MyMedR

Displaying publications 101 - 120 of 177 in total

Abstract:

Sort:

Investigation of indentation size effect and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics

Alao AR, Mohd Azhari MA

J Mech Behav Biomed Mater, 2021 12;124:104842.
PMID: 34555624 DOI: 10.1016/j.jmbbm.2021.104842

Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics are investigated using micro-indentation and indentation-strength (IS) techniques, respectively. Vickers micro-indentations were applied on both materials at the load of 0.10-19.6 N to determine the load influence on the measured hardness. For the IS-measured fracture toughness, the load ranged from 1.96 to 19.6 N. The hardness decreased with increasing load by 20% and 18% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, indicating the ISE behaviour on both materials. The fracture toughness increased with the load by 27% and 59% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, signifying the R-curve behaviour. The ISE behaviour of both materials was analysed using the Meyer's, Hays-Kendall (HK), proportional specimen resistance (PSR), Nix-Gao (NG), modified PSR (MPSR) and elastic plastic deformation (EPD) models while the R-curve behaviour was analysed by the fractional power law. The Meyer's index of both materials was less than 2, strongly confirming the ISE existence. The HK, PSR and NG models were only suitable to determine intrinsic Vickers hardness for Li2O-2SiO2 glass ceramic while the MPSR and EPD models were successful for both materials. The fractional power law gave higher R-curve steepness for Li2O-2SiO2 than Li2O-SiO2 glass ceramics. Also, material and brittleness indices predicted, respectively, higher quasi-plasticity and better machinability for Li2O-2SiO2 than Li2O-SiO2 glass ceramics indicating superior performance in the former to the latter. Finally, this study presents a new significant insight into the micro-mechanisms of fracture tolerance behaviour of these glass ceramics which is critical to their functional performance as structural ceramics.

Matched MeSH terms: Hardness
Effect of Milling Time on the Microstructure, Physical and Mechanical Properties of Al-Al₂O₃ Nanocomposite Synthesized by Ball Milling and Powder Metallurgy

Toozandehjani M, Matori KA, Ostovan F, Abdul Aziz S, Mamat MS

Materials (Basel), 2017 Oct 26;10(11).
PMID: 29072632 DOI: 10.3390/ma10111232

The effect of milling time on the morphology, microstructure, physical and mechanical properties of pure Al-5 wt % Al₂O₃ (Al-5Al₂O₃) has been investigated. Al-5Al₂O₃ nanocomposites were fabricated using ball milling in a powder metallurgy route. The increase in the milling time resulted in the homogenous dispersion of 5 wt % Al₂O₃ nanoparticles, the reduction of particle clustering, and the reduction of distances between the composite particles. The significant grain refining during milling was revealed which showed as a reduction of particle size resulting from longer milling time. X-Ray diffraction (XRD) analysis of the nanocomposite powders also showed that designated ball milling contributes to the crystalline refining and accumulation of internal stress due to induced severe plastic deformation of the particles. It can be argued that these morphological and microstructural variations of nanocomposite powders induced by designated ball milling time was found to contribute to an improvement in the density, densification, micro-hardness (HV), nano-hardness (HN), and Young's modulus (E) of Al-5Al₂O₃ nanocomposites. HV, HN, and E values of nanocomposites were increased by ~48%, 46%, and 40%, after 12 h of milling, respectively.

Matched MeSH terms: Hardness
Fulltext Evaluation of functional properties of egg white obtained from pasteurized shell egg as ingredient in angel food cake

Tan, T.C., Kanyarat, K., Azhar, M.E.

