Cork Granules Research Articles

Evaluation of solid waste stratified mixtures as constructed wetland fillers under different operation modes

Based on the strategy that all processes can and should be modified to contribute to a circular economy, this work evaluates the recovery of waste solids as filler material in Constructed Wetlands (CWs) used for wastewater treatment. Five sets of lab-scale CWs were assembled with mixtures of five waste solids and operated to evaluate the removal of chemical oxygen demand (COD) and nutrients from urban and industrial-types of wastewater. The adaptation and growth of the macrophyte Phragmites australis in the mixed-filler CWs was also monitored. Although all evaluated waste solids showed to be acceptable substrates for macrophyte development and wastewater treatment, CWs assembled with mixtures of limestone waste and coal slag showed the best plant growth indicators and wastewater treatment efficiencies. The CWs assembled with mixtures of limestone waste and clay brick fragments or cork granulates showed to be suitable alternatives. With exception for CWs filled with mixtures of limestone and snail shells, pollutant removal efficiencies up to 95%, 86% and 83% were obtained respectively for COD, total phosphorous and total nitrogen, depending on the type of wastewater and mode of operation. Removal efficiencies were not significantly affected by increased hydraulic rate. The CWs can be operated to a hydraulic loading rate of 0.056 m/d, which corresponds to a retention time of 1.5 days. The valorisation of solid waste as a filler can contribute to CWs closely participating in the creation of circular flows for the reuse of waste solids.

Mechanical, thermal and acoustic behaviour of polymer-based composite materials produced with rice husk and expanded cork by-products

In this work, innovative polymer-based composite materials made with rice husk and expanded cork by-products have been produced and characterised. First, rice husks and expanded cork granules were studied separately to ascertain material properties, such as thermal conductivity, water vapour resistance, thermal stability and specific heat capacity. After that, different composite mixes were formulated and the resulting boards evaluated in terms of their mechanical, hygrothermal and acoustic properties. The influence of the different mix ratios and composite densities on the overall performance is also discussed. The experimental results indicate that higher contents of rice husk can contribute to improve the acoustic performance, while the incorporation of expanded cork granules in the composite formulations helps to reduce the thermal conductivity and improve the mechanical behaviour. The applicability of these composites in constructive systems such as walls and floors was assessed. For this purpose, the most suitable composite formulations were selected after a multi-criteria analysis was performed. The static and dynamic thermal performance provided by building solutions that included the selected composite materials was then evaluated. The results suggest that construction solutions based on these composite materials can be used in buildings, thereby contributing to reduce energy consumption during buildings’ service life.

Use of cork granules as an effective sustainable material to clean-up spills of crude oil and derivatives.

The use of cork granules for cleaning up crude oil or oil derivative spills and further oil recovery appears as a promising option due to their unique properties, which allow a high oil sorption capacity, low water pickup and excellent reuse. The present work reports the effect of oil viscosity on cork sorption capacity by using five types of oils (lubricating oil, 5.7 goil gcork-1; heavy oil, 4.2 goil gcork-1; light oil, 3.0 goil gcork-1; biodiesel, 2.6 goil gcork-1; and diesel, 2.0 goil gcork-1). The cork sorption capacity for light petroleum was also evaluated as a function of temperature and sorbent particle size. Additionally, improvements on oil recovery from cork sorbents by a mechanical compression process have been achieved as a result of a design of experiments (DOE) using the response surface methodology. Such statistical technique provided remarkable results in terms of cork sorbent reusability, as the oil sorption capacity was preserved after 30 cycles of sorption-squeezing steps. The sorbed oils could be removed from the sorbent surface, collected simply by squeezing the cork granules and further reused. The best operational region yielded near 80% oil recovery, using a cork mass of 8.85 g (particle size of 2.0-4.0 mm) loaded with 43.5 mL of lubricating oil, at 5.4 bar, utilising two compressions with a duration of 2 min each. Graphical abstract.

