Development of Cork-Bamboo-Latex as An Alternative Composite for Bottles Stoppers

. It was possible to observe that the cork-bamboo-latex composite produced exhibited a good adhesion of all components and similar characteristics. However, it presented a slight increase in the density (from 0.37 g/cm 3 to 0.65 g/cm 3 ) and Young's modulus (from 0.033 MPa to 0.037 MPa) producing a stiﬀer material mainly due to bamboo presence. �e migration of the stopper components (cork, bamboo, or latex) for the wine was not detected, as well as there was no visible interaction between wine and composite. In this work, the cork-bamboo-latex stopper fabricated presents a potential application as an alternative material to wine stoppers and stimulates the production of a sustainable material.


INTRODUCTION
Cork stoppers are produced from the outer part of cork oak, Quercus suber L [1]. e cork oak bark removal must be done a er the tree reaches 25 years.Its periodic extraction takes place every nine years, depending on the radial growth and the region [2].
Cork is an outstanding material widely used as a sealing bo le in the wine industry because it is a natural, renewable, and sustainable raw material [3].Furthermore, its physic-chemical and mechanical properties, such as low permeability to liquid sand gases, low density, high compressibility and exibility, and chemical and microbiological stability provide suitable characteristics that arouse the interest of the manufacture of cork stoppers [4].
In the current market, cork is used to manufacture stoppers.Nonetheless, during cork processing, considerable amounts of residues are produced.Due to the low granulometry of the residues, the by-products obtained (about 20%) are not suitable for conventional cork applications and, for this reason, they are applied in other areas, such as cork pavement, insulation panels, composites, and as cork ller in agglomerated wine stoppers [7].Nevertheless, it can be considered a sustainable material since its origin is a vegetable one, and its degradation does not generate microplastics [8].
Slow growth and development of the cork bark and the globalization wine trade encouraged the production of new types of stoppers [9].Cork-based materials have been developed, as well as composite materials which combine cork and their by-products with adhesive and natural bers [10].ese composites could be employed as wine stoppers, which could be considered eco-friendly materials [11].
Cork agglomerated stoppers are obtained from the corking process as granulated cork.As a natural ber, bamboo stands out and it is used as reinforcement or ller in composite materials [12].Bamboo bers have a similar composition to a cork since it contains lignin, cellulose, hemicellulose, and extractives.
ey have been used in textile, paper, construction, package, and healthcare areas, due to advantages such as low density, low cost, high mechanical strength, stiffness, and anti-bacterial, anti-UV, and antistatic properties [13].
Regarding composites reinforced with bamboo bers, it can be highlighted that polylactic acid (PLA) samples reinforced with kenaf and bamboo bers presented high tensile strength and stiffness compared to singleber composites [14].Agglomerated polyurethane-bamboo bers samples presented ductile behavior under compressive forces, and they presented low swelling/water absorption capacity; they are suitable for non-structural applications [15].
High-density polyethylene-sisal-cork samples were produced by extrusion, and it was observed that the best mechanical performance was obtained using 2% of maleic anhydride as a coupling agent.In addition, high-density polyethylene-coconut-cork extruded samples also presented improved mechanical properties with the addition of the coupling agent, but also, the presence of 10% of coconut bers function as reinforcement in the composites [16].Agglomerated materials based on cork, bamboo bers, and an adhesive, such as latex, could be potential composite stoppers, besides being environmentally friendly.us, this work aims to develop a cork-bamboo-latex composite and to evaluate the interaction between three composite interfaces as well as their mechanical properties to produce an alternative material to wine stoppers.

