Molded Sheets Research Articles

Evolution of the cavity structure of HDPE/UHMWPE blends during cold stretching

AbstractThe cavitation process of high‐performance HDPE/UHMWPE blends with a uniform dispersion of UHMWPE during cold stretching was investigated. It was observed that incorporating a small amount of UHMWPE into the HDPE matrix resin can serve as a nucleating agent, increasing the number of contact sites and accelerating the crystallization rate. This leads to the formation of thicker lamellar crystals and tethered molecules, ultimately enhancing the mechanical properties of the HDPE matrix. Furthermore, the relationship between the natural tensile ratio and strain‐hardening modulus was confirmed. Microstructural changes within the blends were also explored. As the drawing tangles in the middle, the cavities subsequently evolve by collapsing and merging to align parallel to the tensile direction, culminating in tensile damage forming a large crack in the final macroscopic form. As a result, the presence of more tethered molecules in the later stages of stretching inhibits further cavity growth.Highlights The HDPE/UHMWPE blends were prepared by solution blending and ultrasound‐assisted twin‐screw extrusion. The mechanisms underlying the formation and evolution of cavities in HDPE/UHMWPE blends, which lead to stress whitening during tensile damage, were examined by using DSC and SAXS/WAXD. The relationship between microstructure and mechanical properties was analyzed by cold‐drawing the molded blended sheets at room temperature.

Development of rice starch/recycled polypropylene biocomposites with jute waste nanofiber-based filler

The current investigation deals with the synthesis of rice starch and jute nanofiber (JNF) and its dispersion into recycled Polypropylene (PP) matrix. The morphological and spectral analysis of the fabricated jute nanofiber revealed that the produced fibers are crystalline and are elliptical in shape with diameter of 20 nm. The developed compression moulded sheets with different composition of jute nanofiber (2%) and rice starch (0 - 50%) were vigorously analyzed to determine the effect of fillers on the structural (SEM, XRD), compositional (FTIR), thermal (DSC, TGA, MFI) and optical (Haze, Transmittance) properties. Mechanical property assessment revealed that there is a continuous increase in Young’s modulus (YM) and stiffness (ST) with increase in starch content from 0 to 50% from 1250.8 MPa to 101107.7 N/m to 2130.5 MPa and 172210.3 N/m respectively indicating the enhancement in toughness with increase in biofiller. The decrease in Tensile strength (TS) and elongation at break (EB) from 34.31 MPa to 6.5% (0% starch) to 12.74 MPa and 1.62% (50% starch in matrix) respectively indicates the loosening of internal polymer chains which thereby indicates susceptibility of the sheets towards faster deterioration in natural environment. The enhanced crystalline sample RCPP1(containing 20% rice starch, 2% JNF) was considered as the best sample having 15.21 MPa (TS), 2.5% (EB), 1357.5 MPa (YM), 103942.7 N/m (ST). Hence, the synthesized composite matrix consisting of recycled PP along with starch laden jute nanofiber could be a viable biogenic material option for effective application in packaging industries.

Influence of intraoral conditions on the accuracy of digital and conventional implant impression techniques for two-implant-supported fixed dental prostheses.

To compare the trueness and precision of different impression techniques for two-implant-supported fixed dental prostheses between extraoral and intraoral conditions at different locations. Six volunteers participated in this study. A resin block with two parallel analogs was fabricated as an implant site simulator (ISS). The ISS was bonded to a molded ethylene vinyl acetate sheet to create a reference model. For each participant, four reference models were prepared based on the locations of the ISSs: maxillary posterior/anterior region (MaxP/MaxA) and mandibular posterior/anterior region (ManP/ManA). Five impressions were taken extraorally using the open-tray (conventional implant impression technique, CIT) and intraoral scanning (digital implant impression technique, DIT) techniques. The reference models were positioned in the participants' mouths, and impressions were obtained intraorally using the CIT and DIT. The interanalog distance (d) and angulation (θ) were measured to calculate trueness (Δd, Δθ) and precision (dP, θP). Two-way ANOVA and t tests were performed (α=0.05). For the DIT, under intraoral conditions, the Δd and Δθ in MaxP and Δθ in ManP were significantly higher than those under extraoral conditions. For the CIT, under intraoral conditions, the Δd and Δθ in ManA and ManP and Δθ in MaxP were significantly lower than those under extraoral conditions. No significant differences in the dP and θP of either DIT or CIT were observed between the two conditions. Intraoral conditions affected the trueness of DIT and CIT in different regions but had no influence on precision.