Loose cork granulates as possible new core element in noise barriers

This paper is a first study to evaluate the possible use of loose cork granulates as core element in noise barriers. To obtain the acoustical performance of loose cork granulates inside a noise screen, a small prototype of a noise absorbing barrier was designed and compared to commercial rock wool. The results obtained showed that these kinds of porous absorber, specially sorted and prepared, could be good sound absorbers with a certain broadband absorption spectrum.

Removal of antimony from water by iron-coated cork granulates

This study demonstrated the viability of the application of iron-coated cork granulates, previously developed for As removal, in the adsorption of Sb from water. Batch adsorption assays were carried out both for high Sb initial concentrations and typical environmental values. The ionic strength was varied in environmentally relevant scenarios by changing the concentration of NaCl as a background electrolyte.Adsorption kinetics were best described by the Elovich model at high Sb initial concentrations and the pseudo-second-order model at lower levels. Adsorption of Sb(III) was faster than Sb(V) and an increase in ionic strength decreased the rates of adsorption. Equilibrium data was modelled by the Freundlich and Langmuir isotherms and the maximum adsorption capacities were estimated as 5.8 ± 0.5 mg g−1 Sb(III) at pH 6 and 12 ± 2 mg g−1 Sb(V) at pH 3.Sb(III) adsorption was unaffected by pH and positively or neutrally affected by ionic strength, indicating that the adsorption mechanism was the formation of inner-sphere complexes. Sb(V) adsorption, however, was higher at acidic values and decreased with increasing pH, and was negatively affected by ionic strength. The surface charge of the adsorbent was also influenced by the presence of Sb(V), suggesting that Sb(V) is adsorbed by electrostatic interactions and outer-sphere complexation. Speciation studies were carried out with analysis of Sb(III) and no evidence was found of oxidation-reduction reactions occurring parallel to Sb uptake.Iron-coated cork granulates showed good potential to be used as adsorbents of both Sb(III) and Sb(V), with possible economical and environmental benefits.

'Green' composites prepared from polyfurfuryl alcohol and cork residues: Thermal and mechanical properties

Polyfurfuryl alcohol (PFA) is a biobased thermoset like matrix with high thermal performances and cork powder or cork granules are side stream product from cork stoppers’ production. They were processed together via compression molding. Structural investigations were made by means of FT-IR and thermo-mechanical measurements were performed using tensile tests, thermogravimetric analyses (TGA) and dynamic mechanical analyses (DMA). The fracture surface morphology controlled by scanning electronic microscopy (SEM) shows that cork cells are well filled by PFA and that homogeneous composites can be formed. The addition of PFA allows increasing sharply the elastic modulus and the tensile strength which attest for good adhesion between PFA and cork. The thermal degradation of cork/PFA composites is shifted to higher temperature (±20 °C) which indicates that PFA helps to prevent the cork decomposition. Finally PFA reduce significantly the absorption of water in composites.

Granulated cork with bark characterised as environment-friendly lightweight aggregate for cement based materials

The cork industry generates large quantities of waste, which has been studied for the application in the construction industry. However, the literature refers to it as cork waste (granulated or dust) in general, and its features have not been clearly specified. However, cork waste includes several by-products with different characteristics depending on the stage of process which they are generated in. The main goal of this study is to investigate the specific characteristics of one of those by-products that is granulated cork with bark, in order put to use as a lightweight aggregate in the construction industry. In this paper, its surface chemical properties are studied, by the first time, employing Fourier Transformed Infrared Spectroscopy and Energy Dispersive X-ray Spectroscopy and they are compared to those of cork. The chemical functional groups that are present at the granule surface, carbonyl and hydroxyl groups, are able to interact with cement components and water by important intermolecular chemical forces such as hydrogen bonds or dipole-dipole. The microstructure of grains is evaluated through image analysis, Scanning Electron Microscopy. The found cellular structure gives rise to density and absorption values similar to those of commercial lightweight aggregates and provides thermal insulating properties to this material. Then this material presents suitable properties to find a use as lightweight aggregate for concrete or mortar. The optimal replacement of aggregate by granulated cork with bark would contribute to a sustainable manufacture of cork providing an outlet for this waste.

