PLA coating improves the performance of renewable adsorbent pads based on cellulosic aerogels from aquatic waste biomass

1 PLA coating improves the performance of renewable adsorbent pads based on cellulosic aerogels from aquatic waste biomass Isaac Benito-Gonzálezab, Amparo López-Rubioa, Laura G. Gómez-Mascaraqueb, Marta Martínez-Sanza* a Food Safety and Preservation Department, IATA-CSIC, Avda. Agustín Escardino 7, 46980 Paterna, Valencia, Spain b Department of Food Chemistry & Technology, Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland *Corresponding author: Tel.: +34 963200022; fax: +34 963636301 E-mail address: [email protected] 2 Abstract Lightweight, hydrophobic, adsorbent pads based on aerogels from different cellulosic and nanocellulosic fractions extracted from Posidonia oceanica waste biomass were developed by a simple freeze-drying and PLA dipping method. The pure (nano)cellulosic aerogels presented highly porous structures, capable of adsorbing large amounts of oil (up to ~34 g oil/g aerogel); however, they lost their integrity when soaked in water. The incorporation of PLA hydrophobized the aerogels and improved significantly their mechanical performance (up to 10-fold increase in the compression stress). The most porous aerogel structures, obtained with the lowest (nano)cellulosic concentrations and with the less purified fractions, incorporated greater amounts of PLA upon dipping, which was mostly distributed filling in the pores. All the PLA-coated (nano)cellulosic aerogels presented a hydrophobic behavior, with contact angles of 95-130º and selectively adsorbing greater amounts of oil (5.9-9.2 g oil/g aerogel) than water (2.8-6.7 g H2O/g aerogel). These materials present a great potential as adsorbent pads for oil spill cleaning and food packaging applications. Keywords: porous materials; Posidonia; seaweed; biopolymers; oil sorption; microstructure. 3 Abbreviations PLA: Poly(lactic acid) F2A: Cellulosic fraction obtained by omitting both Soxhlet and KOH treatments F2: Cellulosic fraction obtained by omitting the KOH treatment F3A: Cellulosic fraction obtained by omitting the Soxhlet treatment F3: Pure cellulose fraction NANO F2A: Nanocrystals obtained from F2A NANO F2: Nanocrystals obtained from F2 NANO F3A: Nanocrystals obtained from F3A NANO F3: Nanocrystals obtained from F3 4 1. Introduction The large increase in population over the last century, together with the globalization of the markets and the consumerist society have generated a significant increase on the demand of goods and services. As a result, large amounts of residues are generated worldwide, being plastic materials one of the most abundant residues. Synthetic plastics are widely used nowadays due to their excellent mechanical performance, cost-efficiency and high chemical stability. Although the latter attribute can benefit the use of synthetic plastics in certain applications, such as food packaging (to protect the products from the external environment and extend their shelf life), it also gives rise to severe environmental issues. These materials require extremely long times to disintegrate after their disposal into landfills. Moreover, they can reach marine ecosystems, where they are transformed into the so-called micro-plastics, which are not only a great hazard to aquatic organisms [1], but can also be incorporated into the food chain, posing a threat to human health [2, 3]. In this context, circular economy policies, aiming to reduce waste through the whole production chain by the utilization of alternative natural bio-based raw materials and the application of re-valorization strategies, are currently being boosted by European governments. Not only alternative renewable resources are being studied to replace less environmentally friendly materials, but also greener processes, reducing the use of chemicals and energy, are being explored to minimize the environmental