Interfacial Surface Properties of Compression Moulded Hydrolysed Polyvinyl Acetate (PVAc) Using Different Release Materials

Understanding the effect surface production has on polymer properties is important in the design of advanced materials. The aim of this study was to determine how the moulding process affected the rate of hydrolysis and the topography, chemistry and physicochemistry of PVAc moulded, hydrolysed surfaces. Three different mould surface materials were used to produce compression moulded PVAc sheets which were treated with aqueous NaOH at a range of concentrations. The Textile moulded sheet demonstrated the best hydrolysis results. The topography of the moulded sheets was transferred to the surfaces and the Kapton release sheet was visually smooth at lower magnification and demonstrated some pitting at higher magnification. The Teflon surface had features transferred from the coated stainless steel at lower magnifications and linear features at higher magnifications and the textile surface had a wrinkled appearance and irregularly spaced peaks. The release sheet used to mould the PVAc surfaces, affected the physicochemical parameters. The Kapton moulded surface demonstrated the most polar attributes and the Teflon surface the most dispersive. It was clear that the selection of the mould material had an influence on surface properties and hydrolysis of moulded PVAc. Such information is important for engineering design in industrial processes.

Comparative Analysis of Compression Molded Products of Recycled Waste Poly(Vinyl Chloride) and Virgin Poly(Vinyl Chloride) Fill Material

Waste poly(vinyl chloride) fill material from the cooling tower of a power plant was used for mechanical recycling. Mechanical recycling is the processing of plastic waste without changing the original chemical structure of the plastic. The waste rigid poly(vinyl chloride) fill material was cleaned, grinded and compression molded at optimized conditions of time, temperature and pressure using a compression molding machine. Virgin poly(vinyl chloride) was purchased and compression molded by the same compression molding machine. The compression molded sheets of waste poly(vinyl chloride) and virgin poly(vinyl chloride) were characterized by attenuated total reflection Fourier transform infrared analyses, tensile properties analyses, and thermal properties analyses. The results revealed that waste rigid poly(vinyl chloride) fill material is mechanically recyclable into new products such as pipes, profiles, furniture and other related products.

Rheological Behavior and Dynamic Mechanical Properties for Interpretation of Layer Adhesion in FDM 3D Printing.

Commercial filaments of poly(lactic acid) (PLA) composites with particulate filler, carbon fiber, and copper powder with different contents were fabricated by FDM 3D printing in XZ-direction at bed temperatures of 45 °C and 60 °C. The effects of additives and bed temperatures on layer adhesion, fracture behavior, and mechanical performance of the PLA composites 3D printing were evaluated. Rheological properties informed viscous nature of all filaments and interface bonding in the PLA composites, which improved printability and dimensional stability of the 3D printing. Crystallinity of the PLA composites 3D printing increased with increasing bed temperature resulting in an improvement of storage modulus, tensile, and flexural properties. On the contrary, the ductility of the 3D printing was raised when printed at low bed temperature. Dynamic mechanical properties, the degree of entanglement, the adhesion factor, the effectiveness coefficient, the reinforcing efficiency factor, and the Cole–Cole analysis were used to understand the layer adhesion, and the interfacial interaction of the composites as compared to the compression molded sheets. SEM images revealed good adhesion between the additives and the PLA matrix. However, the additives induced faster solidification and showed larger voids in the 3D printing, which indicated lower layer adhesion as compared to neat PLA. It can be noted that the combination of the additives and the optimized 3D printing conditions would be obtain superior mechanical performance even layer adhesion has been restricted.

Three Dimensional Printing of Multiscale Carbon Fiber-Reinforced Polymer Composites Containing Graphene or Carbon Nanotubes.