International Food Research Journal, 2012;19(1):303-308.
MyJurnal

Pasteurized shell eggs are eggs that have been thermally treated to eliminate harmful bacteria, however the treatment may also denature some of the egg white proteins. In this study the degree of denaturation and functional properties (emulsifying, foaming, and gelling properties) of egg white obtained from pasteurized eggs (EWP) were compared with those of unpasteurized eggs (EWUP). Data from differential scanning calorimeter showed that the EWP (ovotransferin, lysozyme, and ovalbumin) denatured at lower temperatures and required lower denaturation enthalpies than EWUP, indicating a partial loss of protein structure during the pasteurization process in the pasteurized eggs. The emulsion and foam stability formed from EWP were significantly (P < 0.05) lower than those of EWUP, however the EWP formed stronger gels than EWUP. To assess suitability of EWP as a cake ingredient, angel food cake was prepared using both egg whites. As compared to EWUP-cake, EWP-cake was significantly (P < 0.05) lower in volume, cohesiveness and springiness values, but significantly (P < 0.05) higher in hardness, gumminess and chewiness. Overall, the sensory panelists gave significantly (P < 0.05) higher scores for angel food cake prepared with EWUP. The differences in functional properties of egg white proteins and the quality of cake were due mainly to the higher levels of denaturation attained by EWP as a result of the pasteurization process.

Matched MeSH terms: Hardness
Fulltext The ability of Zea mays ears (Young Corn) powder in enhancing nutritional composition and changing textural properties and sensory acceptability of yeast bread

Lim, J.Y., Wan Rosli, W.l.

International Food Research Journal, 2013;20(2):799-804.
MyJurnal

Consumption of dietary fibre-rich food has been associated with various beneficial physiological properties and health effects. Presently, different types of natural fibre-rich ingredients are added into variety of bakery-based products to improve it fibre content for health promotional purposes. However, majority of these products are frequently added with imported dietary fibre ingredients. In the present study, bread samples were prepared with Zea mays ear (young corn) powder at the levels of either 2%, 4% or 6%. The bread samples were analyzed for nutritional composition, textural properties and sensory acceptance. Addition of young corn powder (YCP) at the level of 6% increases total dietary fibre (from 3.48% to 5.26%), moisture (from 25.64% to 26.55%), fat (from 4.35% to 4.61%) and protein content (from 9.13% to 9.51%) significantly. However, with the increasing of YCP levels in the bread, the carbohydrate content was decreased significantly (from 59.93% to 58.34%) while the ash content (from 0.95% to 0.99%) was not significantly affected. Results of texture profile analysis indicated that addition of YCP up to 6% not significantly affected the springiness (1.01-1.00) but significantly decreased cohesiveness (0.95-0.82). However, the addition of YCP up to 6% has increased hardness (0.18kg-0.57kg), gumminess (0.17kg-0.47kg) and chewiness (0.18kg-0.47kg) attributes of bread samples. On the other result, the sensory evaluation shows that the flavour score was not significantly affected by addition of YCP up to 4% (4.82-4.52) while the tenderness (4.53-4.42), elasticity (4.75-4.58), aroma (4.40-4.47), colour (4.93-4.55) and overall acceptance (4.80-4.35) scores were not significant affected up to 6%. In summary, breads with 4% addition of YCP were considered to be acceptable and potentially used in improving nutritional composition without changing sensory score.

Matched MeSH terms: Hardness
Experimental and theoretical approach on the optical properties of zinc borotellurite glass doped with dysprosium oxide

Halimah MK, Ami Hazlin MN, Muhammad FD

Spectrochim Acta A Mol Biomol Spectrosc, 2018 Apr 15;195:128-135.
PMID: 29414569 DOI: 10.1016/j.saa.2017.12.054