impact of the manufacturing chain. In the particular case of the food packaging sector, biopolymers, i.e. bio-based and biodegradable polymers, are being extensively explored for the replacement of synthetic plastics in several types of packaging structures such as trays, lids and sorbent pads [4, 5]. Each type of packaging structure needs to meet certain specific requirements and, thus, the 5 properties of biopolymers have to be adapted accordingly. For instance, sorbent pads are commonly used in packages to minimize the amount of excess liquids released by fresh products upon storage, although they can also be utilized as templates for the incorporation and sustained release of bioactive compounds towards the food products [6, 7]. Aerogels are extremely light and porous materials with high surface area and low density, which are useful for environmental, construction, pharmaceutical, bio-medical, food and cosmetic applications due to their high absorption and adsorption capacities [8-10]. Although aerogels have been traditionally made from inorganic materials such as silica or alumina [11, 12], their application as pads in the food packaging area requires the search of sustainable materials with properties that resemble those from the commercially used synthetic polymeric pads. In this sense, aerogels made from biopolymers such as cellulose, pectin or chitin have been recently proposed as promising materials [13]. In particular, many recent works reporting on the production of cellulose-based aerogels can be found in the literature [14-16]. Despite their great potential, the application of these materials within food packaging is still a largely unexplored area, which is mostly due to the complexity of their manufacturing processes, often involving the use of chemical agents and/or organic solvents unsuitable for food applications, and their poor performance under high relative humidity conditions [6, 17]. Cellulose-based aerogels are typically produced by complex methodologies involving an initial disruption of the crystalline structure to dissolve cellulose (through the use of ionic liquids or mercerization treatments) [16, 18], gelation, cellulose regeneration, solvent exchange and a final drying step by means of supercritical CO2 or freeze-drying [19, 20]. Due to the highly hydrophilic nature of cellulose, the obtained aerogels are susceptible to disintegrate upon moisture contact, thus requiring the application of hydrophobization treatments. These treatments normally consist of chemical modification of cellulose, cross- 6 linking and/or coating with hydrophobic agents such as silanes [14, 21, 22], which are not acceptable for food-related applications and confront the sustainability and circular economy principles. In this work, the valorization of Posidonia oceanica waste biomass for the production of biobased cellulosic and nanocellulosic aerogels is proposed. Previous work has demonstrated that less purified (nano)cellulosic fractions may present superior performance than pure cellulose, while increasing the sustainability of the obtained materials [23]. Based on this, the properties of aerogels produced from different (nano)cellulosic fractions by freeze-drying of their aqueous suspensions have been evaluated. Furthermore, a simple PLA (poly(lactic acid)) dipping method has been tested for the hydrophobization and improvement of the mechanical performance of selected aerogels. The developed materials are therefore fully bio-based, adsorbent systems suitable for food packaging applications and produced by means of a cost-effective and sustainable method. 