles, aiming to achieve void reduction while preserving adhesion properties. Various analytical techniques, including X-ray imaging, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), die shear strength tests, and C-Sam analysis for delamination, are employed to analyze void formation, material characteristics, mechanical properties, and structural integrity. The findings demonstrate that the sample with a 2nd step curing profile, identified as sample#3, which includes a ramp time of 15 min, a 1st step curing temperature of 90 °C with a soak time of 20 min, and a 2nd step ramp time of 20 min, exhibits the most favourable outcome in void reduction. This sample shows a notably lower void presence of 3.66 % and the highest die shear strength of 126 MPa. In contrast, the control sample, serving as a reference, displays a void percentage of 7.28 %, nearly twice as high as that of sample#3, and much lower die shear strength of 80 MPa at 25 °C. Adopting the curing profile of sample#3 also leads to a substantial 18.75 % reduction in cycle time compared to the control sample. The study highlights the importance of balancing curing parameters to mitigate void formation and maintain optimal mechanical properties, offering valuable insights for improving the reliability of high-density interconnect applications.

Using thermokinetic methods to enhance properties of epoxy resins with amino acids as biobased curing agents by achieving full crosslinking

Fibre-reinforced polymers (FRPs) are used in numerous industrial sectors and contribute to reducing CO2 emissions due to their outstanding properties in lightweight design. However, sustainable alternatives must be developed since the matrix polymers utilised contain substances hazardous to health and the environment. In widely used epoxy resins, the curing agents are mainly critical. Using biomolecules instead of synthetic curing agents can significantly reduce composites' toxicity and petrol-based carbon content. This study considerably exceeds the thermo-mechanical properties of epoxies cured with amino acids described in the literature until now. It demonstrates competitive or even better properties than state-of-the-art epoxies cured with petrol-based amine curing agents. For instance, the tensile strength of arginine-cured epoxy is more than twice as high as reported before and 13.5% higher compared to the petrol-based reference. At the same time, a high elongation at break of over 6% was accomplished, making these polymers suitable as matrix materials in FRPs. Furthermore, the glass transition onset of up to 130 °C is sufficiently high for many applications. The key to success is the development of individual curing profiles based on thermokinetic analysis. The work provides the development and analysis of several biomolecule-cured epoxies with promising property spectra.

Monte Carlo simulation of photopolymerizable ceramic suspension curing profile in vat photopolymerization

Vat photopolymerization holds promise for intricate ceramic structures through additive manufacturing. However, the scattering of ceramic pastes during printing can result in inaccuracies and defects. To address this, we propose utilizing a Monte Carlo method to account for scattering in absorbing media, predicting the curing profile of photopolymerizable ceramic suspensions. This method considers factors like the reflective air-slurry interface and the impact of particle size distributions on the curing profiles, which have been relatively overlooked in prior research. Employing physical equations, we developed a Matlab simulation program, facilitating the study of various process parameters on curing performance. The simulations accurately predict solidification width and depth for slurries with distinct volume fractions and powder particle sizes. The calculated correlation coefficient score was 0.9530 regarding curing depth in all six cases, significantly supporting the proposed method. Overall, this study underscores the potential of the Monte Carlo method in enhancing the precision of vat photopolymerization 3D printing for ceramics.

Determination of interaction parameters in a bottom-up approach employed in reactive dissipative particle dynamics simulations for thermosetting polymers.