A series of glass samples with chemical formula {[(TeO2)0.7(B2O3)0.3]0.7(ZnO)0.3}1-x(Dy2O3)xwhere x=0.01, 0.02, 0.03, 0.04 and 0.05M fraction were synthesized through conventional melt-quenching method. The most common way to fabricate a glass material is by fusion of two or more component oxides followed by their quenching. This technique is known as melt-quenching technique. Kaur et al. (2016) [1] highlighted that the melt-quenching method able to enhance the mechanical properties like hardness and flexural strength of the material. The nature of the glass systems is proven to be amorphous based on the XRD pattern. The FTIR spectra of the glass systems confirm the existence of five bands which are assigned for the BO4, BO3,TeO4and TeO3vibrational groups. The density of the glass systems is increased with the addition of Dy2O3while the molar volume is found to be inversely proportional to the density of the proposed glass. The optical properties of the glasses are determined through the absorption spectra obtained from the UV-VIS spectrophotometer. From the absorption spectra, the indirect and direct optical band gaps and the Urbach energy are found to be inversely proportional to each other. As the molar fraction of the Dy2O3increased, the optical band gaps are observed to increase as opposed to the Urbach energy. For this glass system, the values of refractive index, electronic polarizability, oxide ion polarizability and the optical basicity are found to decrease as the addition of the dysprosium oxide is increased. From the emission spectra, two intense blue and yellow emission bands are observed, which correspond to the4F9/2→6H15/2and4F9/2→6H13/2transitions of Dy3+ions respectively. The CIE chromaticity coordinates of the zinc borotellurite glass systems are found to be located in the white light region.

Matched MeSH terms: Hardness
Fulltext Degradation effects of dietary solvents on microhardness and inorganic elements of computer-aided design/computer-aided manufacturing dental composites

Munusamy SM, Helen-Ng LC, Farook MS

BMC Oral Health, 2024 Feb 01;24(1):162.
PMID: 38302972 DOI: 10.1186/s12903-024-03905-7

BACKGROUND: Computer-aided design/computer-aided manufacturing (CAD/CAM) dental composites were introduced with superior mechanical properties than conventional dental composites. However, little is known on effects of dietary solvents on microhardness or inorganic elemental composition of CAD/CAM composites.
OBJECTIVES: The objectives of this study were to evaluate the degradation effects of each dietary solvent on the microhardness of the different CAD/CAM dental composites and to observe the degradation effects of dietary solvent on the inorganic elements of the dental composites investigated.
METHODS: Fifty specimens with dimensions 12 mm x 14 mm x 1.5 mm were prepared for direct composite (Filtek Z350 XT [FZ]), indirect composite (Shofu Ceramage [CM]), and three CAD/CAM composites (Lava Ultimate [LU], Cerasmart [CS], and Vita Enamic [VE]). The specimens were randomly divided into 5 groups (n = 10) and conditioned for 1-week at 37°C in the following: air (control), distilled water, 0.02 N citric acid, 0.02 N lactic acid and 50% ethanol-water solution. Subsequently, the specimens were subjected to microhardness test (KHN) using Knoop hardness indenter. Air (control) and representative postconditioning specimens with the lowest mean KHN value for each material were analyzed using energy dispersive X-ray spectroscopy (EDX). Statistical analysis was done using one-way ANOVA and post hoc Bonferroni test at a significance level of p = 0.05.
RESULTS: Mean KHN values ranged from 39.7 ± 2.7 kg/mm2 for FZ conditioned in 50% ethanol-water solution to 79.2 ± 3.4 kg/mm2 for VE conditioned in air (control). With exception to LU, significant differences were observed between materials and dietary solvents for other dental composites investigated. EDX showed stable peaks of the inorganic elements between air (control) and representative postconditioning specimens.
CONCLUSIONS: The microhardness of dental composites was significantly affected by dietary solvents, except for one CAD/CAM composite [LU]. However, no changes were observed in the inorganic elemental composition of dental composites between air (control) and 1-week postconditioning.

Matched MeSH terms: Hardness
Fulltext Thermal Aging Rheological Behavior of Magnetorheological Elastomers Based on Silicone Rubber

Aziz SAA, Mazlan SA, Ubaidillah U, Mohamad N, Choi SB, Che Aziz MA, et al.

