Increase In Pore Density Research Articles

Numerical investigation on the influence of porous media structural parameters on pool boiling heat transfer performance

This work investigates pool boiling heat transfer (BHT) and bubble dynamics from a porous medium. The influence of the porous media structural parameters, such as porosity, pore density, porous medium height, thermal conductivity, and wettability, are mainly investigated. The findings indicate that the presence of porous media can increase the critical heat flux (CHF) by an average of 3.75 times and the BHT coefficient by an average of 3.84 times when porosity varies between 57.5% and 98.0% as compared to the plain surface. It is also found that both the CHF and BHT coefficient increase as the porosity decreases if porosity ε≥71.4%. However, they drop with the porosity decreases if porosity ε≤71.4%. On the other hand, the number of nucleation sites, heat transfer area, and bubble escape resistance increase as pore density increases. In addition, increasing the porous media height may enhance BHT performance, but too high a porous media increases the bubble escape resistance and restricts the separation of bubbles. Moreover, the CHF value and the maximum BHT coefficient increase with the thermal conductivity of porous media linearly. Finally, the stronger the wettability, the faster the bubble detachment, and the stronger the BHT performance.

Experimental investigation on the stability and heat transfer enhancement of phase change materials composited with nanoparticles and metal foams

Conventional phase change materials (PCMs) possess the challenge of low thermal conductivity, which hinders the energy exchange rate and storage efficiency. PCMs composited nanoparticles and metal foams have been a proven solution to enhance the thermal characteristics of PCMs. In this work, three enhanced PCM composites including nanoparticle/paraffin, metal-foam/paraffin and nanoparticle/metal-foam/paraffin were prepared using fusion blending and vacuum impregnation method. The effects of different nanoparticles with different mass fractions on the stability and heat storage and release characteristics of nanoparticle/paraffin were investigated. Compared with paraffin, the melting time and solidification time of nano-metal/paraffin are reduced by a maximum of 30.18 % and 43.15 %, respectively. In addition, the effect of pore density of metal foam on natural convective heat transfer process was evaluated. The results showed that the stability in descending order is as follows: nano‑aluminum, nano‑copper and nano‑silver. The optimal mass fraction of nanoparticles with good stability was 1.5 wt% (copper), 1.0 wt% (silver), 1.5 wt% (aluminum), respectively. The metal foam makes the internal temperature distribution of PCMs more uniform in the heat transfer process, while inhibiting the convective heat transfer process. With the increase of pore density, the effect on natural convection heat transfer process rises. When the PPI (pores per linear inch) of foamed metal is greater than 40, the natural convection process can be inhibited, obviously. The foam metal has a more significant effect on the heat transfer performance of nanoparticle/metal-foam/paraffin than that of the nanoparticles. The economic benefits of nanoparticle/paraffin, metal-foam/paraffin and nanoparticle and metal foam composite phase change materials are progressively decrease, with MFP being suitable for applications with high economic budgets.

Thermal-hydraulic performance of a plate heat exchanger with grooved copper foam

This study proposes a plate heat exchanger (PHE) partially filled with metal foam having checkered pattern grooves. The study presents new experimental data obtained from PHE with grooved copper foam that elucidates the effect of mass flux, copper foam groove width, and pore density on the heat transfer coefficient (HTC) and pressure drop (ΔP). The testing is conducted with a water mass flux ranging from 120 to 320 kg/m2s, a groove width ranging from 2 to 6 mm, and a pore density of 30 pores per inch (PPI) and 50 PPI. The results demonstrate that HTC and ΔP increase as the copper foam groove width is reduced. Considering the impact of copper foam groove width on the filling rate, the HTC ratio increases significantly at a filling rate between 50 and 75%. Furthermore, an increase in pore density enhances HTC and ΔP. The plate heat exchanger inserted with copper foam (PHE_CF) provides the optimum thermal-hydraulic performance (TP). However, at a low Reynolds number, the results show that TP of PHE with grooved copper foam with a groove width of 2 mm is similar to PHE_CF. New correlations are also proposed to predict ΔP and HTC in the practical applications.