Three-dimensional printing offers a promising, challenging opportunity to manufacture component parts with ad hoc designed composite materials. In this study, the novelty of the research is the production of multiscale composites by means of a solvent-free process based on melt compounding of acrylonitrile–butadiene–styrene (ABS), with various amounts of microfillers, i.e., milled (M) carbon fibers (CFs) and nanofillers, i.e., carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). The compounded materials were processed into compression molded sheets and into extruded filaments. The latter were then used to print fused filament fabrication (FFF) specimens. The multiscale addition of the microfillers inside the ABS matrix caused a notable increase in rigidity and a slight increase in strength. However, it also brought about a significant reduction of the strain at break. Importantly, GNPs addition had a good impact on the rigidity of the materials, whereas CNTs favored/improved the composites’ electrical conductivity. In particular, the addition of this nanofiller was very effective in improving the electrical conductivity compared to pure ABS and micro composites, even with the lowest CNT content. However, the filament extrusion and FFF process led to the creation of voids within the structure, causing a significant loss of mechanical properties and a slight improvement of the electrical conductivity of the printed multiscale composites. Selective parameters have been presented for the comparison and selection of compositions of multiscale nanocomposites.

Tensile, rheological and morphological characterizations of multi-walled carbon nanotube/polypropylene composites prepared by microinjection and compression molding

Abstract Polypropylene (PP) reinforced with 2 and 4 wt% of multi-walled carbon nanotubes (MWNT) were melt-blended in twin screw extruder and then molded by compression or micromolding process. The impact of injection speed on the surface morphology, rheological and tensile characteristics was investigated by using a scanning electron microscope, parallel plate rheometry, and tensiometry. Results showed that the tensile properties of micro-molded specimens were remarkably higher than those of the compression molded sheets. Compared to compression molded sheets, micromolded specimens demonstrated up to 40 and 244% higher tensile stiffness and yield strength, respectively, most likely due to the alignment of polymer chain segments in the flow direction induced during the micromolding process. It was observed that the fast filling speed caused a drop in the tensile properties of the nanocomposites and polymer. Rheological examination revealed that the presence of a rheological percolation network in the nanocomposites produced by micromolding and the fast injection speed was beneficial for establishing the percolated network. Morphological examination revealed that the size of nanotube agglomerations that appeared in micromolded specimens was up to five times smaller than in compression molded sheets and the agglomeration size decreased with the increase of the injection speed.

Disordered graphite platelets in polypropylene (PP) matrix by spherical alumina particles: Increased thermal conductivity of the PP/flake graphite composites

The strategy of filler hybriding has been widely used to enhance the thermal or electrical conductivities of polymer composites. Flake graphite (FG) has a very high thermal conductivity, but the flaky structure makes it prone to generate planar orientation in polymer matrix during melt processing. This inevitably leads to significant difference in thermal conductivities along the in-plane and through-plane directions of molded sheet samples. The arrangement of FG in parallel induces the limited thermal conductivity along the vertical direction and this poses a great limitation for the real application. In this work, spherical alumina (Al2O3) was introduced into the highly filled (≥30 wt%) polypropylene (PP)/FG composites. It was found that a small content of alumina replacing the FG significantly increases the thermal conductivity on the through-plane direction of the sheet samples. The analysis indicated that spherical alumina particles effectively destroyed the orderly alignment of graphite platelets in the matrix, especially in the composites with high FG loadings. More interconnection between the FG platelets was therefore achieved on the thickness direction of the composites and the composites exhibited enhanced thermal conductivity along the through-plane direction. This work endows a new strategy for composites with two-dimensional functional fillers to improve the vertical thermal conductivity.

Effect of Valley Beater Refining on Tensile Properties of Molded Pulps from Rice Straws

Rice straw, an abundant agricultural waste, is shown to be a promising resource for pulp and paper packaging manufacturing. In this study, rice straw pulps or cellulose fibers were extracted using a soda-AQ process and then the rice straw pulp slurries were refined by a Valley beater. The effect of refining time (15-60 min) on the pulp fiber characteristics was studied. It was found that both initial fiber length and width were decreased with refining time. The refined fibers became fibrillated, finer, and also more uniform in size confirmed by SEM. The pulp freeness (CSF) was reduced with increasing refining time as expected due to higher water-holding capacity of more fibrillated pulps. Then, the molded sheets were formed from the prepared rice straw pulps and examined. From tensile testing, the results indicated that the tensile properties of the molded sheets from the refined pulps were significantly enhanced (p < 0.05), thanks to an increase in fibrillated fiber surface area and inter-fiber bonding degree. The Valley beater refined rice straw pulp provided the molded sheet with the highest tensile index of 51.96 ± 4.08 Nm/g which are comparable to that of the sheets prepared from PFI mill refining process. The tensile properties of the current refined sheets were also in the acceptable range for typical commercial molded pulp packaging. In addition, the freeness values of the optimal Valley beater refined pulps are relatively high (348-423 ml), implying a benefit in forming process and manufacturing of pulp products.