Int J Mol Sci, 2020 Nov 27;21(23).
PMID: 33260840 DOI: 10.3390/ijms21239007

Engineering rubber composites have been widely used as main components in many fields including vehicle engineering and biomedical applications. However, when a rubber composite surface area is exposed to heat or sunlight and over a long-term accelerated exposure and lifecycle of test, the rubber becomes hard, thus influencing the mechanical and rheological behavior of the materials. Therefore, in this study, the deterioration of rheological characteristics particularly the phase shift angle (δ) of silicone rubber (SR) based magnetorheological elastomer (MRE) is investigated under the effect of thermal aging. SR-MRE with 60 wt% of CIPs is fabricated and subjected to a continuous temperature of 100 °C for 72 h. The characterization of SR-MRE before and after thermal aging related to hardness, micrograph, and rheological properties are characterized using low vacuum scanning electron microscopy (LV-SEM) and a rheometer, respectively. The results demonstrated that the morphological analysis has a rough surface and more voids occurred after the thermal aging. The hardness and the weight of the SR-MRE before and after thermal aging were slightly different. Nonetheless, the thermo-rheological results showed that the stress-strain behavior have changed the phase-shift angle (δ) of SR-MRE particularly at a high strain. Moreover, the complex mechanism of SR-MRE before and after thermal aging can be observed through the changes of the 'in-rubber structure' under rheological properties. Finally, the relationship between the phase-shift angle (δ) and the in-rubber structure due to thermal aging are discussed thoroughly which led to a better understanding of the thermo-rheological behavior of SR-MRE.

Matched MeSH terms: Hardness
Fulltext Effect of multipath laser shock processing on microhardness, surface roughness, and wear resistance of 2024-T3 Al alloy

Kadhim A, Salim ET, Fayadh SM, Al-Amiery AA, Kadhum AA, Mohamad AB

ScientificWorldJournal, 2014;2014:490951.
PMID: 24737973 DOI: 10.1155/2014/490951

Laser shock processing (LSP) is an innovative surface treatment technique with high peak power, short pulse, and cold hardening for strengthening metal materials. LSP is based on the application of a high intensity pulsed laser beam (I > 1 GW/cm(2); t < 50 ns) at the interface between the metallic target and the surrounding medium (a transparent confining material, normally water) forcing a sudden vaporization of the metallic surface into a high temperature and density plasma that immediately develops inducing a shock wave propagating into the material. The shock wave induces plastic deformation and a residual stress distribution in the target material. In this paper we study the increase of microhardness and surface roughness with the increase of laser pulse energy in 2024-T3 Al alloy. The influence of the thickness of the confining layer (water) on microhardness and surface roughness is also studied. In addition, the effect of LSP treatment with best conditions on wear behaviors of the alloy was investigated.

Matched MeSH terms: Hardness/radiation effects
Biomechanical characterisation of ovine spinal facet joint cartilage

Abd Latif MJ, Jin Z, Wilcox RK

J Biomech, 2012 May 11;45(8):1346-52.
PMID: 22483055 DOI: 10.1016/j.jbiomech.2012.03.015

The spinal facet joints are known to be an important component in the kinematics and the load transmission of the spine. The articular cartilage in the facet joint is prone to degenerative changes which lead to back pain and treatments for the condition have had limited long term success. There is currently a lack of information on the basic biomechanical properties of the facet joint cartilage which is needed to develop tissue substitution or regenerative interventions. In the present study, the thickness and biphasic properties of ovine facet cartilage were determined using a combination of indentation tests and computational modelling. The equilibrium biphasic Young's modulus and permeability were derived to be 0.76±0.35 MPa and 1.61±1.10×10⁻¹⁵ m⁴/(Ns) respectively, which were within the range of cartilage properties characterised from the human synovial joints. The average thickness of the ovine facet cartilage was 0.52±0.10 mm, which was measured using a needle indentation test. These properties could potentially be used for the development of substitution or tissue engineering interventions and for computational modelling of the facet joint. Furthermore, the developed method to characterise the facet cartilage could be used for other animals or human donors.