2. Materials and methods 2.1. Raw materials Biomass waste material consisting of Posidonia oceanica leaves was directly collected in the sea shore of Calpe (Alicante, Spain) in January 2018. The material was washed vigorously with water in order to remove sand and stored under refrigeration (4º C) until its use. 2.2. Preparation of cellulosic fractions and nanocrystals from Posidonia oceanica biomass 7 A purification procedure described in previous works [24, 25] and consisting of a Soxhlet extraction (4 g of dry material were extracted with 800 mL of 2:1 toluene:ethanol for 24 h), followed by bleaching (the material obtained from the first step was treated for 5 h at 70 °C with 700 mL of 1.4% w/v NaClO2) and an alkaline treatment (the material was treated with 400 mL 5% w/v KOH for 24 h at room temperature, followed by 2 h at 90 °C), was applied to sequentially remove cell wall components and obtain holocellulose (F2) and pure cellulose (F3). Less purified fractions were also obtained by omitting the Soxhlet step (F2A and F3A). These fractions were then subjected to an optimized hydrolysis treatment with sulphuric acid, as described in [23], to produce nanocellulosic materials (labelled as NANO F2, NANO F2A, NANO F3 and NANO F3A). Briefly, the fractions were immersed in a H2SO4 solution (30% v/v), with a ratio of 1.5 g (dry fraction) / 100 mL of H2SO4, and were heated to 50 ºC during 2 h under stirring conditions. The obtained fractions and nanocrystals were stored in the fridge as partially hydrated gel-like materials, until further use. 2.3. Production of cellulosic aerogels Aerogels were produced by dispersing the required amount of cellulosic or nanocellulosic materials in 15 mL of distilled water by ultra-turrax homogenization to obtain concentrations of 0.5, 1, 1.5 and 2 wt.-%. These suspensions were transferred to plastic Petri dishes (5 cm diameter), frozen at −80 °C for 4 h and then freeze-dried using a Genesis 35-EL freeze-dryer (Virtis). The obtained cellulosic and nanocellulosic aerogels were labeled according to the fraction used as starting material (F2, F2A, F3, F3A, NANO F2, NANO F2A, NANO F3 and NANO F3A). Additionally, selected aerogels (F3, NANO F3, NANO F2A and NANO F2) were used to produce hybrid cellulosic-PLA aerogels using a proprietary technology [26]. Briefly, PLA 8 was dissolved in chloroform at a fixed concentration of 5% (w/v) by stirring at 50ºC during 30 minutes. The (nano)cellulosic aerogels were dipped in the PLA solution for 1 minute and the samples were then dried at room temperature in a fume hood until the chloroform was completely evaporated (at least 24 h). The obtained aerogels were stored in equilibrated relative humidity cabinets at 0% RH and 25ºC for at least three days prior to their characterization. The amount of PLA sorbed by the aerogels was calculated as follows: % PLA = 𝑊𝑊𝑊𝑊 −𝑊𝑊0 𝑊𝑊0 𝑥𝑥 100 (1) where 𝑊𝑊0 refers to the (nano)cellulosic aerogel initial weight and 𝑊𝑊𝑊𝑊corresponds to the final sample weight (aerogel + PLA). Al least four samples were prepared for each (nano)cellulosic aerogel type. 2.4. Scanning electron microscopy (SEM) SEM was conducted on a Hitachi microscope (Hitachi S-4800) at an accelerating voltage of 10 kV and a working distance of 8-16 mm. Small samples (~5 mm2 area) of the pure (nano)cellulosic and PLA-coated (nano)cellulosic aerogels were cut to observe their surface. The samples were then sputtered with a gold–palladium mixture under vacuum during 3 minutes before their morphology was examined. 2.5. Density of aerogels Aerogel densities were determined from the weight and volume of each individual aerogel. The weight was determined by an analytical balance (Precisa Gravimetrics AG SERIES320XB, Dietikon, Switzerland) and the dimensions were measured by a digital calliper at three different positions. 