Investigation of tensile behavior and molecular structure of the thermoplastic polyurethane sheets injection molded at different mold temperatures

AbstractThis paper aims to investigate the influence of the mold temperature on the mechanical responses at different ambient temperature and molecular structure of the injection molded TPU sheets. The tensile properties of the TPU sheets prepared at different mold temperatures were obtained at different ambient temperatures. As the mold temperature increases, both the elongation at break and tensile strength of the specimens increase. The specimens show yield behavior during stretching at −30 and −50°C. The microstructure of the TPU sheets was characterized by DMA, AFM, and birefringence. The results show that the higher mold temperature can reduce the aggregation of hard domains because of the higher mobility of the hard segments. In‐situ SAXS and WAXS measurements were carried out at −30°C test temperature to exhibit the evolution of the microstructure during stretching. When the specimens are prepared at 40°C mold temperature, the hard domains are destroyed and difficult to orient along the stretching direction. In contrast, the hard domains begin to be deformed and oriented along the stretching direction above the yield strain when the specimens molded at higher mold temperature. The above microstructure evolution is consistent with the tensile behavior of the TPU specimens.

Direct Resinification of Konjac Glucomannan via Hot-Press Compression Molding

Hot-press compression molding was used to resinify a renewable source-derived linear 1,4-linked β-D-glucan copolymer, i.e., konjac glucomannan (KGM), via the generation of reactive aldehyde groups that tend to crosslink with hydroxyl groups of the glucans. The optimal molding temperature was found to be around 170 °C, with keeping the pressure at 20 MPa for 3.5 min and controlling the water content of the starting KGM powder to be around 22%. The molded KGM resin sheets were found to be crystallized in the annealed KGM polymorph form. Dynamic mechanical analysis revealed that the softening initiation temperature of the KGM resin was ca. 100 °C due to an onset of an increase in the loss modulus, E’’. The representative KGM resin sheets obtained under the optimal molding conditions were transparent, colored brown, and exhibited a tensile strength of 20.8 ± 4.5 MPa, Young’s modulus of 2.2 ± 0.3 GPa and elongation at break of 1.1 ± 0.2%.

The Impact of Plastic pH on Silicone Elastomer Compression Set

<div class="section abstract"><div class="htmlview paragraph">Sealing applications in electrified vehicle powertrains present a unique set of boundary conditions when contrasted with typical transmission or internal combustion engine applications, including changes in fluidic exposure, operating pressure, temperature profiles, etc. This novel powertrain environment opens the gasket material spectrum to elastomers uncommon in standard powertrain joints, which allows for more optimized, higher-value sealing solutions. However, this also introduces new risks, including the risk of excessive compression set in silicone elastomers due to acidity in adjacent plastics (which can result from shifting to non-halogenated flame retardants from halogenated flame retardants). To understand this phenomenon, compression set testing was conducted with plastic resins ranging from pH = 3.4 to pH = 7.3 and three high-consistency rubber (HCR) silicone elastomers. For each silicone, compression set was plotted linearly against concentration of hydrogen ions ([H+]) in the plastic and plotted exponentially against plastic pH. This produced a regression model relating compression set in the elastomer to acidity of the adjacent plastic. Then, a threshold pH value - after which the plastic begins to significantly increase compression set in the silicone - was determined by overlaying silicone-only compression set results with the silicone + plastic regression model. The resulting threshold value given the associated conditioning was a pH of 4.5 for all three silicone samples tested, indicating that a plastic resin accelerates compression set in the neighboring silicone if the plastic has a pH ≤ 4.5. Studies into the impact of (1) plastic sample form factor (raw material pellets, colorized material pellets, or molded plastic sheets) and (2) time on plastic pH were evaluated; both showed no statistical impact on pH measurements. Overall, this effect is believed to be due to acid-induced cleavage of the siloxane bond, which causes depolymerization in the silicone by breaking the backbone chain, thereby resulting in gasket compression set.</div></div>

Tailoring nanofibrillated cellulose through sonication and its potential use in molded pulp packaging