Matched MeSH terms: Hardness/physiology
Some flexural properties of a nylon denture base polymer

Yunus N, Rashid AA, Azmi LL, Abu-Hassan MI

J Oral Rehabil, 2005 Jan;32(1):65-71.
PMID: 15634304

Nylon denture base material could be a useful alternative to poly (methyl methacrylate) (PMMA) in special circumstances such as patient allergy to the monomer. The aim of this study was to evaluate the flexural properties of a nylon denture base material (Lucitone FRS), a conventional compression-moulded heat-polymerized (Meliodent), a compression-moulded microwave-polymerized (Acron MC) and an injection-moulded microwave-polymerized (Lucitone 199) PMMA polymers. The effect of aldehyde-free, oxygen releasing disinfectant solution (Perform) on these properties was also investigated. The flexural modulus and the flexural strength were assessed with a three-point bending test. Specimens were stored in water at a temperature of 37 degrees C for 30 days. For each material, half of the prepared specimens were randomly selected and immersed in the disinfectant 24 h prior to testing. Results were compared statistically at a confidence level of 95%. The result showed that in both the control and disinfected groups, the flexural modulus of nylon was significantly lower than the three PMMA polymers. The flexural strength of nylon was significantly lower than those of Meliodent and Acron MC but was comparable with Lucitone 199. A 24-h immersion in the disinfecting solution increased the rigidity of nylon denture base material.

Matched MeSH terms: Hardness/drug effects
Characterisation of micro-sized and nano-sized tungsten oxide-epoxy composites for radiation shielding of diagnostic X-rays

Azman NZ, Siddiqui SA, Low IM

Mater Sci Eng C Mater Biol Appl, 2013 Dec 1;33(8):4952-7.
PMID: 24094209 DOI: 10.1016/j.msec.2013.08.023

Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2-10 vol% WO3 loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10-40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO3-epoxy composites in the energy range of 10-25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30-40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO3-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25-49 kV) were in the range of 15-25 keV. Similarly, for a radiology unit operating at 40-60 kV, the equivalent energy range was 25-40 keV, and for operating voltages greater than 60 kV (i.e., 70-100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO3 loading resulted in deterioration of flexural strength, modulus and hardness.

Matched MeSH terms: Hardness
Classification, processing and application of hydrogels: A review

Ullah F, Othman MB, Javed F, Ahmad Z, Md Akil H

Mater Sci Eng C Mater Biol Appl, 2015 Dec 1;57:414-33.
PMID: 26354282 DOI: 10.1016/j.msec.2015.07.053

This article aims to review the literature concerning the choice of selectivity for hydrogels based on classification, application and processing. Super porous hydrogels (SPHs) and superabsorbent polymers (SAPs) represent an innovative category of recent generation highlighted as an ideal mould system for the study of solution-dependent phenomena. Hydrogels, also termed as smart and/or hungry networks, are currently subject of considerable scientific research due to their potential in hi-tech applications in the biomedical, pharmaceutical, biotechnology, bioseparation, biosensor, agriculture, oil recovery and cosmetics fields. Smart hydrogels display a significant physiochemical change in response to small changes in the surroundings. However, such changes are reversible; therefore, the hydrogels are capable of returning to its initial state after a reaction as soon as the trigger is removed.

Matched MeSH terms: Hardness
GEP-based method to formulate adhesion strength and hardness of Nb PVD coated on Ti-6Al-7Nb aimed at developing mixed oxide nanotubular arrays

Rafieerad AR, Bushroa AR, Nasiri-Tabrizi B, Fallahpour A, Vadivelu J, Musa SN, et al.