Effect of enhancement in metal foam pore density on heat transfer of phase-change materials

To explore the effect of metal foam(MF)pore density on the melting and heat transfer of phase-change materials(PCMs), a semi-cylindrical visualization experimental setup was established to experimentally study copper MFs with different pore densities coupled with paraffin wax. The results showed that as pore density increases, the melting time of the composite PCMs decreases compared to that of pure paraffin wax by 11.5%, 16.2% and 18.1% for pore densities of 5, 20, and 30 PPI, respectively. Composite PCMs with a pore density of 30 PPI exhibited fastest melting and lowest maximum temperature difference during melting. Considering the relative thermal energy storage(TES) capacity and relative TES rate, composite PCMs with a pore density of 30 PPI exhibited optimal overall thermal storage performance. Furthermore, heat conduction was the primary means of thermal transmission during the melting of the bottom paraffin. However, the melting of the upper paraffin was nevertheless influenced by natural convection, Hence, as pore size decreased, the influence on the weakening of natural convection became more significant. The results of the study provide guidance for the optimal design of latent heat storage devices for semi-cylinders.

Effects of combined porous media on quenching and re-ignition characteristics of methane/air premixed combustion in a duct

During the study of foam metal suppression of methane combustion in ducts, it was found that under certain conditions, after the flame is extinguished, a re-ignition phenomenon occurs in the area upstream of the foam metal. In this paper, the process and mechanism for the occurrence of this phenomenon were investigated. The porous media used in the experiments is a two-layer structure consisting of a combination of iron-nickel foam and copper foam and was mounted in a transversal position. Each layer of foam metal has a thickness of 5 mm and a pore size of 20 or 40 holes pores per inch (ppi). The results show that flame extinguishment and re-ignition are highly dependent on the material and pore density of the porous media used. After the flame was quenched by the combination of iron-nickel foam with the same pore density of 40ppi, the re-ignition intensity was higher (a dazzling white light could be observed) and the flame area was larger. However, when a combination of iron-nickel foam with different pore densities was used, the re-ignition intensity, flame oscillation frequency and amplitude were significantly lower. However, both re-ignition flames can last for a long time. In addition, the incorporation of copper foam with high thermal conductivity resulted in the decay of flame propagation speed and the overpressure before and after quenching increased significantly with the increase of pore density of the first layer of iron-nickel foam.

Thermal Performance Analysis of Gradient Porosity Aluminium Foam Heat Sink for Air-Cooling Battery Thermal Management System

The three dimensional thermal model of a forced air-cooling battery thermal management system (BTMS) using aluminium foam heat sink (AFHS) is established, and the effects of porosity, pore density, and mass flow rate on the thermal and flow performance are discussed numerically from the aspects of pressure drop and temperature control effectiveness. The results reveal that an AFHS can markedly reduce the battery temperature compared with the BTMS without AFHS, but it also causes huge pressure loss and increases the temperature difference between the upstream and downstream of the battery. Reducing the porosity of aluminium foam reduces the battery’s average temperature, but increases the temperature difference. The increase of pore density leads to the increase of pressure drop, but has little effect on the battery temperature. Based on this, a study of the gradient porosity of the AFHS is carried out, and the thermal and flow performance are compared with the homogeneous AFHS. The results show that the AFHS with porosity-increasing gradient pattern (PIGP) in the direction perpendicular to flow reduces the pressure loss and improves flow performance. The AFHS with a porosity-decreasing gradient pattern (PDGP) in the flow direction has no obvious effect on the flow characteristics, but it can reduce the temperature difference of the battery. The direction of gradient porosity can be selected according to need. In addition, due to the energy absorption characteristics of aluminium foam, AFHS can improve the crashworthiness of the battery pack. Therefore, AFHS has great potential in air-cooled BTM.

Enhanced transmembrane transport of reactive oxygen species by electroporation effect of plasma

AbstractRecently, plasma has been proposed as a new efficient tool for various biological and medical applications. The function of plasma is mainly realized through two aspects: Electric field and reactive species. However, because the interactions between plasma and cells are quite complicated, the synergistic effect of electric field and reactive species has not been studied in depth. In this paper, the synergetic effects of electric field and transportation of reactive species on cells are investigated by a two‐dimensional finite element model. The exposure of cells to plasma results in the sufficiently high transmembrane voltage (1 V) and electroporation. When the electric field of plasma is less than 104 V/cm, the radius of nanopores generated by plasma increases with the electric field. The further increase of electric field to 105 V/cm does not cause a significant increase of nanopore radius, whereas the pore density increases by five times. The increase of discharge frequency significantly decreases the time needed to generate stable nanopores. The nanopores enhance the diffusion of H2O2 generated by plasma through the cell membrane significantly. Compared with the reality that H2O2 does not freely diffuse across cell membranes, the “generation and enhanced transportation” effect will further expand the application range of plasma medicine.