9 2.6. Water and oil sorption Squared aerogel specimens with a total surface area of 1 cm2 were cut, weighed and immersed in sealed containers containing 15 mL of distilled water or sunflower oil. The samples were periodically taken out of the liquid and weighed after removing the liquid excess. Measurements were taken until the samples were equilibrated and the total weight gain was calculated. After equilibration, the samples were removed from the liquid, placed on top of aluminum foil (in the case of water) and filter paper (in the case of oil) and left drying at ambient conditions. The weight was registered periodically, until it was constant (~1 week). The water and oil retention capacity was calculated from the difference between the weight after drying and the initial weight of the samples, before soaking them in the liquids. All the measurements were carried out at least in triplicate. The experimental curves obtained for the water and oil sorption processes were fitted using pseudo-first order and pseudo-second order models. The pseudo-first order model is described by the following expression: 𝑞𝑞 (𝑡𝑡) = 𝑞𝑞𝑒𝑒 [1− 𝑒𝑒𝑘𝑘1𝑡𝑡] (2) where 𝑞𝑞 (𝑡𝑡) is the amount of adsorbed solute, 𝑞𝑞𝑒𝑒 its value at equilibrium and 𝑘𝑘1 is the pseudofirst order kinetic rate constant. On the other hand, the pseudo-second order model is described by the following expression: 𝑞𝑞 (𝑡𝑡) = 𝑞𝑞𝑒𝑒 𝑘𝑘2 ∗𝑡𝑡 1+𝑘𝑘2 ∗𝑡𝑡 (3) where 𝑘𝑘2 ∗=𝑘𝑘2·𝑞𝑞𝑒𝑒 and 𝑘𝑘2 is the pseudo-second order kinetic rate constant. 16 noted that the most compacted aerogels, especially F2A, displayed the slower oil release kinetics, showing the importance of the aerogel microstructure on the sorption and desorption processes. Overall, the NANO F2 and NANO F2A aerogels seem to be the most promising materials, given their reduced production costs and environmental impact (as compared to the more purified nanocellulosic fractions), their optimal microstructure in terms of porosity and homogeneity and their lightweight characteristics. 3.2. Production of hydrophobic PLA-coated (nano)cellulosic aerogels The poor resistance of the (nano)cellulosic aerogels to high humidity conditions would strongly limit their range of applications. A straightforward methodology based on dipping the (nano)cellulosic aerogels in PLA solutions was evaluated for their hydrophobization and the obtained aerogels were characterized to determine the effect of PLA incorporation on their mechanical performance and sorption capacity. To this end, four aerogels were selected: NANO F2 and NANO F2A (the most optimum in terms of microstructure and sorption capacity) and F3 and NANO F3 (the most purified cellulosic and nanocellulosic fractions). The latter ones were selected to assess the effect of the degree of purification and of the cellulose hydrolysis. Furthermore, four different solid concentrations (0.5, 1, 1.5 and 2 wt.- %) were tested to determine the effect of (nano)cellulose concentration on the morphology, sorption capacity and mechanical integrity of the produced aerogels. The visual aspect and representative SEM images from the obtained aerogels, shown in Figure 2, evidenced that, for a given concentration, the NANO F2 and NANO F2A aerogels presented more porous structures. As expected, increasing concentrations of the (nano)cellulosic fractions led to 17 denser aerogel structures. The density of the aerogels (cf. Table 2) was directly related to their microstructure, being the more porous materials the ones presenting the lowest density values (i.e. NANO F2 and NANO F2A at their lowest concentration). 18 Figure 2. Visual aspect and SEM micrographs of the selected P. oceanica (nano)cellulosic aerogels at four different concentrations. (A) F3, (B) NANO F3, (C) NANO F2A and (D) NANO F2. Scale bars in the SEM micrographs correspond to 1 mm. Table 2. Density of the selected P. oceanica (nano)cellulosic aerogels at the different tested concentrations and of the corresponding PLA-coated (nano)cellulosic aerogels. Different letters show significant differences between the same concentration (column) while * show significant differences between concentrations for the same material (p≤ 0.05). Density (mg/cm3) 0.5% 1% 1.5% 2% F3 42.3 ± 1.3 b 76.1 ± 2.3 b* 98.8 ± 2.8 b** 125.9 ± 5.5 b*** F3 + PLA 118.4 ± 5.8 c 180.6 ± 5.3 c* 197.6 ± 10.0 c* 232.9 ± 