The limitations in previous dissipative particle dynamics (DPD) studies confined simulations to a narrow resin range. This study refines DPD parameter calculation methodology, extending its application to diverse polymer materials. Using a bottom-up approach with molecular dynamics (MD) simulations, we evaluated solubility parameters and bead number density governing nonbonded interactions via the Flory-Huggins parameter and covalent-bonded interactions. Two solubility parameter methods, Hildebrand and Krevelen-Hoftyzer, were compared for DPD simulations. The Hildebrand method, utilizing MD simulations, demonstrates higher consistency and broader applicability in determining solubility parameters for all DPD particles. The DPD/MD curing reaction process was examined in three epoxy systems: DGEBA/4,4'-DDS, DGEBA/MPDA and DGEBA/DETA. Calculations for the curing profile, gelation point, radial distribution function and branch ratio were performed. Compared to MD data for DGEBA/4,4'-DDS, the maximum deviation in secondary reactions between epoxy and amine groups according to DPD simulations with Krevelen-Hoftyzer was 14.8%, while with the Hildebrand method, it was 1.7%. The accuracy of the DPD curing reaction in reproducing the structural properties verifies its expanded application to general polymeric material simulations. The proposed curing DPD simulations, with a short run time and minimal computational resources, contributes to high-throughput screening for optimal resins and investigates mesoscopic inhomogeneous structures in large resin systems.

Synthesis of diamond nanoparticles/urethane-based bio-adhesive and investigation of its morphology and thermal, physicomechanical, and biological properties

Diamond nanoparticles/urethane-based bio-adhesives (ND-U-BA) were synthesized via in-situ polymerization. Chemical structure and curing kinetics of the samples were studied by Fourier-transform infrared spectroscopy. Results showed NDs controlled the curing profile of samples. Thermal and crystalline properties were studied using differential scanning calorimetry and X-ray diffraction analyses. Results indicated hard segments had higher ordering levels in the presence of NDs which is due to the lower hydrogen bonding among polyurethane chains. Mechanical results showed ND-U-BA had higher adhesion strength due to the formation of chemical crosslinks and a controlled curing mechanism. MTT and biodegradation studies showed ND-U-BA had acceptable cell viability and degradation content. • Urethane and diamond nanoparticles/urethane-based bio-adhesives were synthesized. • Results showed ND nanoparticles had controlling effect on curing kinetic of samples. • Cell viability of bio-adhesives was improved with the ND nanoparticles’ addition. • Incorporation of ND nanoparticles increased the adhesion strength of bio-adhesive.

Sensitivity Analysis and Multi-Objective Optimization Strategy of the Curing Profile for Autoclave Processed Thick Composite Laminates.

To mitigate the risk of manufacturing defects and improve the efficiency of the autoclave-processed thick composite component curing process, parameter sensitivity analysis and optimization of the curing profile were conducted using a finite element model, Sobol sensitivity analysis, and the multi-objective optimization method. The FE model based on the heat transfer and cure kinetics modules was developed by the user subroutine in ABAQUS and validated by experimental data. The effects of thickness, stacking sequence, and mold material on the maximum temperature (Tmax), temperature gradient (ΔT), and degree of curing (DoC) were discussed. Next, parameter sensitivity was tested to identify critical curing process parameters that have significant effects on Tmax, DoC, and curing time cycle (tcycle). A multi-objective optimization strategy was developed by combining the optimal Latin hypercube sampling, radial basis function (RBF), and non-dominated sorting genetic algorithm-II (NSGA-II) methods. The results showed that the established FE model could predict the temperature profile and DoC profile accurately. Tmax always occurred in the mid-point regardless of laminate thickness; the Tmax and ΔT increased non-linearly with the increasing laminate thickness; but the DoC was affected slightly by the laminate thickness. The stacking sequence has little influence on the Tmax, ΔT, and DoC of laminate. The mold material mainly affected the uniformity of the temperature field. The ΔT of aluminum mold was the highest, followed by copper mold and invar steel mold. Tmax and tcycle were mainly affected by the dwell temperature T2, and DoC was mainly affected by dwell time dt1 and dwell temperature T1. The multi-objective optimized curing profile could reduce the Tmax and tcycle by 2.2% and 16.1%, respectively, and maintain the maximum DoC at 0.91. This work provides guidance on the practical design of cure profiles for thick composite parts.

Curing profile and marginal gap formation using a liner containing long-wavelength-absorbing photoinitiator: an in vitro study.