Materials
e commercial agglomerated cork ( ) with an average particle size (of 1-2) mm was supplied by Logicork (Portugal).Raw bamboo (Bambusa vulgaris, FB) was obtained from the Forest Institute of the Rural Federal University of Rio de Janeiro (Seropédica, Brazil).It was peeled, pressed, and crushed.Pre-vulcanized NR Latex (LT), used as adhesive, was donated by the State University of Rio de Janeiro (Brazil).e wine (VV) employed at the immersion test was based on an Uruguayan wine produced from Tannat grapes (Concha Toro®, 2015).In addition, solid (RM) and agglomerated ( ) used wine stoppers, collected as discarded material from local commerce, were also employed and characterized to compare them to the agglomerated virgin commercial stoppers (RV), obtained in the local commerce, and to compare to the produced composite stoppers in this work.
Composite manufacturing e raw materials were dried at 70 ºC overnight before further treatments.
ey were mixed according to the respective amounts: 35% of cork, 35% of bamboo, and 30% of latex.
e composite was mechanically pre-mixed (Fisatom) for 15 min and compression-molded manually in glass molds to produce cylindrical samples (19x24 mm).e stoppers produced (CMP) were then dried and crosslinked in the oven (equipment FANEM) at 110 ºC for 48h.e glass molds were manually discarded, and the samples were conditioned at room temperature in a desiccator.
Immersion Test e commercial agglomerated cork ( ) and the cork-bamboo-latex composite produced (CMP) sizes were previously measured (average diameter and height dimensions) to determine their densities.ree samples of each type ( 1-3 and CMP 4-6, respectively) were partially immersed in 10 mL of wine (corresponding to 5 mm of height), placed in a closed glass ask, and kept in the refrigerator for seven days.A er the removal of the wine medium, the samples were weighed, and their dimensions were measured.e immersion test aims to observe the permeation of cork and bamboo residues to wine and the fungi's proliferation.
Composite Characterization e cork-bamboo-latex stoppers were analyzed by Fourier transform infrared spectroscopy (FTIR) using an ATR accessory.e spectra were collected on Spectrum 100 (PerkinElmer) in a range of 4000-600 cm -1 at 32 scans with a resolution of 4 cm -1 .
e compression tests on the commercial agglomerated cork and the produced composite stopper materials were performed until 60% strain in a universal testing machine UMC 300 (Contenco).e samples (19x24 mm) were radially compressed at a constant rate of 2 MPa/min using a 20 t load cell.e compression tests were performed in triplicate and the stress-strain average curve was recorded to obtain Young's modulus.
Microbial analysis of the composite e cork-bamboo-latex composite produced was crushed and diluted (1:10) in an aqueous 0.1 % wt.peptone solution (peptone 1 g/L and sodium chloride 8.5 g/L solution).An aliquot (1 mL) of this solution was inoculated onto the potato dextrose agar plates and incubated at 30 °C for 72 h for molds and yeasts growth.A er the incubation period, colony counting was expressed as the number of viable colonies per weight of cork material in grams (CFU/g).
All analysis that was performed in triplicates were evaluated by ANOVA-1way analysis, (factor: composition; levels: CMP e ), level of signi cance of 95%.Tukey test revealed the signi cant difference between pairs, level of signi cance of 95%.