15.3 c** 19 NANO F3 38.4 ± 0.3 b 73.8 ± 0.8 b* 97.5 ± 1.2 b** 113.9 ± 3.7 b*** NANO F3 + PLA 109.6 ± 4.3 c 177.0 ± 7.3 c* 188.3 ± 1.9 c* 216.1 ± 12.5 c** NANO F2A 12.8 ± 0.1 a 23.3 ± 0.5 a* 35.1 ± 1.4 a** 46.8 ± 1.8 a*** NANO F2A + PLA 41.6 ± 2.9 b 73.4 ± 4.5 b* 91.3 ± 5.4 b** 112.3 ± 6.6 b*** NANO F2 13.2 ± 0.2 a 25.7 ± 0.3 a* 38.3 ± 0.8 a** 51.6 ± 1.7 a*** NANO F2 + PLA 45.5 ± 4.4 b 77.1 ± 4.3 b* 103.3 ± 6.3 b** 116.1 ± 7.3 b** After dipping the materials into the PLA solutions, the amount of polymer retained by the aerogels was estimated. As deduced from Figure 3, there was a clear tendency of decreasing the PLA incorporation when increasing the (nano)cellulose concentration. Moreover, the less purified aerogels (NANO F2A and NANO F2) were able to retain greater amounts of PLA than the pure cellulose aerogels. Remarkably, NANO F2A and NANO F2 were able to incorporate more than 200% PLA (with regards to their initial weight) when the nanocellulose concentration in the starting aerogels was 0.5-1 wt.-%. These results were consistent with the higher porosity observed in these particular samples (cf. Figure 2). The density values of the obtained PLA-coated (nano)cellulosic aerogels were also estimated and the obtained values are gathered in Table 2. As expected, the incorporation of PLA significantly increased the density of the aerogels, being this effect more remarkable at the lowest (nano)cellulosic concentration (0.5 wt.-%) since the PLA weight gain was greater in that case. The highest absolute density values (110-230 mg/cm3) corresponded to the 2 wt.- % aerogels, which were within the range of those previously reported for bacterial cellulose aerogels reinforced with PLA produced by ethanol precipitation and supercritical CO2 drying (162 mg/cm3) [30]. 20 Figure 3. Amount of PLA incorporated into the P. oceanica (nano)cellulosic aerogels (% with respect to the initial aerogel weight). Different letters denote significant differences between concentrations for the same aerogel type while * show significant differences between different aerogels at the same concentration (p ≤ 0.05). SEM characterization was also carried out to assess the distribution of the PLA phase in the coated (nano)cellulosic aerogels and representative micrographs are shown in Figure 4. As observed, the PLA-coated aerogels presented much more compact and continuous structures than the pristine (nano)cellulosic aerogels. The PLA seemed to be mostly located filling in the pores and also covering the surface of the aerogels in a particular way: PLA created a continuous layer showing a very singular network of micro-holes (diameter ~3 μm) which were particularly visible in the 1.5% and 2% aerogels (see insets in Figure 4). These microholes were most likely originated by the evaporation of chloroform after the PLA dipping process, and therefore they are expected to appear within the PLA-rich regions. 21 22 B 0.5% 1% 1.5% 2% 0.5% 1% 1.5% 2% C 23 Figure 4. SEM images of the PLA-coated (nano)cellulosic aerogels. (A) F3, (B) NANO F3, (C) NANO F2A and (D) NANO F2. Insets represent regions of the aerogels at higher magnification. Since PLA is known to possess a more hydrophobic behaviour than cellulose [31, 32], contact angle measurements were performed on selected aerogels to identify the effect of PLA incorporation on the water affinity of the aerogels’ surface. The coating of the aerogels with PLA had a dramatic effect; while the original (nano)cellulosic aerogels were not even measurable due to the highly hydrophilic nature of these materials [23], the PLA-coated (nano)cellulosic aerogels presented contact angle values between 100º and 125º. Such values are similar to those reported for PLA films [31] and demonstrate the marked 24 hydrophobization effect of the PLA dipping method. Interestingly, the most purified fractions (F3 and NANO F3) showed a more hydrophobic behaviour at the lowest (nano)cellulose concentration (0.5 wt.