The aim was to evaluate the marginal-gap formation and curing profile of a new restorative technique using a liner with long-wavelength-absorbing photoinitiator (LWAP). Box-shaped preparations (6mm × 4mm × 4mm) were made in third molars. All samples were treated with Clearfill SE Bond and divided into 4 groups (n = 5), according to restorative technique used: (1) incremental technique (INC-Technique); (2) camphorquinone-based liner (CQ-Liner) + bulk-fill resin composite; (3) LWAP-based liner (LWAP-Liner) + bulk-fill resin composite; and (4) bulk-fill technique without liner (BF-Technique). The marginal gaps (%) for all the samples were measured using micro-computed tomography. The restorations were cross-sectioned, and the degree of conversion (DC) and Knoop microhardness were evaluated at different depths (0.3, 1, 2, 3, and 4mm). INC-Technique, CQ-Liner, and LWAP-Liner groups showed significantly fewer marginal gaps than those from the BF-Technique group. The BF-Technique specimens had the lowest DC and microhardness in depth. All the other techniques presented similar degree of conversion and microhardness at all the depths. The use of liners, regardless of the photoinitiator system, decreased the marginal-gap formation and improved the curing profile of bulk-filling restoration technique.

Preparation and curing process optimization of an asymmetric impregnated vacuum bag-only prepreg

One of the most significant defects, porosity, has been proven to affect the properties of composites. It is critical to reduce the porosity of composite material and the curing cost while maintaining high laminate quality for vacuum bag-only prepreg. In this paper, a rapidly cured epoxy resin system was developed, and an alkali-free glass fiber fabric prepreg suitable for vacuum bag molding was prepared by the asymmetric impregnation method. The optimal curing process for the prepreg was determined by resin curing kinetics, dielectric viscosity, initial curing temperature, and curing time of the prepreg on the laminate quality. The optimal curing profile of the prepreg was obtained. In addition, the effect of room temperature exposure time on the properties of the prepreg was also evaluated. These laminates produced by vacuum bag molding had outstanding internal quality and mechanical properties via the changes in the asymmetric impregnation process and the curing procedure.

Assembly of Surface-Mounted Devices on Flexible Substrates by Isotropic Conductive Adhesive and Solder and Lifetime Characterization.

The assembly of passive components on flexible electronics is essential for the functionalization of circuits. For this purpose, adhesive bonding technology by isotropic conductive adhesive (ICA) is increasingly used in addition to soldering processes. Nevertheless, a comparative study, especially for bending characterization, is not available. In this paper, soldering and conductive adhesive bonding of 0603 and 0402 components on flexible polyimide substrates is compared using the design of experiments methods (DoE), considering failure for shear strength and bending behavior. Various solder pastes and conductive adhesives are used. Process variation also includes curing and soldering profiles, respectively, amount of adhesive, and final surface metallization. Samples created with conductive adhesive H20E, a large amount of adhesive, and a faster curing profile could achieve the highest shear strength. In the bending characterization using adhesive bonding, samples on immersion silver surface finish withstood more cycles to failure than samples on bare copper surface. In comparison, the samples soldered to bare copper surface finish withstood more cycles to failure than the soldered samples on immersion silver surface finish.

Multi-Objective Optimization of Curing Profile for Autoclave Processed Composites: Simultaneous Control of Curing Time and Process-Induced Defects.

The contribution of this work is introducing a multi-objective optimization method based on finite element (FE) numerical simulation to simultaneously control the curing time and cure-induced defects of C-shaped composites during a curing cycle. Thermochemical and thermomechanical coupled analysis is performed and validated experimentally to understand the evolution details of temperature, degree of cure and curing deformation. Aiming to achieve the simultaneous control of manufacturing cost and composite quality, the curing profile is optimized by employing the critical factors including the total curing time, the maximum degree of cure difference, and the curing deformation. The optimization result shows that the designed curing profile can effectively reduce the curing time and guarantee the curing quality. The total curing time of the optimization is reduced by 19%. The verification experiment is also conducted to prove the accuracy and effectiveness of the proposed optimization method.