RESULTS AND DISCUSSION
e cork-bamboo-latex composite produced has a cylindrical shape, dimensions values typically for wine bo les, and brown coloration [17].e weight, diameter, height, and density changes to stoppers before and a er the immersion test are displayed in Table 1.
e cork-bamboo-latex composite produced is heavier and denser than commercial agglomerated cork stoppers.Probably, this higher density is due to the bamboo used in the preparation of the composites stoppers which presents an average density of (0.6-0.7) g/cm 3 [18].Different parts of the cork can also in uence (increasing or decreasing, depending on the case) the density of the cork stoppers [19].Corks from different manufacturers can present distinct densities.e incorporation of bamboo parts to cork granules physically adhered contributes to increased mechanical properties, though the light weight of bamboo could diminish the composite density.However, the added components (bamboo, latex) to cork increased the samples density [20].However, the highest difference in the density value is found a er the immersion test, which leads to the conclusion that the bamboo component is the factor that most contributes to the increase in the density of the cork stopper.
e results a er the immersion test in wine showed that both materials ( and CMP) presented weight gain.However, only the cork-bamboo-latex composite presented an increase in diameter, while commercial cork stoppers (an average density of 0.371 g/cm 3 [21]) retained their size a er seven days of immersion in wine.
is observation is re ected in the density data, which were raised mainly for cork-bamboo-latex samples.
e composite stoppers produced (an average density of 0.653 g/cm 3 ) exhibited a relative increase of 31.02% in density and a slight increment in their diameter, whereas the commercial cork stoppers presented an increase of 6.26% in density.Usually, commercial cork stoppers also present wine absorption, which usually stabilizes a er months of contact with the liquid (3-24 months) and it would be the result of micro capillarity or evaporation-condensation phenomena [22].
Tukey test was used to verify if there is a difference statistically signi cant between both corks employed in this study adopting 95% of con dence. is test indicated that there is a signi cant difference between the wine absorption (swelling in the media (wine)) from stoppers and the CMP samples (p<0.05)[5]. is measurement suggests that there was a greater migration of wine to the cork-bamboolatex composite produced in comparison with the commercial agglomerated cork. is may be related to the automatic compression-molded process of the commercial agglomerated stoppers, where there is improved cork packaging.On the other hand, the composites produced were compressed-molded manually which makes it difficult to control the particle packaging.Besides that, there are the intrinsic properties of cork and bamboo, where cork can be considered a hydrophobic material, where the presence of a hydrophilic material, such as bamboo residue, aggregated to it, could increase the absorption of uids rich in -OH groups, such as wine [23].Cork absorbs wine is related to the uid diffusion trough the cork's cell wall, where the driving force is the concentration gradient [21].
FTIR spectra for the solid (RM) and agglomerated ( ) cork stoppers collected from local commerce (cork stoppers used) compared with cork-bamboo-latex composite (CMP) produced and agglomerated virgin (RV) cork stopper is shown in Fig. 1. is comparison aims to show that the commercially available corks have a similar pro le, they present the same main FTIR bands of the cork-bamboo-latex composite produced, indicating that the cork phase is dominant.Fig. 1 shows bands at 3340 cm -1 characteristics of OH bonding of the cork.which contain OH bonds in their structure [4].Bands from 2960 to 2850 cm -1 can be a ributed to the CH 2 vibration of the carbon chain present in cork components [24].
However, only the cork-bamboo-latex composite stoppers showed a band at 2960 cm -1 and a slight displacement of the C-H bands to 2922 and 2853 cm -1 . is evident band may be related to the C-H stretching vibration (CH 3 ) of latex which is the only different component compared to the other samples.e shi can be associated with the composition since it presents cork, bamboo, and latex.Furthermore, it could be due to water absorption related to the manual manufacturing process, which contributed to bands broadening.Bands at 1736 cm -1 are related to the carbonyl group from suberin.Some bands (1617, 1511, and 1448 cm -1 ) were a ributed to C=C aromatic ring stretches.e band at 1376 cm -1 is ascribed to O-H in-plane deformation in polyphenols mainly from lignin [25].e 1150 cm -1 absorption band is associated with the stretching vibrations of C-O-C bonds characteristic of the polysaccharides with 1 → 4 glycosidic linkage (cellulose and hemicellulose compounds) [26].Other bands (~1124 and ~1053 cm -1 ) are also a ributed to the C-O-C bond, which could be present in the FTIR spectra of samples, however, due to the broadening band, these bands could be overlapped.e region from 840 to 720 cm -1 can be associated with ring vibrations (C-H out of the plane and in-plane bending) of the lignin [24].e highest difference found in the composite-produced spectrum was the evident band at 2960 cm -1 and the low intensity of the C=O band at 1737 cm -1 .
To analyze the release of cork, bamboo, and latex residues from the composite produced to the wine a er the immersion test, an FTIR analysis of each component (Fig. 2a) and wine before and a er the immersion test (Fig. 2b) was performed.Fig. 2a shows that the components of the composite produced present the same bands previously cited.A strong absorption band at 3357 cm -1 is ascribed to hydrogen-bonded O-H or N-H.It is worth noting that the latex spectrum exhibits a band in 2960 cm -1 , the same one found in the cork-bamboo-latex composite.
is band is characteristic of the asymmetric stretching  [27].e band at 1640 cm -1 is assigned to the C=O symmetric stretching of amide I also present in the latex.1450-1370 cm -1 region is related to the angular deformation of CH 2 and CH 3 groups, as well as the C-OH and N-CH 2 -N stretching vibration.is last group (N-CH 2 -N) could be con rmed by the 1160 cm -1 band [28].FTIR spectra of the wine a er the immersion test are displayed in Fig. 2b.