Multi-scale foam : 3D structure/compressive behaviour relationship of agglomerated cork

This study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural polymeric foam - cork - mixed together with a small quantity of a bio-sourced resin.Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm3. Cork cell specific geometry is also confirmed. The volume of those cells lies around 10−5 mm3. Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.

Graphene-Enriched Agglomerated Cork Material and Its Behaviour under Quasi-Static and Dynamic Loading.

The use of cork for a variety of applications has been gaining significance due to environmental concerns and political agendas. Consequently, its range of applications is growing rapidly. In this work, aiming to improve its mechanical response for crashworthiness applications, cork agglomerates were enriched by small quantities of graphene oxide or graphene nanoplates in order to observe a resulting improvement of the mechanical behaviour during quasi-static and dynamic compressive loading cases. To produce homogenous cork agglomerates including graphene, the material was previously dispersed into granulated cork using stirrers to achieve a good distribution. Then, the typical procedure of compression and curing was carried out. Magnified images attest a good dispersion of graphene into the cork matrix. Mechanical testing was performed for a variety of graphene concentrations (0.1, 0.5 and 1.0 weight %), becoming clear that the beneficial effect of including graphene (either oxide or nanoplates) is related to a later densification stage while keeping the same stress plateau levels.

Design of alkali-activated materials for a modular green wall and green roof system

This study presents the work developed with alkali activated mixtures to be used as component of a new modular green wall and green roof system (GEOGREEN). The aim is to find the most appropriate composition of alkali-activated mixture to maximize water absorption and porosity and also find a good mechanical strength with reduced density. Alkali-activated mixtures were produced using two precursors, mine waste mud from Panasqueira mine (W) and ground waste glass (G) and two alkaline activators, sodium silicate (SS) and sodium hydroxide (SH). A ventilated oven was used to speed up the curing process. Variables as percentage substitution of W per G, molar concentration of SH, cure length and temperature, were tested to identify the reference mixture. After these tests different percentages of aggregates as sand (S), expanded cork granules (C) and expanded clay (A) were added to reference mixture (REF). Results indicate that S25 obtained the maximum compressive strength of 35 MPa after 7 curing days. However, about 30% compressive strength loss is observed after immersion of this mixture in water for 24h. Capillary absorption coefficient can reach to 4,77 kg/m2.h0,5 with C25 and to 4,11 kg/m2.h0,5 with S25. Also C50 enables a 20% density reduction compared to REF.

Expansion volume of alkali activated foamed cork composites from tungsten mining mud waste with aluminium

Several mixes of alkali activated foams from tungsten mud waste (MW), grounded glass (GG) and metakaolin (MK) were developed incorporating expanded granulated cork (EGC). This study presents preliminary results of the expansion process obtained with the addition of aluminium (AL) powder as a foaming agent. 0.3 wt.%, 0.4 wt.% to 0.5wt.% of AL powder were added to the alkali activated matrix. The physical and mechanical properties of the obtained foams, the effects of the type and amount of the foaming agent added are presented and discussed. Highly porous structures were obtained, with overall expansion up to 68.2% when the AL powder was added. The size and distribution of pores are shown. The compressive strength of foams in the case of highly porous structures achieved of 1.2 MPa for the samples containing 0.5 wt.% of AL powder. Mechanical and thermal properties of the cured structure are good and can therefore be used for applications in acoustic panels and lightweight prefabricated components for thermal insulation purposes.