J Mech Behav Biomed Mater, 2016 08;61:182-196.
PMID: 26874249 DOI: 10.1016/j.jmbbm.2016.01.028

PVD process as a thin film coating method is highly applicable for both metallic and ceramic materials, which is faced with the necessity of choosing the correct parameters to achieve optimal results. In the present study, a GEP-based model for the first time was proposed as a safe and accurate method to predict the adhesion strength and hardness of the Nb PVD coated aimed at growing the mixed oxide nanotubular arrays on Ti67. Here, the training and testing analysis were executed for both adhesion strength and hardness. The optimum parameter combination for the scratch adhesion strength and micro hardness was determined by the maximum mean S/N ratio, which was 350W, 20 sccm, and a DC bias of 90V. Results showed that the values calculated in the training and testing in GEP model were very close to the actual experiments designed by Taguchi. The as-sputtered Nb coating with highest adhesion strength and microhardness was electrochemically anodized at 20V for 4h. From the FESEM images and EDS results of the annealed sample, a thick layer of bone-like apatite was formed on the sample surface after soaking in SBF for 10 days, which can be connected to the development of a highly ordered nanotube arrays. This novel approach provides an outline for the future design of nanostructured coatings for a wide range of applications.

Matched MeSH terms: Hardness
Characterization and fat migration of palm kernel stearin as affected by addition of desiccated coconut used as base filling centre in dark chocolate

Ali A, Selamat J, Man YB, Suria AM

Int J Food Sci Nutr, 2001 May;52(3):251-61.
PMID: 11400474

The characterization and fat migration of palm kernel stearin (PKS) and desiccated coconut, used as base filling centre in dark chocolate were studied. C36 and C38 triglycerides of PKS decreased by 11% and 9.6% respectively, whereas C32 and C34 increased by 97% and 48% respectively. The change in the triglycerides composition of PKS shift the melting point of PKS from 33.2 to 31.4 degrees C. Solid fat content (SFC) of PK reduced by 40% at 30 degrees C. The rate of fat migration was very slow at 18 degrees C storage compared to 30 degrees C. The rate of change of C36 in the chocolate layer was 0.1% week-1 and 1.2% week-1 at 18 and 30 degrees C respectively. Chocolate stored at 18 degrees C showed post hardening during storage period and withstood bloom during the storage period, whereas that stored at 30 degrees C became soft and bloomed faster after 3 weeks of storage.

Matched MeSH terms: Hardness
Chemical, physical and sensory properties of chicken frankfurters substituted with palm fats

Tan SS, Aminah A, Mohd Suria Affandi Y, Atil O, Babji AS

Int J Food Sci Nutr, 2001 Jan;52(1):91-8.
PMID: 11225183

Physico-chemical and sensory characteristics of frankfurters prepared with three types of palm fats (PF60: 40, PF70: 30 and PF80: 20) and palm olein (POo) at 20 and 25% of fat levels were studied. Incorporation of different fats at 20 and 25% did not affect the cooking yields of the frankfurters. Frankfurters incorporated with 25% POo showed the highest value of water-holding capacity (WHC) among eight formulations. The frankfurters containing POo showed the least cooking loss compared to those with palm fats. The incorporation of different type and level of fats resulted in significant changes in the colour (lightness, redness, yellowness) of frankfurters. Texture profiles of both raw and cooked frankfurters were found to be altered by the blending of different type and level of fats. In raw frankfurters, hardness for frankfurters mixed with palm fats were significantly higher than the one with POo but greater values for cohesiveness was observed in raw frankfurters blended with POo. Lowest chewiness was demonstrated by frankfurters mixed with 20% POo. Grilling increased the hardness values of all frankfurters. Contrary to the raw counterparts, cooked frankfurter with POo was the hardest among all formulations. Cohesiveness and chewiness was also found to be significantly higher for cooked frankfurters mixed with POo. Raw frankfurters with fat content of 25% showed greater value in hardness than those of 20%. However, there were no significant differences (P > 0.05) observed for all the texture profile attributes in cooked frankfurters due to fat levels. In sensory evaluation, frankfurters prepared with POo were found to be most acceptable by consumer panels as they scored the highest for hardness rating, chicken flavour, oiliness and overall acceptance attributes.

Matched MeSH terms: Hardness
Investigation into mechanical, absorption and swelling behaviour of hemp/sisal fibre reinforced bioepoxy hybrid composites: Effects of stacking sequences

Thiagamani SMK, Krishnasamy S, Muthukumar C, Tengsuthiwat J, Nagarajan R, Siengchin S, et al.