-%), which was most likely due to the greater amount of PLA incorporated, while this was not the case for the less purified fractions (NANO F2A and NANO F2). These results suggest that in the case of the more porous aerogels PLA was preferentially incorporated into the inner region, filling in the pores. On the other hand, there seemed to be an optimum density range (40-50 mg/cm3, cf. Table 2) for which the PLA was capable of filling the internal pores and the excess polymer was distributed coating the surface of the aerogels, therefore maximizing the hydrophobization effect. Indeed, the most purified aerogels (i.e. F3 and NANO F3) at their lowest concentration (0.5%) and the least purified aerogels (i.e. NANO F2A and NANO F2) at their highest concentration (2%), which presented densities within the “optimum range”, showed the maximum contact angle values, ranging from 110 to 130º. Table 3. Calculated contact angle, water sorption, oil sorption and oil retention capacities for PLA-coated (nano)cellulosic aerogels at their lowest (0.5%) and highest (2%) concentrations. Values followed by different letters are significantly different (p ≤ 0.05). Contact angle (º) Water sorption capacity (g H2O/g aerogel) Oil sorption capacity (g oil/g aerogel) Oil retention capacity (g oil/g aerogel) F3 0.5% + PLA 124.5 ± 9.9 a 3.3 ± 0.1 de 6.9 ± 0.1 f 0.4 ± 0.1 d F3 2% + PLA 100.9 ± 4.6 b 2.8 ± 0.1 e 5.9 ± 0.1 g 3.9 ± 0.5 a NANO F3 0.5% + PLA 127.1 ± 5.6 a 3.7 ± 0.2 cd 8.4 ± 0.1 d 1.2 ± 0.2 c NANO F3 2% + PLA 95.2 ± 8.6 b 2.9 ± 0.1 e 6.1 ± 0.1 g 2.4 ± 0.3 b 25 NANO F2A 0.5% + PLA 101.4 ± 5.7 b 6.7 ± 0.1 a 9.2 ± 0.2 c 0.7 ± 0.1 d NANO F2A 2% + PLA 120.0 ± 3.1 a 4.2 ± 0.1 c 7.6 ± 0.2 e 3.0 ± 0.2 ab NANO F2 0.5% + PLA 107.1 ± 6.5 ab 5.3 ± 0.1 b 8.4 ± 0.1 d 0.8 ± 0.2 cd NANO F2 2%+ PLA 112.3 ± 7.0 ab 3.8 ± 0.1 c 7.3 ± 0.1 ef 2.6 ± 0.3 b The dramatic changes in the microstructure and water affinity of the aerogels induced by the incorporation of PLA were expected to affect their sorption capacity. Thus, water and oil sorption experiments were carried out on the PLA-coated (nano)cellulosic aerogels. Water sorption curves for all the aerogels could be fitted by a pseudo-first order equation, while a pseudo-second order model worked better for the kinetics of oil sorption (cf. Figure S2). All the kinetic parameters obtained from the fitting are compiled in the supplementary material (cf. Table S1). Although the surface of the PLA-coated (nano)cellulosic aerogels showed a hydrophobic behaviour, as suggested by the contact angle measurements, the aerogels were able to adsorb water while also keeping their integrity (unlike the pure (nano)cellulose aerogels). The results from the water sorption/desorption experiments (cf. Figure S3) show that the sorption and desorption processes were relatively fast (with all the samples reaching equilibrium values in ca. 4 h for the sorption and 4-8 h for the desorption), suggesting weak interactions between water and the structure of the aerogels. The aerogels containing the less purified fractions (NANO F2 and NANO F2A) presented the highest water sorption capacities, reaching values up to ca. 500-700% (cf. Table 3). It should also be noted that, for all the aerogel types, lower (nano)cellulosic concentrations produced higher adsorption capacities. These results can be directly related to the microstructure of the aerogels, i.e. a lower degree of purification and lower (nano)cellulosic concentrations gave rise to more porous structures, which were able to adsorb more water. The PLA-coated (nano)cellulosic 32 microstructure: more porous aerogels, capable of incorporating greater amounts of PLA into their structures, were obtained with lower (nano)cellulose concentrations. PLA incorporation led to surface hydrophobization, with all the coated aerogels presenting contact angles of 95130º and being able to keep their integrity when