Effect of elevated temperatures on alkali-activated tungsten mining waste based materials

Generally, alkali-activated materials (aka geopolymers) present good behaviour at high temperatures, but previous studies of geopolymers under elevated temperatures are, in most cases, focused on metakaolin or fly ash based geopolymers, making the information on geopolymers with mining waste mud almost inexistent. In this paper, were analysed geopolymers with different combinations of mining waste mud, waste glass powder, metakaolin and expanded cork in a total of 15 different mixtures using sodium hydroxide and sodium silicate as alkaline activators. Materials particle size used is under 500 μm for mining waste mud, waste glass powder. Some mixtures also included expanded granulated cork with particle size between 2 to 4 mm. Ten samples with 40 × 40 × 40 mm dimensions were used for the compression test, one sample for the TGA test, and one cube (100 × 100 × 60 mm) with a frustoconical hole (50 mm deep) and a 100 × 100 × 25 mm cover, for the cup test. All the mixtures were cured for 24h at a temperature of 60 °C before being demoulded, and left at room temperature until they reach 7 days to be tested. On the 7th day, of each mixture, samples were placed in a static furnace before the compression test submitted to a temperature of 800 °C during 2h. Then, the compression test was performed and the values before and after exposure to high temperatures were compared. Were recorded maximum gains of 724% and maximum losses of 100% in the compressive strength. This preliminary result shows the potentials of mining waste alkali-activated materials for elevated temperatures applications.

Physical and mechanical performance of cement-based renders with different contents of fly ash, expanded cork granules and expanded clay

In recent decades, there has been a demand for new cladding solutions with higher thermal efficiency. Mortars with an improved thermal performance are one such solution. The biggest challenge in developing these mortars consists in achieving a lower thermal conductivity, while still maintaining an appropriate mechanical and water resistance performance with a low environmental impact.The aim of this study is to analyse the physical and mechanical performance of 20 cement-based coating mortars (renders) with different contents of a SCM – supplementary cementitious material (fly ash) used to replace cement, and of two insulating aggregates (expanded cork granules, expanded clay or a mix of both) replacing sand.The reduction of cement binder and sand aggregate contents led to lower thermal conductivity and a decrease of the mechanical properties. However, the balance between the physical and mechanical performance allows different applications, reaching thermal mortars with distinct EN 998 classes: (i) thermal conductivity T1 or T2; (ii) compressive strength CSI or CSII; (iii) water capillary absorption W0 or W1.

Cork–PLA composite filaments for fused deposition modelling

We report design and development of cork–poly(lactic acid) (PLA) biodegradable filaments for fused deposition modelling (FDM), which is an additive manufacturing technique. Composites of varying cork composition were melt compounded in an internal mixer and compression moulded for characterisation of mechanical, thermal and morphological properties. Inclusion of cork granules decreased the tensile strength, but improved impact strength. As the cork percentage increased, density of the composites decreased. Hence, the specific modulus and specific tensile strength properties improved as the cork content increased in the composites. Tributyl citrate (TBC), a biodegradable plasticiser, was used to overcome the inherent brittleness of PLA. TBC decreased the modulus, tensile yield strength; however it increased ductility of the composites. A selected cork composite was used for filament production and it proved to be suitable for fused deposition modelling. 3D printed composites were compared with compression moulded composites. 3D printing resulted in slightly lower elastic modulus and tensile yield strength, but higher elongation at break compared with compression moulded composites.

Cork as a sustainable carbon source for nature-based solutions treating hydroponic wastewaters – Preliminary batch studies