Nanofibrillated cellulose (NFC) was systematically tailored by ultrasonic-assisted esterification with lactic acid at different amplitudes and times, which led to modified NFC (mNFC) with different degrees of substitution (DS), between 0.21 and 0.55, as confirmed by titration, FTIR, and C13 NMR. A partial fragmentation and decrease in crystallinity of mNFC were revealed by TEM and XRD. To form molded pulp sheets, 5 wt% mNFC was added into a bagasse (BG) pulp slurry, then partially dewatered before hot-pressed. mNFC worked effectively as self-retention aid, partly solving the issue of drainage during sheet forming as commonly observed from unmodified NFC. The BG/mNFC (DS 0.55) sheet exhibited an enhancement in tensile properties. Water resistance and barrier performance of the current sheets were also evidently increased. The results suggested that the higher DS on mNFC can improve water resistance and mechanical properties, simultaneously overcoming drainage challenges in processing of molded pulp products.

On the effective elastic properties based on mean-field homogenization of sheet molding compound composites

Fiber reinforced polymers, for example sheet molding compounds (SMC), have gained significant importance as lightweight materials. In this work, a SMC composite based on unsaturated polyester-polyurethane hybrid resin (UPPH) reinforced with discontinuous long glass fibers is considered. The mechanical behavior of this composite is highly governed by its microstructure. Based on samples extracted from compression molded sheets, the underlying microstructure is characterized by means of X-ray computed tomography (µCT) scans. Tensile tests are performed to investigate and characterize the elastic properties of this composite. A mean-field method is presented to approximate the effective elastic behavior. In this context, the tensile tests performed serve as validation data for the simulation results. The effective Young’s modulus is in good agreement with the experimentally obtained data with a deviation less than 15%.

Portable digital drape meter with a unique sensor-based measurement system

Measurement of draping behaviour of cloth/soft moulded sheet is carried out using ammonia- based instrument. The measurement requires much time, and human intervention. So, measurement of draping behaviour is unpopular, though, it is a most important property parameter in fashion industry. In the present work, a desk top type automatic digital drape meter with a unique sensor-based measurement system has been developed. The measurement time could be reduced to 5.0 min as compared to 180–210 min for conventional system. Human intervention has been completely eliminated for data acquisition and processing. Calculated value of draping behaviour is displayed digitally. The instrument is ergonomically designed and no chemical is required. Weight of the instrument is 16.0 kg. The fabrication cost of the instrument was US $ 3,200.00 only.

Hydroxylated Natural Rubber Effect on Crystallinity and Mechanical Properties of PLA

This work focuses on the effect of functionality of hydroxylated natural rubber (HNR) and its loading on crystallinity and mechanical properties of polylactic acid (PLA). HNR with hydroxyl groups of 9.09% by mole was prepared from natural rubber latex via epoxidation reaction and then the epoxy rings were cleavaged to produce the hydroxyl groups by using heating at the temperature of 70 °C. HNR4 with the hydroxyl groups of 15.25% by mole was prepared from ONR4 latex with M̅n of 3.94 × 103 g/mol and M̅w of 5.06 × 103 g/mol. PLA was then blended with the obtained HNR or HNR4 with different weight ratios of PLA:HNR = 70:30 and 60:40. It was found that hydroxylated natural rubber increased the crystallinity of molded PLA sheet from 7.54% to 18.20% for molded PLA:HNR = 70:30 sheet, to 25.16% for molded PLA:HNR = 60:40 sheet and to 24.38% for molded PLA:HNR4 = 70:30 sheet. Morphological analyses revealed the appearance of co-continuous phase in the molded PLA:HNR4 = 70:30 clearer than the molded PLA:HNR = 60:40 and molded PLA:HNR = 70:30 sheets. As a result, it clarified that the higher functionality of hydroxyl groups based on lowering the molecular-weight enhanced the compatibility between PLA and HNR. On the other hand, the mechanical properties of PLA:HNR4 = 70:30 were found to be the highest tensile strength (14.46 MPa), elongation at break (13.62%) and modulus (4.10 MPa) though PLA:HNR = 60:40 gave the highest impact strength of 163.98 J/m. This was believed that the hydroxylated natural rubber enhanced the crystallinity and impact strength of PLA through the interface interaction and/or chemical bonds between hydroxyl groups of HNR and carboxyl terminal groups of PLA.