Applied Materials and Technology
e intense band at 3306 cm -1 is assigned to O-H groups from water and ethanol.Region 1800-900 cm -1 is considered a ngerprint region and provides valuable information about wine characteristics [29].[30].FTIR analysis showed similar bands pro le for all samples even a er the immersion test.ere was no modi cation of the spectra, either by the presence or absence of a band or by band displacement.Apparently, there was no components release of the corkbamboo-latex composite produced to the media (wine).
e mechanical performance of the cork stoppers was studied by compressive experiments, Fig. 3 (1 curve of each triplicate is shown).
e compressive behavior response of cork stoppers can be divided into three regions: the rst region (up to 7.5% strain), which is an elastic area corresponding to the reversible bending of the material; the second region (up to 35% strain), where there is large plateau corresponding to elongation of the material; and, the last one, where there is a compaction region characterized by an abrupt increase in strain when critical stress is reached [31].
e cork-bamboo-latex composite stoppers display anincrease in Young's modulus (from 0.033 MPa ( ) to 0.037 MPa (CMP)) when compared with commercial agglomerated cork (p<0.05).Higher elastic modulus indicates that the produced composite stoppers support a higher load to reach 60% of deformation leading to an increase in the stiffness.is increase in Young's modulus could be also related to the higher density of the corkbamboo-latex composite in comparison with the commercial agglomerate cork stopper.Cork might be physically anchored in the matrix, but it does not contribute considerably to the mechanical properties [32].e increase in the maximum strength for CMP (from 4.11 g/cm 3 ( ) to 4.72 g/cm 3 (CMP)) could indicate that the matrix is well compacted and there was a good adhesion between the components of the composite produced [16].However, the statistical analysis of data did not show signi cant difference between and CMP cork stoppers for maximum strength (p>0.05).
e composite mechanical properties could interfere with the wine bo le seal negatively, making it difficult to place the stopper on the bo leneck, it could also contribute positively, preventing the permeation of the liquid out of the bo le.Microbial analysis of molds and yeasts in the composite presented 1.5 x 10 2 CFU/g (colony-forming unit per gram) indicating the microorganism's presence, which is undesirable even in low concentrations.A possible reason for the development of molds can be related to humidity present in the composite due to poor efficiency in the drying process, regarding its time and temperature [16,33].In addition, the bamboo hydrophilicity could contribute to microorganisms' proliferation [34].One of the treatments previously adopted to prevent the proliferation of fungi was chlorination.However, if the washing and sterilization process was not well performed, there was the formation of undesirable chlorophenol compounds.
ese compounds permeate the cork, causing avor unpleasant and compromising the wine quality.For this reason, nowadays, this treatment is completely forbidden in cork-stopper manufacturing processes [35].Unfortunately, the musty and moldy avor in wine is associated with the cork stoppers, which would be associated with cork's 2,4,6-trichloroanisole.Anisoles are related to at least 80% of cork taint [36].A possible route to change microorganism growth could be related to surface treatment by plasma radiation [22].Brazilian legislation do not include microbiological parameters for cork stoppers themselves, but the microbiological parameters should reach the ones for the foods in contact with the packaging, RDC n. 12/01 [37].Fig. 3. Compressive properties of the commercial agglomerated cork ( ) and cork-bamboo-latex composite stopper (CMP) until 60% deformation.

CONCLUSIONS
It was possible to produce a cork-bamboo-latex composite stopper that exhibits properties similar to commercial agglomerate corks.It was observed that there was no migration of the components used in the composite's fabrication (cork, bamboo, or latex) for the wine, as well as there was no visible interaction between wine and composite observed by FTIR.It was also observed that the composite produced was physically agglomerated and exhibited a good adhesion of all components.roughout the immersion test, it was possible to verify the presence of molds and yeasts in the composite, even in low amounts.
e composite produced presented mechanical properties suitable for the application of wine stoppers.However stiffer than commercial stoppers, this feature can be positive in the sealing process.It is considered that the cork-bamboo-latex composite presents a potential as an alternative material to wine stoppers since the substitution of part of the cork with bamboo could reduce its use and the cost of the material, as well as stimulates the production of a sustainable material.It is worth mentioning that further development is required to avoid mold and yeast growth.

Fig. 1 .
Fig. 1.FTIR spectra of the commercial solid (RM), agglomerated ( ), agglomerated virgin (RV) cork, and cork-bamboo-latex composite (CMP) stoppers.is region includes stretching vibration of C-O, C-N, C-H, C-C, N-H e C=O bonds which are typical of different molecules present in wine[30].FTIR analysis showed similar bands pro le for all samples even a er the immersion test.ere was no modi cation of the spectra, either by the presence or absence of a band or by band displacement.Apparently, there was no components release of the corkbamboo-latex composite produced to the media (wine).emechanical performance of the cork stoppers was studied by compressive experiments, Fig.3(1 curve of each triplicate is shown).ecompressive behavior response of cork stoppers can be divided into three regions: the rst region (up to 7.5% strain), which is an elastic area corresponding to the reversible bending of the material; the second region (up to 35% strain), where there is large plateau corresponding to elongation of the material; and, the last one, where there is a compaction region characterized by an abrupt increase in strain when critical stress is reached[31].ecork-bamboo-latex composite stoppers display anincrease in Young's modulus (from 0.033 MPa ( ) to 0.037 MPa (CMP)) when compared with commercial agglomerated cork (p<0.05).Higher elastic modulus indicates that the produced composite stoppers support a higher load to reach 60% of deformation leading to an increase in the stiffness.is increase in Young's modulus could be also related to the higher density of the corkbamboo-latex composite in comparison with the commercial agglomerate cork stopper.Cork might be physically

Table 1 .
Physical properties of the commercial agglomerated cork stoppers ( ) and produced composite (CMP) stoppers vibration of the C-H bond included in the CH 3 group of latex in the composite