Reusing by-products is an important strategy to ensure the preservation of natural capital and climate change mitigation. This study aimed at evaluating the potential of cork granulates, a by-product of winery industry, as an organic carbon (OC) source for the treatment of hydroponic wastewaters. First, chemical characterization was performed and discussed. Secondly, batch studies were performed using synthetic hydroponic wastewater to understand the role of particle size (PS), pH and contact time (CT) on the release of OC. The suberin is the major compound, representing >50%. It was noticed that a variance on the content of suberin across species, within the same species and depending on the extraction part (belly, cork and back) could be expected. >60% of the sample is composed by carbon while <1% was nitrogen (high C:N ratio), indicating a low risk of releasing organic nitrogen. The statistical results suggested that the main effect of PS on the release of OC is greater than both, CT and pH. The chemical release of OC gets slower with time, being this effect greater as the PS increase. Moreover, estimations showed that using the 4 mm PS, the amount of water treated would be twice the amount if the 8 mm PS had been used. The PS seems to play an important role at design nature-based solutions (NBS) focused on denitrification. The surface response methodology indicates a significant negative interaction between CT and PS suggesting that the mathematical model could be used for further optimization studies. The reuse of organic by-products as filter media seems to be an economic and environmentally friendly alternative to enhance denitrification in NBS, while preserving natural capital. However, further real scale and long-term experiments are needed to validate cork's potential as an “internal” OC source for NBS.

Screening of Solid Waste as Filler Material for Constructed Wetlands

The reuse of solid waste can contribute to reducing Earth’s resource depletion, directly through use in the original production processes or by valorisation in alternative applications. In the present work, ten solid wastes were evaluated as candidates for filling material in constructed wetlands (CWs). For that purpose, physical characterization, leaching and adsorption tests were conducted. Limestone fragments and brick fragments resulting from construction activities, coal slags resulting from power plants, snail shells resulting from the food and catering industry, and cork granulates resulting from the cork industry have potential for use as CW fillers. These five materials have adequate physical properties and some capacity to adsorb phosphorous and organic compounds from wastewater. On the other hand, crushed eggshells resulting from egg farms, dealcoholized grape pomaces resulting from alcohol distilleries, olive seeds waste from olive-oil mills, and pine bark fragments and wood pellets resulting from forestry cleaning activities, wood mills and pulp mills did not demonstrate sufficient potential to be used as CW fillers, either because they have very low adsorption capacities or leach compounds in contact with water, or because they have less adequate physical properties. None of the tested solid wastes showed the ability to adsorb nitrogen compounds. Although the five selected materials do not present a special capability for adsorption of nitrogen, phosphorous and organic compounds, they can all be valued as CW fillers, representing a way to reduce the amount of solid waste sent to landfills.

Granulated cork as biosorbent for the removal of phenol derivatives and emerging contaminants

This study evaluated the ability of cork to adsorb a broad range of phenolic, pharmaceutical and cosmetic compounds: phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol, pentachlorophenol carbamazepine, naproxen, ketoprofen, diclofenac, triclosan, and methyl paraben. The effect of variables such as the compound concentrations and the amount of cork were studied resulting in a highly pH dependence in the case of phenolic compounds. Maximum removal percentages and uptake values of 75% (1.61 mg/g) for 2,4-dichlorophenol, 55% (1.25 mg/g) for 2-nitrophenol, 45% (1.47 mg/g) for 2-chlorophenol, 20% (0.63 mg/g) for phenol, and 100% for pentachlorophenol, were obtained for a 30 mg L−1 solution at pH 6, showing that the adsorption process increased with greater electronegativity of the phenolic substituting group. Removal percentages and uptakes of 82% (3.56 mg/g) for naproxen, 57% (2.31 mg/g) for ketoprofen, 50% (1.84 mg/g) for carbamazepine, 50% (1.78 mg/g) for methyl paraben, 100% for sodium diclofenac, and 100% for triclosan, were obtained using 5 mg of cork and a 1 mg L−1 solution of each compound. The adsorption process was almost complete after 30 min for all the micropollutants. Experimental equilibrium data were analysed by Freundlich and Langmuir adsorption models. Cork has proved to be an effective sorbent for the removal of phenols and emerging contaminants from contaminated waters and is a readily available material that can be acquired at minimal or no cost in cork-producing areas.