Experimental Evaluation and Modeling of Air Heating in a Ceramic Foam Volumetric Absorber by Effective Parameters

Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer by acting as a support for the reactive materials. Heating these absorbers with highly inhomogeneous concentrate irradiation induces high thermal gradients that affect their thermal performance. Owing to the critical function of these component in the reactor, it is necessary to define a selection criterion for the foam-type absorbers. In this work, we performed an experimental and numerical thermal analysis of three partially stabilized zirconia (PSZ) foam-type absorbers with pore density of 10, 20, and 30 PPI (pores per inch) used as a volumetric absorber. A numerical model and an analytical approximation were developed to reproduce experimental results, and calculate the thermal conductivity, as well as volumetric heat transfer coefficient. The results show that an increase in pore density leads to an increase in the temperature difference between the irradiated face and the rear face of the absorber, this occurs because when pore density increases the concentrated energy no longer penetrates in the deepest space of the absorber and energy is absorbed in areas close to the surface; therefore, temperature gradients are created within the porous medium. The opposite effect occurs when the airflow rate increases; the temperature gradient between the irradiated face and the rear face is reduced. This behavior is more noticeable at low pore densities, but at high pore densities, the effect is less relevant because the internal structure of porous absorbers with high pore density is more complex, which offers obstructions or physical barriers to airflow and thermal barriers to heat transfer. When the steady state is reached, the temperature difference between the two faces of the absorber remains constant if the concentrate irradiation changes slightly, even changing the airflow rate. The results obtained in this work allow us to establish a selection criterion for porous absorbers that operate within solar reactors; this criterion is based on knowledge of the physical properties of the porous absorber, the environment, the working conditions, and the results expected.

Frequency-dependent analysis of ultrasound apparent absorption coefficient in multiple scattering porous media: application to cortical bone

The effect of matrix viscoelastic absorption on frequency-dependent attenuation in porous structures mimicking simplified cortical bone is addressed in this numerical study. An apparent absorption is defined to quantify the difference between total attenuation (resulting from both absorption and scattering) and attenuation exclusively due to scattering. A power-law model is then used to describe the frequency-dependent apparent absorption as a function of pore diameter and density. The frequency response of the porous structures to a Gaussian pulse is studied to determine the frequency range over which the system can be considered linear. The results show that for low scattering regimes (normalized frequency 0.80), the system and its apparent absorption can be considered linear. Hence, the total attenuation coefficient results from the summation of scattering and absorption coefficients. However, for highly scattering regimes, the system can no longer be considered linear, as the apparent absorption vs. frequency deviates from a linear trend. As the pore density increases, the apparent absorption coefficient increases as well.

Tunable Biodegradable Polylactide-Silk Fibroin Scaffolds Fabricated by a Solvent-Free Pressure-Controllable Foaming Technology.

Polylactide (PLA) and silk fibroin (SF) are biocompatible green macromolecular materials with tunable structures and properties. In this study, microporous PLA/SF composites were fabricated under different pressures by a green solid solvent-free foaming technology. Scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and Fourier transform infrared (FTIR) spectroscopy were used to analyze the morphology, structure, and mechanical properties of the PLA/SF scaffolds. The crystalline, mobile amorphous phases and rigid amorphous phases in PLA/SF composites were calculated to further understand their structure-property relations. It was found that an increase in pore density and a decrease in pore size can be achieved by increasing the saturation pressure during the foaming process. In addition, changes in the microcellular structure provided PLA/SF scaffolds with better thermal stability, tunable biodegradation rates, and mechanical properties. FTIR and XRD analysis indicated strong hydrogen bonds were formed between PLA and SF molecules, which can be tuned by changing the foaming pressure. The composite scaffolds have good cell compatibility and are conducive to cell adhesion and growth, suggesting that PLA/SF microporous scaffolds could be used as three-dimensional (3-D) biomaterials with a wide range of applications.