Comparative study of the extrinsic properties of poly(lactic acid)-based biocomposites filled with talc versus sustainable biocarbon.

This study investigates the effects talc and two sizes of biocarbon have as fillers in a PLA bioplastic, when considering them for durable composite applications. Analysis of the PLA-based biocomposites' resistance to wear and flammability accompanied by the vapor barrier characteristics were conducted, with subsequent rheological and thermal properties to further explain the observed results. The compression molded sheets showed a reduction in abrasion by greater than 69% for either filler type compared to the neat PLA due to their high stiffness. In contrast, only the talc provided barrier properties that hindered both water and oxygen permeability, while biocarbon did not possess a high aspect ratio to form a tortuous path necessary for barrier improvement. Yet, the biocarbon-filled PLA biocomposites provided superior flammability resistance due to its char-like caricature that superseded the neat PLA and talc variant which both failed the horizontal burning test. The rheology of the composites provided evidence in the degradation of the PLA chains from the presence of the biocarbon that did not occur with the talc, which may have also contributed to the lower barrier and higher burn resistance from increased dripping. Thus, both talc and biocarbon have their own potential applicability when it comes to acting as a barrier enhancer or flammability retardant due to their intrinsic nature, but both possess wear reinforcement for focus in the tribological area.

Enhancing the dispersion and adhesion of short aramid fibers in bromo‐isobutylene‐isoprene rubber using maleated polybutadiene resin via co‐vulcanization with 4, 4’ bis(maleimido)diphenylmethane

Composites based on brominated isobutylene‐isoprene rubber (BIIR) and 5‐mm short aramid fiber were prepared by varying the fiber content from 1 to 10 phr using 4, 4’ bismaleimido diphenyl methane (BMDM) and zinc oxide as the vulcanizing agent. Morphological analysis revealed that the fiber dispersion becomes inferior even at 5 phr loading due to fibrillation during mixing. As a result, the 10 phr fiber‐filled composite showed a brittle failure under a tensile deformation. To solve this problem, maleic anhydride‐grafted polybutadiene (MA‐g‐PB) resin was treated with the aramid fibers in the 1:1 ratio prior to mixing with the rubber matrix. Excellent fiber dispersion could be seen in both the visual image of the molded sheet and the scanning electron microscope image of the fractured surface. The stress–strain curve of the 10 phr fiber‐filled composite after the resin treatment showed a tough deformation behavior with a breaking elongation >100% indicating an enhanced fiber‐matrix adhesion. From the vulcanization studies of the fiber‐filled BIIR before and after the MA‐g‐PB resin treatment, it has been identified that a co‐crosslinking reaction between the MA‐g‐PB‐treated fiber and the BIIR matrix with BMDM via Alder‐ene and Diels‐Alder reactions is responsible for the enhanced fiber–matrix adhesion. POLYM. COMPOS., 40:2993–3004, 2019. © 2018 Society of Plastics Engineers

Obtaining antimicrobial bilayer starch and polyester-blend films with carvacrol

Bilayer films using polyester blends (P) and starch (S) were obtained and characterized, incorporating carvacrol as active compound. Carvacrol was incorporated by spraying it between melt blended and compression moulded sheets or through its incorporation into the chloroform P solution used to obtain P cast films. Different PLA-PHBV ratios (75:25 and 65:35) were tested, with and without 15 wt% of PEG1000, whereas the 75:25 ratio with PEG was only used for cast sheets, based on its better overall properties. Mono and bilayers were characterized as to their tensile and water vapour barrier properties and thermal behaviour. Release kinetics of carvacrol in different food simulants and in in vitro antibacterial activity against Listeria innocua and Escherichia coli were also analysed. Incorporating carvacrol by spraying it between the polyester and starch sheets was not effective at retaining the compound in the bilayers. However, the incorporation of carvacrol into cast P films, and the subsequent formation of bilayers with the S sheets, was highly effective at providing practically total carvacrol retention. These active bilayers exhibited highly improved tensile and water vapour barrier capacity with respect to the S monolayer (87% reduction in WVP, 840% increase in elastic modulus) and inhibited the growth of L. innocua and E. coli from both P or S contact sides of bilayers, depending on the internal diffusion of carvacrol through the bilayer and its adequate release of the compound into the culture medium.