Int J Biol Macromol, 2019 Nov 01;140:637-646.
PMID: 31437507 DOI: 10.1016/j.ijbiomac.2019.08.166

This work focuses on the fabrication of hybrid bio-composites using green epoxy as the matrix material, hemp (H) and sisal (S) fibre mats as the reinforcements. The hybrid composite with sisal/hemp fibres were fabricated by cost effective hand lay-up technique, followed by hot press with different stacking sequences. Static properties of the composites such as tensile, compressive, inter-laminar shear strengths (ILSS) and hardness were examined. The physical properties such as density, void content, water absorption and thickness swelling were also analyzed. The experimental results indicate that hybrid composites exhibited minor variation in tensile strength when the stacking sequence was altered. The hybrid composite with the intercalated arrangement (HSHS) exhibited the highest tensile modulus when compared with the other hybrid counterparts. Hybrid composites (SHHS and HSSH) offered 40% higher values of compressive strength than the other layering arrangements. HHHH sample exhibited the highest ILSS value of 4.08 MPa. Typical failure characteristics of the short beam test such as inter-laminar shear cracks in the transverse direction, micro-buckling and fibre rupture were also observed.

Matched MeSH terms: Hardness
Fulltext A New Empirical Model for Viscosity of Sulfonated Polyacrylamide Polymers

Akbari S, Mahmood SM, Ghaedi H, Al-Hajri S

Polymers (Basel), 2019 Jun 14;11(6).
PMID: 31207965 DOI: 10.3390/polym11061046

Copolymers of acrylamide with the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid-known as sulfonated polyacrylamide polymers-had been shown to produce very promising results in the enhancement of oil recovery, particularly in polymer flooding. The aim of this work is to develop an empirical model through the use of a design of experiments (DOE) approach for bulk viscosity of these copolymers as a function of polymer characteristics (i.e., sulfonation degree and molecular weight), oil reservoir conditions (i.e., temperature, formation brine salinity and hardness) and field operational variables (i.e., polymer concentration, shear rate and aging time). The data required for the non-linear regression analysis were generated from 120 planned experimental runs, which had used the Box-Behnken construct from the typical Response Surface Methodology (RSM) design. The data were collected during rheological experiments and the model that was constructed had been proven to be acceptable with the Adjusted R-Squared value of 0.9624. Apart from showing the polymer concentration as being the most important factor in the determination of polymer solution viscosity, the evaluation of the model terms as well as the Sobol sensitivity analysis had also shown a considerable interaction between the process parameters. As such, the proposed viscosity model can be suitably applied to the optimization of the polymer solution properties for the polymer flooding process and the prediction of the rheological data required for polymer flood simulators.

Matched MeSH terms: Hardness
Fulltext Recent Progress on Stability and Thermo-Physical Properties of Mono and Hybrid towards Green Nanofluids

Zainon SNM, Azmi WH

Micromachines (Basel), 2021 Feb 11;12(2).
PMID: 33670250 DOI: 10.3390/mi12020176

Many studies have shown the remarkable enhancement of thermo-physical properties with the addition of a small quantity of nanoparticles into conventional fluids. However, the long-term stability of the nanofluids, which plays a significant role in enhancing these properties, is hard to achieve, thus limiting the performance of the heat transfer fluids in practical applications. The present paper attempts to highlight various approaches used by researchers in improving and evaluating the stability of thermal fluids and thoroughly explores various factors that contribute to the enhancement of the thermo-physical properties of mono, hybrid, and green nanofluids. There are various methods to maintain the stability of nanofluids, but this paper particularly focuses on the sonication process, pH modification, and the use of surfactant. In addition, the common techniques to evaluate the stability of nanofluids are undertaken by using visual observation, TEM, FESEM, XRD, zeta potential analysis, and UV-Vis spectroscopy. Prior investigations revealed that the type of nanoparticle, particle volume concentration, size and shape of particles, temperature, and base fluids highly influence the thermo-physical properties of nanofluids. In conclusion, this paper summarized the findings and strategies to enhance the stability and factors affecting the thermal conductivity and dynamic viscosity of mono and hybrid of nanofluids towards green nanofluids.