Facile preparation of Poly(butylene succinate)/Carbon nanotubes/polytetrafluoroethylene ternary nanocomposite foams with superior electrical conductivity by synergistic effect of “ball milling” and supercritical fluid-Assisted processing

Conductive polymer composites (CPCs) with different types of polytetrafluoroethylene (PTFE) were prepared via melt mixing, and the cellular structure was introduced into poly (butylene succinate) (PBS) by the supercritical CO2 foaming technique. The carbon nanotubes (CNTs) had the best dispersion in the PBS/CNTs/PTFE-P5 composite (PTFE with a diameter of approximately 5–10 μm). The CNTs enhanced the crystallizability of PBS, and the addition of PTFE was more significant, especially PTFE-P5. The storage modulus increased, and a transition from liquid-like to solid-like behavior occurred at low frequencies. Adding PTFE dramatically improved the pore structure, leading to a two-orders-of-magnitude increase in pore density, especially for PTFE-P5. The conductivity (δ) of solid PBS/CNTs/PTFE-P5 was four times higher than that of PBS/CNTs. The δ values of all the foams were much higher than those of their solid counterparts, demonstrating that the introduction of a large number of pores optimized the dispersion of CNTs and further improved the electrical conductivity because of the formation of a more complete conductive network structure (CNS). In particular, the δ value of foamed PBS/CNTs/PTFE-P5 under 3 wt% CNT loading reached 54.05 S/m. The thermal and mechanical properties, as well as the thermal conductivity, were also investigated. This work provides a simple method to prepare flexible biodegradable CPCs with a highly dispersed CNT CNS under high melt viscosity conditions.

Incorporation of a novel Ag–Cu@ZIF-8@GO nanocomposite into polyethersulfone membrane for fouling and bacterial resistance

A series of nanocomposite membranes, Ag@ZIF-8@GO/PES, Cu@ZIF-8@GO/PES and Ag–Cu@ZIF-8@GO/PES, were fabricated via phase inversion method. These were characterized using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDS), X-ray photoelectron microscopy (XPS), atomic force microscopy (AFM) and water contact angle (WCA) measurements. The SEM images revealed an increase in pore density with the incorporation of the hydrophilic GO, porous ZIF-8 and the ZIF-8@GO composite as well as those containing Ag and Cu. The presence and the distribution of the nanoparticles onto the membranes were confirmed by XPS, EDS and elemental mapping. The composite membranes containing AgNPs showed excellent antibacterial properties against Escherichia coli. Furthermore, the antifouling properties of the composite membranes were assessed by filtration of bovine serum albumin (BSA), as a model foulant. An increased flux recovery ratio for the composite membranes (78–97%) was observed in comparison to that of the pristine PES membrane (43%). The flux recovery ratios of the nanocomposite membranes were maintained for more than six cycles showing their recyclability and fouling resistance. The observed metal leaching from the composite membranes was minimal and far less than the WHO threshold. The incorporation of the composite fillers led to concurrent improvement in the bacterial growth inhibition and protein fouling resistance boding well for application in water treatment.

Adsorption of methylene blue on chemically modified lychee seed biochar: Dynamic, equilibrium, and thermodynamic study

Contamination of drinking water due to methylene blue (MB) dye is a severe health hazard. In the present work, biochar from lychee seed was synthesized by chemical activation of KOH and used for the abatement of MB dye from aqueous solution. The chemical, morphological, and textural properties of the biochar were characterized using FTIR, RAMAN, Zeta potential, XRD, SEM, FESEM, and N2 sorption isotherm. The SEM and FESEM images clearly showed the increase in pore density after activating with KOH, further supported by the N2 sorption isotherm analysis. The batch adsorption experiment was carried out to determine the optimum conditions for MB dye adsorption. The adsorption process followed Langmuir isotherm and Pseudo second order kinetic model well with maximum Langmuir adsorption capacity of 124.5 mg g−1 at room temperature. The detailed kinetic study proposed that intraparticle diffusion is not only the rate determining step, but the chemical interaction or external mass transfer also influences the adsorption process. XPS spectra, before and after adsorption confirmed the definite interaction of MB dye onto the biochar. The mechanism for adsorption on MLS was evaluated and ascribed to electrostatic interaction, pi-pi interaction, and hydrogen bonding interaction. The thermodynamic study showed that the adsorption was endothermic and spontaneous. The above results showed that the biochar could be effectively used as a low-cost adsorbent for the removal of MB dyes from aqueous solutions.