soaked in water. These PLA-coated (nano)cellulosic aerogels were capable of selectively adsorbing greater amounts of oil (5.99.2 g oil/g aerogel) than water (2.8-6.7 g H2O/g aerogel). The sorption capacity of the aerogels was correlated with their microstructure, with the most porous materials being more susceptible to the sorption/desorption of liquid media. The incorporation of PLA led to a substantial increase on the compression stress (up to 10-fold) of the coated aerogels. Moreover, the mechanical performance was also strongly related to the microstructure, being a greater porosity linked to poorer mechanical performance. Overall, the aerogels’ microstructure plays a crucial role on their properties, before and after PLA coating. These results show that the least purified fractions from Posidonia oceanica waste biomass have a great potential to develop fully bio-based, extremely lightweight, hydrophobic and highly adsorbent aerogels with good mechanical properties by using a simple PLA dipping method. These materials represent a greener and more sustainable alternative for the development of adsorbent structures useful in diverse applications, such as oil spill cleaning and food packaging. Acknowledgements This work was financially supported by the project RTI2018-094408-J-I00 from the Spanish Ministry of Science, Innovation and Universities, the “Agencia Estatal de Investigación” and co-funded by the European Union’s Horizon 2020 research and innovation programme 33 (ERA-Net SUSFOOD2). Isaac Benito-Gonzalez was recipient of an Erasmus Plus grant (European programme) from the Polytechnic University of Valencia (UPV) in order to carry out part of the experimental work at Teagasc (Fermoy, Ireland). Supplementary Material Additional Supplementary Material may be found in the online version of this article. Figure S1. Oil sorption and desorption kinetics for the P. oceanica (nano)cellulosic aerogels (0.5 wt.-%). Figure S2. Fitting of the oil and water sorption kinetics for the NANO F2A 0.5% + PLA aerogel using pseudo-first order and pseudo-second order models. Figure S3. Water sorption/desorption kinetics of the different aerogels at their different concentrations. Figure S4. Oil sorption/desorption kinetics of the different aerogels at their different concentrations. Figure S5. SEM images of selected PLA-coated (nano)cellulosic aerogels after the oil desorption experiments. Table S1. Kinetic parameters obtained by fitting the oil and water sorption curves to pseudofirst order and pseudo-second order models. References [1] C. Zarfl, D. Fleet, E. Fries, F. Galgani, G. Gerdts, G. Hanke, M. Matthies, Microplastics in oceans, Marine Pollution Bulletin 62 (2011) 1589-1591. [2] L.G.A. 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Kinetic parameters obtained by fitting the oil and water sorption curves to pseudo-first order and pseudo-second order models. OIL WATER q e (%) k 2 R2 q e (%) k 1 R2 F3 0.5% + PLA 686.7 3.4·10-4 0.9980 305.8 4.3·10-4 0.9837 F3 1% + PLA 627.1 1.7·10-4 0.9994 288.2 7.0·10-5 0.9207 F3 1.5% + PLA 639.5 3.8·10-4 0.9969 291.5 7.7·10-5 0.9597 F3 2% + PLA 583.8 1.1·10-3 0.9996 260.4 1.7·10-4 0.9735 NANO F3 0.5% + PLA 835.5 6.7·10-4 0.9997 355.9 7.3·10-5 0.9942 NANO F3 1% + PLA 804.8 3.7·10-3 0.9985 321.5 6.5·10-5 0.9916 NANO F3 1.5% + PLA 641.3 9.7·10-4 0.9937 294.1 9.4·10-5 0.9856 NANO F3 2% + PLA 594.8 8.2·10-4 0.9986 274.0 1.9·10-4 0.9843 NANO F2A 0.5% + PLA 942.6 7.4·10-4 0.9987 699.3 2.3·10-5 0.9733 NANO F2A 1% + PLA 788.7 4.1·10-4 0.9962 584.8 2.7·10-5 0.9746 NANO F2A 1.5% + PLA 730.6 5.4·10-3 0.9994 456.6 5.9·10-5 0.9863 NANO F2A 2% + PLA 745.8 1.7·10-3 0.9992 458.7 3.3·10-5 0.9575 NANO F2 0.5% + PLA 836.7 2.0·10-4 0.9987 531.9 4.1·10-5 0.9936 NANO F2 1% + PLA 771.7 3.7·10-4 0.9975 401.6 3.2·10-5 0.9673 NANO F2 1.5% + PLA 748.7 3.1·10-3 0.9991 369.0 5.7·10-5 0.9226 NANO F2 2%+ PLA 722.9 4.0·10-3 0.9996 371.7 3.9·10-5 0.9642 39 A 40 B 41 C