Arsenate and arsenite adsorption onto iron-coated cork granulates

There is a growing demand for low-cost, effective adsorbents for arsenic removal from water intended for human consumption in affected rural areas. This work presents a novel adsorbent based on the coating of cork granulates with iron (oxy)hydroxides for the removal of As(III) and As(V) from aqueous matrices.A 26–3 fractional factorial design was used to determine the optimal conditions for the iron coating procedure. The optimal adsorbent was produced by coating low-density cork granulates with iron (oxy)hydroxides precipitated from a 0.05 mol L−1 FeCl3 solution at pH 7, 20 °C temperature and 20 g L−1 S/L ratio, in a single coating cycle.Arsenic adsorption was found to be dependent on pH, with inverse trends for As(III) and As(V). The iron leaching from the adsorbent was also taken into account to select the optimum pH, which was pH 9 for As(III) and pH 3 for As(V).Adsorption kinetics were better described by the pseudo-second-order model for As(III) and the Elovich model for As(V). Equilibrium was reached in 16 h for As(III) at pH 9 and 48 h for As(V) at pH 3. The isotherm models indicated different adsorption behaviours for As(III) and As(V), with better fits by Langmuir and Freundlich models, respectively. The Langmuir maximum adsorption capacity of iron-coated cork adsorbent for As(III) at pH 9 was 4.9 ± 0.3 mg g−1. However, at low equilibrium concentrations, As(V) adsorption was higher than As(III) (e.g. 2.1 ± 0.2 mg g−1 in equilibrium with 0.16 ± 0.03 mg L−1).Speciation studies and XPS analyses indicated that no substantial oxidation of As(III) to As(V) occurred during the adsorption process.The study shows that iron coating can enhance both arsenate and arsenite adsorption capacity of cork materials, leading to an innovative natural adsorbent with high resilience and stability, with possible application in arsenic remediation.

Application of rice husk in the development of new composite boards

The main objective of the paper is to propose a new composite material incorporating rice husk. This paper reports an experimental study on the mechanical, thermal and acoustic performance of new composite boards made of rice husk waste intended for construction applications. In this study, rice husk was mixed with expanded cork granules or recycled rubber granules in 50/50 and 75/25 (weight percent) proportions. A TDI-based polyurethane pre-polymer was used as binder in 20% of the mass of the fillers. A sufficient number of small boards were produced to perform small-scale tests and assess properties such as compressive strength, thermal conductivity, dynamic stiffness, improvement in impact sound insulation, sound absorption and transmission loss.The results are very interesting, in particular: the thermal conductivity, at 10 °C, varies from λ10 = 60.0 mW/(m.K) to λ10 = 74.3 mW/(m.K); the weighted reduction of the impact sound pressure level, ΔLw, ranges from 20 dB to 27 dB; the noise reduction coefficient (NRC) ranges from 0.15 to 0.45, with maximum sound absorption coefficient of 0.96 for composite B1. These results suggest that optimized construction solutions based on these composite materials could improve the thermal and acoustic performance of buildings.

The parameters that affect the supercritical extraction OF 2,4,6-trichloroanisol from cork

The contamination of wine by 2,4,6-trichloroanisol (TCA) derived from the cork stopper is a huge problem for the wine industry. This work shows the results of TCA extraction using supercritical CO2. Cork granules (6% moisture) were placed forming a fixed bed within a high-pressure vessel. The CO2 was made to continuously flow over this. The TCA removal was compared at different operating conditions (pressure, temperature, flow rate or extraction time). TCA removal was not possible in dried cork. Density had a positive impact in TCA removal due to the solvent capacity increase. An increase in the supercritical fluid temperature over 60 °C impaired the TCA extraction. High residence times benefited the extraction. At high CO2 density of 585 kg m−3, TCA elimination below the detection level was achieved in 8 min residence time. This required relatively low solvent to cork mass ratios (43 kg CO2 kg−1).