32 - A New 3D Volume-Based Method for Assessing Composites Curing Depth

Develop a new method to evaluate the curing depth of conventional and bulkfill composites based on the total volume of cure (VOC) and compare to the ISO 4049 depth of cure standard (DOC) with different mold diameters. A total of 100 samples were made from 2 bulkfill composites and 2 conventional resin-based composites, 25 samples for each material, with 5 samples per diameter of 10 mm, 8 mm, 6 mm, 4 mm, and 2 mm using stainless steel molds of 10 mm length. An individually designed 3D printed frame was attached to a metal plate using stainless steel screws in order to secure a fixed position of the molds in relation to the Valo cordless LED LCU which was clamped to the metal plate with an adjustable arm. ISO DOC was measured according to ISO 4049. Then the domed cylinders were scanned and the VOC% was measured in the Autodesk Meshmixer software using the STL files obtained from the scanned data using a E4D planmeca scanning device. Geomagic software was used for 3D comparison of curing profiles of 10 mm diameter samples. Two-way analysis of variance (ANOVA) and Tukeys test for pairwise comparison was used to analyze the data. A difference plot assembled in the geomagic software was used for 3D comparison of curing profiles ISO 4049 method that measures the center of the specimen does not represent the full potential of the LCU. With a 10 mm ∅ window of the LCU, 10 mm, 8 mm and 6 mm molds give identical results for DOC and VOC%. The difference between the bulkfill and regular composites was significant (p<0.05); bulkfill DOC was between 1.9x (Filtek) and 2.4x (Tetric) higher than for the regular composites. DOC and VOC% are both negatively influenced by smaller mold diameter (p<0.05). The non-homogenous nature of the LCU did not influence the VOC% and DOC. The non-homogenous nature beam profile of the LCU unit had an influence on the 3D curing profiles of the specimen, which can be explained with the higher absorption of the violet light from the composite Most of contemporary LCUs have diameters of the light exiting window >4 mm. since there were significant differences in DOC between ∅ 6 mm and ∅ 4 mm molds. ISO 4049 under-represents the DOC. The influence on the LCUs curing profile on ∅ 6 mm molds should be investigated in the future. The experiment should be repeated with other LCUs than the one used in this study. Results for the ISO DOC and volume of cure percent (VOC %) for different mold diameter samples for 4 materials Filtek Bulkfill one(FBO), Tetric Powerfill(TPF), Filtek Supreme (FS), and Tetric Prime(TP).

Synthesis of Novel Benzoxazines Containing Sulfur and Their Application in Rubber Compounds.

This work reports the synthesis and successful use of novel benzoxazines as reinforcing resins in polyisoprene rubber compounds. For this purpose, three new dibenzoxazines containing one (4DTP-fa) or two heteroatoms of sulfur (3DPDS-fa and 4DPDS-fa) were synthesized following a Mannich condensation reaction. The structural features of each benzoxazine precursor were characterized by 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and Raman. The new precursors showed well suited reactivity as characterized by differential scanning calorimetry (DSC) and rheology and were incorporated in rubber compounds. After the mixing, the curing profiles, morphologies and mechanical properties of the materials were tested. These results show that the structural feature of each isomer was significantly affecting its behavior during the curing of the rubber compounds. Among the tested benzoxazines, 3DPDS-fa exhibited the best ability to reinforce the rubber compound even compared to common phenolic resin. These results prove the feasibility to reinforce rubber compounds with benzoxazine resins as a possible alternative to replace conventional phenolic resins. This paper provides the first guide to use benzoxazines as reinforcing resins for rubber applications, based on their curing kinetics.