Matched MeSH terms: Hardness
Fulltext Effect of Aging, Antioxidant, and Mono- and Divalent Ions at High Temperature on the Rheology of New Polyacrylamide-Based Co-Polymers

Akbari S, Mahmood SM, Tan IM, Ling OL, Ghaedi H

Polymers (Basel), 2017 Oct 04;9(10).
PMID: 30965788 DOI: 10.3390/polym9100480

The viscosity of four new polymers was investigated for the effect of aging at high temperature, with varying degrees of salinity and hardness. The four sulfonated based polyacrylamide co-polymers were FLOCOMB C7035; AN132 VHM; SUPERPUSHER SAV55; and THERMOASSOCIATIF copolymers. All polymer samples were aged at 80 °C for varying times (from zero to at least 90 days) with and without isobutyl alcohol (IBA) as an antioxidant. To see the effect of divalent ions on the polymer solution viscosity, parallel experiments were performed in a mixture of CaCl₂-NaCl of the same ionic strength as 5 wt % NaCl. The polymers without IBA showed severe viscosity reduction after aging for 90 days in both types of preparation (5 wt % NaCl or CaCl₂-NaCl). In the presence of IBA, viscosity was increased when aging time was increased for 5 wt % NaCl. In CaCl₂-NaCl, on the other hand, a viscosity reduction was observed as aging time was increased. This behavior was observed for all polymers except AN132 VHM.

Matched MeSH terms: Hardness
Fulltext Assessment of Polyacrylamide Based Co-Polymers Enhanced by Functional Group Modifications with Regards to Salinity and Hardness

Akbari S, Mahmood SM, Tan IM, Ghaedi H, Ling OL

Polymers (Basel), 2017 Nov 27;9(12).
PMID: 30965947 DOI: 10.3390/polym9120647

This research aims to test four new polymers for their stability under high salinity/high hardness conditions for their possible use in polymer flooding to improve oil recovery from hydrocarbon reservoirs. The four sulfonated based polyacrylamide co-polymers were FLOCOMB C7035; SUPERPUSHER SAV55; THERMOASSOCIATIF; and AN132 VHM which are basically sulfonated polyacrylamide copolymers of AM (acrylamide) with AMPS (2-Acrylamido-2-Methylpropane Sulfonate). AN132 VHM has a molecular weight of 9⁻11 million Daltons with 32 mol % degree of sulfonation. SUPERPUSHER SAV55 mainly has about 35 mol % sulfonation degree and a molecular weight of 9⁻11 million Daltons. FLOCOMB C7035, in addition, has undergone post-hydrolysis step to increase polydispersity and molecular weight above 18 million Daltons but it has a sulfonation degree much lower than 32 mol %. THERMOASSOCIATIF has a molecular weight lower than 12 million Daltons and a medium sulfonation degree of around 32 mol %, and also contains LCST (lower critical solution temperature) type block, which is responsible for its thermoassociative characteristics. This paper discusses the rheological behavior of these polymers in aqueous solutions (100⁻4500 ppm) with NaCl (0.1⁻10 wt %) measured at 25 °C. The effect of hardness was investigated by preparing a CaCl₂-NaCl solution of same ionic strength as the 5 wt % of NaCl. In summary, it can be concluded that the rheological behavior of the newly modified co-polymers was in general agreement to the existing polymers, except that THERMOASSOCIATIF polymers showed unique behavior, which could possibly make them a better candidate for enhanced oil recovery (EOR) application in high salinity conditions. The other three polymers, on the other hand, are better candidates for EOR applications in reservoirs containing high divalent ions. These results are expected to be helpful in selecting and screening the polymers for an EOR application.

Matched MeSH terms: Hardness

Filters

Please provide feedback to Administrator (afdal@afpm.org.my)

External Links