Experimental Study on the Thermal Performance of a Finned Metal Foam Heat Sink with Phase Change Material

The present research conducts an experimental study on the thermal performance of the finned metal foam (FMF) heat sinks with phase change material. The dynamic temperature response of an FMF heat sink is analyzed and compared with the corresponding finned heat sink. The effects of porosity and pore density on the thermal performance of FMF heat sinks are analyzed. Furthermore, the enhancement ratio and heat exchange capability are evaluated for the optimization of FMF heat sinks. The results indicate that the thermal conduction enhancement caused by the addition of metal foam exceeds the heat transfer loss arising from the suppression of natural convection. A decrease in porosity leads to an increase in heat exchange capability and contributes to a higher enhancement ratio. Considering the tradeoff between the low operating temperature and longer duration of reliability, the porosity of 0.9 is the best choice for FMF heat sinks. Though the porosity is identical, the thermal performance of an FMF heat sink is better with the increase of pore density. Considering the maximum energy charging capacities are identical, the FMF heat sink with larger pore density is recommended for practical engineering applications.

An experimental and numerical investigation of forced convection in high porosity aluminum foams subjected to jet array impingement in channel-flow

This paper reports an experimental and numerical investigation on flow and thermal transport in high porosity aluminum foams (ε~0.94–0.96) placed in a channel of square cross-section and subjected to jet array (5 × 5) impingement. The plate issuing the jets was flushed with the metal foam face. Experiments were conducted for three different values of jet-to-jet spacing (x/dj=y/dj) of 2, 3 and 5, and three foam samples with pore-densities 10, 20, and 40 PPI (pores per inch). Values of steady-state heat transfer rate and pressure drop were calculated for Reynolds number (based on channel hydraulic diameter and channel inlet velocity) ranging from 2500 to 13,500. The main findings are as follows: first, for all the test runs, the impingement configurations had higher heat transfer rate, h, compared to that for the baseline configuration of metal foams in a channel flow. Second, for all values of the jet-to-jet spacing, an increase in pore-density was accompanied by an increase in heat transfer. The enhancement (h/h0) varied between 26 and 48, with the highest gain observed for the widest jet (x/d=2) and the highest pore density (40 ppi) configuration, where h0 is the heat transfer coefficient for developed turbulent flow in a circular duct. The numerical computations reveal interesting recirculating flow structures immediately downstream of the jet exits and the extent of flow penetrating in the foam. Collectively, these flow patterns play a dominant role in determining the volume of metal foam volume participating in the thermal transport and the net convective heat transfer rate.

Control of pore density on TiO2 nanostructure films: Effect of etchant quantity and anodic voltage

The spatial distribution of pores on a TiO2 nanotube film contribute to its specific surface area, which is a critical factor in applications such as photo-electrochemical water splitting. In this work, we show that while both anodization voltage and etchant quantity determine the TiO2 nanostructure pore density, the quantity of the etchant has a greater effect. We anodized titanium foil substrates, varying either voltage or etchant quantity. With higher voltage, the results show an increase in pore diameters which decreased nanotube density. However, with an increase in etchant quantity, the development of inter-pore voids that create tubular structures, resulted in a remarkable increase in pore density. The study shows that at low quantities of NH4F, the pore density is significantly reduced. Based on these findings, a mechanism of preparing Ti foil templates that could be used to develop spatially distributed nanotubes by multiple-step anodization in ethylene glycol-NH4F electrolytes is proposed.

Thermal hydraulic performance augmentation by high-porosity thin aluminum foams placed in high aspect ratio ducts

High porosity metal foams are known for providing high heat transfer rates, however, the concomitant higher-pressure losses have been a concern towards the realization of enhanced thermal hydraulic performance. Present study aims towards developing metal foam-based cooling configurations subjected to forced convection in a channel by employed very thin and high porosity Aluminum foams, where the goal is to achieve maximum foam volume participation in heat dissipation. To this end, a comprehensive experimental study has been carried out to investigate the effect of foam pore density (pores per inch: PPI) and channel aspect ratio (AR) on the thermal hydraulic performance of thin metal foams. High porosity (93%) thin aluminum foams with pore densities of 5, 20 and 40 PPI were studied, where the convective heat transport was facilitated through air forced through the channel. For the 40 ppi foams, three foam heights of 3.175 mm, 6.35 mm and 19 mm were tested, for 20 ppi foams, two foam heights of 6.35 mm and 19 mm were tested, and for the 5 ppi foams, one height of 19 mm was tested. These three different foam heights yielded in channel ARs of 16:1, 8:1 and 8:3, respectively. Heat transfer gain due to metal foams was evaluated against a geometrically identical smooth channel as well as with the Dittus-Boelter correlation for developed turbulent flow in circular ducts. Experimental data reveals that, for a given AR, an increase in pore-density resulted in both, increase in heat transfer as well as pressure drop. Amongst all three channel configurations, the 40 ppi foams had highest heat transfer, where the gain with respect to smooth channel for Re 5000 was ~21, 12 and 9.5 times, for 8:3, 8:1 and 16:1 channels respectively. Increase in channel AR (thinner foams) demonstrated an increase in heat transfer performance for a given pumping power. The thermal hydraulic trends observed for thin and high pore-density foams proved them to be viable candidates for compact electronics cooling.