Influence of silanized bacterial cellulose on the mode I interlaminar fracture toughness of glass fiber filled with epoxy resin

ABSTRACT In the present work, the bacterial cellulose was grafted with silane coupling agent and its characteristics were determined with help of Fourier-transform infrared spectroscopy, Nuclear magnetic resonance spectroscopy. The silanized bacterial cellulose was used as toughener for both epoxy resin and glass fiber reinforced epoxy resin composites. Both the epoxy bulk composites and glass fiber-filled epoxy composites were prepared via three steps hot curing processing using 4, 4ʹ – diamino diphenyl sulfone (DDS) as hardener and salicylic acid (HX) as an accelerator. The curing profile of epoxy with curing agent was also studied with help of differential scanning calorimetry (DDS). The tensile properties, fracture toughness, and morphology of both epoxy bulk composites and glass fiber composites were investigated in detail. The mechanism fracture toughness was also proposed to explain for the improvement of interlaminar fracture toughness of glass fiber-filled epoxy composite.

Impact of Die Attach Sample Preparation on Its Measured Mechanical Properties for MEMS Sensor Applications

Abstract Computational modeling is often leveraged to design and optimize electronic packages for both performance and reliability purposes. One of the factors that affect the accuracy of computational models is the accuracy of the material properties. Microelectromechanical system sensors, in particular, are usually extremely sensitive to slightest material property changes in the package. Therefore, even small measurement variations in material characterization due to different sample preparation methods or different testing techniques can impact accuracy of computational models that are leveraged for designing or analyzing sensor performance. The challenge in material characterization is even greater for materials that require curing. Die attach polymers, for example, have strict curing profile requirements that are used during the manufacturing process. Such curing conditions are usually hard to duplicate in laboratories, and the samples used for material characterization may not necessarily be representative of the actual component in the final product. In this study, the effect of parameters such as temperature curing profile, application of pressure during curing, and sample preparation technique on temperature-dependent thermomechanical properties of two types of die attach elastomers is investigated. The mechanical properties, including the elastic modulus (E), coefficient of thermal expansion, and glass transition temperature of the die attach material, are measured using a suite of techniques such as dynamic mechanical analysis and thermomechanical analysis. The analysis is performed for a wide temperature range corresponding to typical sensor applications. It is shown that sample preparation and characterization techniques have a considerable impact on the measurements, which results in different MEMS sensor performance predictions through computational modeling.

Unravelling the Phases of Melamine Formaldehyde Resin Cure by Infrared Spectroscopy (FTIR) and Multivariate Curve Resolution (MCR).

Here, we study resin cure and network formation of solid melamine formaldehyde pre-polymer over a large temperature range via dynamic temperature curing profiles. Real-time infrared spectroscopy is used to analyze the chemical changes during network formation and network hardening. By applying chemometrics (multivariate curve resolution, MCR), the essential chemical functionalities that constitute the network at a given stage of curing are mathematically extracted and tracked over time. The three spectral components identified by MCR were methylol-rich, ether linkages-rich and methylene linkages-rich resin entities. Based on dynamic changes of their characteristic spectral patterns in dependence of temperature, curing is divided into five phases: (I) stationary phase with free methylols as main chemical feature, (II) formation of flexible network cross-linked by ether linkages, (III) formation of rigid, ether-cross-linked network, (IV) further hardening via transformation of methylols and ethers into methylene-cross-linkages, and (V) network consolidation via transformation of ether into methylene bridges. The presented spectroscopic/chemometric approach can be used as methodological basis for the functionality design of MF-based surface films at the stage of laminate pressing, i.e., for tailoring the technological property profile of cured MF films using a causal understanding of the underlying chemistry based on molecular markers and spectroscopic fingerprints.

Improving glass transition temperature of unsaturated polyester thermosets: Conventional unsaturated polyester resins

AbstractHighly crosslinkable unsaturated polyester resins (UPR) have attracted many interests in the application as reinforced matrix materials. Here, we present a systematical study of the influence of different curing conditions and styrene concentrations on resin viscosity and dynamic‐mechanical properties of the thermoset. The pure maleic Palapreg® P18‐03 was selected as model UPR because of its broad industrial use. By applying newly developed thermal curing profiles (without thermal initiators) and by raising the styrene content, the Tg of the network could be increased up to 206/215°C (1/10 Hz). For the first time, a fast curable UPR based on propylene glycol and neopentyl glycol with a Tg of up to 215°C is described. A partial substitution of problematic styrene with methylmethacrylate, tert‐butylacrylate, and maleic anhydride (MA) was studied as well. MA leads to significantly improved resin reactivity. A resin containing 42 wt% styrene and 8 wt% MA yields thermosets with remarkably improved mechanical properties and with a narrower glass transition range compared to the original P18‐03.

Sustainable approach towards enhancing thermal stability of bio-based polybenzoxazines

The present work demonstrates a sustainable approach to develop hybrid bio-based polybenzoxazines with thermal performance compatible to the petro-based analogues. Bio-based phenols undergoes Mannich like condensation with 3-aminopropyl triethoxysilane (APTES) and paraformaldehyde in ethanol as reaction medium as well as under solvent-less condition. In comparison to the synthesis in the presence of solvent, the reaction completion time was significantly reduced through solvent-less approach thereby improving the sustainability of procedure. Benzoxazine monomers were structurally characterized using Fourier transform infrared spectroscopy (FT-IR), proton and carbon nuclear magnetic spectroscopy (1H, 13C NMR). The synthesised monomers undergo thermally accelerated ring opening polymerization which was evidenced using differential scanning calorimetry (DSC). Silane functionality in monomer is sensitive to moisture and can possibly alter curing profile of resins as well as processing with time. Rheological behavior of the resins after a rest period of 30 days at room temperature was investigated to ensure solvent-less processing. Contact angle measurements on the polybenzoxazine specimen were also performed to interpret the effect of generated siloxane linkages on the hydrophobicity of material. Thermal performance of the hybrid polybenzoxazines has been studied by thermogravimetric analysis (TGA) and results have been compared with the reported petro-based polybenzoxazines.

In Situ Vibrational Probes of Epoxy Gelation.

This paper presents an efficient way to measure the curing kinetics and gel point, αgel, in epoxy resins from one single experiment. The epoxy curing reaction is herein monitored using in situ and time-resolved near-infrared absorption spectroscopy (NIR). The curing profiles over different isothermal conditions are in good agreement with DSC. Furthermore, the increase of the NIR absorption bands of aromatic rings (unreactive throughout curing) probe the cure shrinkage, as more and more aromatic rings are localized within the fixed sample volume. Therefore, the gel point is determined using the onset of the aromatic absorption increase. The results are in good agreement with the theoretical gel point, as well as DMA results. This innovative approach enables gelation measurements on epoxy neat resins and film composites with an easy-to-perform, accurate, robust, and versatile method.

One Step Synthesis of One Dimensional Nano MnO2 and Their Application as Oxidizing Agent for Polysulfide Polymers

In this work, MnO2 nanowires and nanorods have been prepared via a simple hydrothermal reaction. The morphology of MnO2 can be easily controlled by the change of the mole ratio of Mn7+ to Mn2+. And the obtained products are well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), the high-resolution TEM (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometer (XPS), etc. The obtained MnO2 samples are employed as the curing agent for polysulfide sealant. The maximum torque of the polysulfide polymer cured by MnO2 nanowires is the highest. The performances are verified by rheological tests of the curing profile, mechanical analysis, and tensile strength tests. The results demonstrate that both of the nanowires and nanorods have excellent vulcanization effects and reinforcing effects in comparison with commercial MnO2. The surface area, structure, and morphology of MnO2 are used to analyze the possible reasons for their promising application in vulcanizing agents for polysulfide rubber.