Influence of pore density on heat transfer and pressure drop characteristics of wet air in hydrophilic metal foams

To optimize the performance of hydrophilic metal foam, the influence of pore density on heat transfer and pressure drop characteristics of wet air in hydrophilic metal foams is experimentally investigated. The experimental conditions include pore density from 5PPI to 40PPI. The results show that, as pore density increases from 5PPI to 40PPI, the overall heat transfer coefficient of wet air in hydrophilic metal foams always increases at relative humidity of 30–70%, while it initially increases then decreases at relative humidity of 90%, representing a maximum value at PPI of 20; the pressure drops always increase as pore density increases; the best comprehensive performance of hydrophilic metal foam is achieved at PPI of 20. Compared with the uncoated metal foam, the overall heat transfer coefficient of wet air in hydrophilic metal foam is increased by 2–21%, while the pressure drop of wet air in hydrophilic metal foam is decreased by 1–15% at most conditions; the hydrophilic metal foam provides better comprehensive performance than the uncoated metal foam and the hydrophilic fin-and-tube heat exchangers. Correlations for the Colburn j factor and Friction factor f are developed for the wet air flow in hydrophilic metal foams, and the maximal deviation of the correlation for the j and f factors are within ±15% and ±20%, respectively.

Perchloric acid functionalized nano-silica and protic ionic liquid based non-aqueous proton conductive polymer electrolytes

Both protic ionic liquids (PILs) and superacids are known to be rich sources of protons and their good carrier as well. Herein, we report a novel approach in developing non-aqueous proton conductive nanocomposite electrolytes (PCNEs) by making composite of a PIL; diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) and a superacid; perchloric acid (HClO4). Initially, HClO4 was immobilized on nano-silica powders; and then both ([dema][TfO]) and HClO4·SiO2 were incorporated into poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy suggest decrease in overall crystallinity of the composite membranes on addition of [dema][TfO]. Scanning electron microscopy (SEM) images show that microstructures such as spherulite structures and micropores on the membrane surface evolves with [dema][TfO] concentration. At 80 wt% of [dema][TfO], the density of pores appears on the membrane surface is maximum. The dc ionic conductivity is also observed to be increasing with [dema][TfO] concentration. The maximum conductivity of 0.02 mS cm−1 and 0.6 m Scm−1 are achieved at room temperature (30 °C) and 100 °C, respectively for 80 wt% of [dema][TfO]. This ionic conductivity variation is well correlated with the increase in pore density and decreasing crystallinity of the PCNE film.

Synthesis, characterization and antibacterial activity of thymol-loaded polylactic acid microparticles entrapped with essential oils of varying viscosity

Double emulsion technique (W1/O/W2) was used to achieve PLA (polylactic acid)-based microparticles loaded with thymol (hydrophilic antibacterial active) with high encapsulation efficiency (> 90%) that was later released in water in controlled fashion. In order to enhance the release of thymol from semicrystalline slow degrading PLA matrix, pores were introduced into the particles by incorporating minute quantity of essential oils (EOs) such as castor, mustard, olive and coconut oils of varying viscosity (from 128 to 13 mPa S). Strikingly, it was found that the pore size of microparticles (pore size 1.2–0.53 µm and specific surface area 7.5–2.1 m2/g) has been influenced by the viscosity of EOs. The plausible mechanism of formation of pores using EOs was also explored. As expected, the release rate of thymol did get accelerate with the increase in pore density and its release mechanism can well be explained with the help of power law model. In addition to that, these porous particles were demonstrated to act as an effective carrier for continuous delivery of thymol with enhanced inhibitory activity probably due to synergistic action of EOs and thymol. Therefore, EOs employed here served dual purposes. These PLA-based microparticles composed of completely natural ingredients can be exploited as active food packaging material to prolong the shelf life of food.