Today's challenge is to produce a biodegradable materials for packing which can partially replace traditional plastic materials. Starch-based biodegradable plastics are less harmful to the environment and breakdown faster than regular plastics. The goal of this research was to produce and characterize a biodegradable film(BF) made from Sorghum bicolor (L.) starch and glycerol plasticizer. The produced film contained two amounts of Sorghum bicolor (L.) starch (5 g and 10 g) and three percentages of glycerol (25%, 30%, and 40%). The Sorghum bicolor (L.) and biodegradable glycerol-based plastic film had the lowest density, water absorption, and thickness swelling of 0.99 g cm, 55.72%, and 10.72%, respectively. The tensile strength is maximum at 9.97 MPa and and elongation obtained is 23.84%. The Sorghum bicolor (L.) starch and glycerol-based biodegradable film decomposed by 69.23% after biodegradability testing of one week.Biodegradability; Biodegradable Film; Glycerol; Sorghum Bicolor (L.) Starch; Tensile Strength
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Introduction
Bioplastics are made from biomass components such as lipids, polysaccharides and proteins. 1-3. These synthetic materials derived from renewable organic resources have been demonstrated to be efficient alternatives for petroleum-based plastics, and they are expected to reduce our dependence on fossil fuels and the amount of plastic trash generated 4. Bioplastics have the potential to alleviate the problem of the world’s ever-growing plastic waste because they are biodegradable and have applications in a range of industries, including packaging, opt-electronics, agriculture, and pharmaceuticals 5. Overall, sustainable bio-plastics offer an excellent alternative to petroleum-based plastics 6.
Polysaccharides are one of the materials utilized to manufacture plastic film that are biodegradable and are useful in a range of industries, including the pharmaceutical and food industries 7. Environmentally friendly polysaccharide-based bio-plastics have outstanding mechanical characteristics, resistivity, and the capacity to block the escape of O2 and CO2 gases at low or moderate humidity 8. Glycerol is a byproduct of the oil or bio-diesel industries, whereas starch (polysaccharide) with thermoplastic properties is widely produced domestically. Amylose and amylopectin, two of starch’s most essential components, are biopolymers.
These biopolymers are useful as barriers in raw material packaging materials. Starch is used in industrial foods and to manufacture biodegradable films that can partially or entirely replace plastic polymers since it is affordable, renewable, and has high mechanical properties 9. Because of starch abundance, renewability, cost-effectiveness, and biodegradability, its recognized as one of the best natural polymers. 10, 11. Nevertheless, the poor mechanical strength and ability to dissolve in water of starch biopolymers have shown to be significant limitations.
Glycerol, as viscous liquid is known as glycerin. It is the most basic trihydric alcohol with colourless, odourless, and sweet taste. It is slightly dissolved by solvent such as ether, ethyl acetate, and dioxane. It is completely soluble in both water and alcohol. Plasticizers increase brittle film flexibility while simultaneously weakening and increasing moisture permeability 12. Glycerol has a significant impact on the mechanical properties of the bio-plastic films (P < 0.05). Because of the lower glycerol concentration, the tensile strength of the film and barrier qualities will be superior to films with higher concentration 13. Biodegradable polymers based on starch are more environmentally friendly and decompose faster than ordinary plastics 14.
Biodegradable polymers based on agricultural resources have evolved in recent years 15. Starch, a naturally occurring carbohydrate polymer, has gotten the most attention for its potential as a raw material for bioplastic manufacturing 16. Plasticizers are widely utilized in the fabrication of starch-based polymers due to their brittleness. It ensures that the resulting plastic is not easily breakable and brittle, but rather robust and flexible 17. Glycerol and Sorbitol are two common plasticizers used in the production of bioplastics 18, 19. Many researchers used fillers as reinforcement to improve the mechanical and physical properties of starch-based biodegradable polymers. When a filler is added to a biodegradable plastic, its tensile strength and Young’s modulus improve 20, 21.
The present challenge is to produce packaging material that are biodegradable to replace standard plastic. Biodegradable polymers based on starch are more environmentally friendly and decomposes faster than ordinary plastics. In separate investigations, Basilla 22 and Cheong et al. 23 developed biodegradable films from cassava starch, foamed disposable food containers made from nanoclay and starch, and bio-based polymers made from sago starch.
Current study focused on producing biodegradable bioplastics from natural sources, Sorghum bicolor (L.) starch, and increasing mechanical and physical qualities by employing glycerol as plasticizers, followed by characterization.
Materials and methods
Sorghum bicolor (L.) starch and glycerol (92.09% Ajax Finechem Univar ® Analytical Reagent) were used as plasticizers and film-forming agents to create a biodegradable film.
Film preparation
Sorghum bicolor (L.) starch (5 and 10 g) and glycerol (25%, 30%, and 40%) were combined. After that, 100 mL of distilled water was added to the resulting mixture. The entire solution was heated at 80°C for 15 minutes while being stirred. The heated mixture was placed on glass and petri plates and left in a 17°C temperature drop chamber for three to four days.
Characterization of the biodegradable film
The biodegradable film’s density, water absorption, thickness/swelling, tensile strength, and biodegradability were all evaluated.
Density
The biodegradable film’s density was calculated using the ISO 1183 (ASTM D792) test method.
Moisture content
To determine the moisture content, a modified approach from Sanyang et al.,24 was employed. The bioplastic samples were cut into 1.5 X 1.5 cm2 pieces, the initial weight (Wi) of the sample was estimated, and they were then dried for 24 hours in a 90 °C oven. The final weight (Wf) was measured after drying the sample, and the moisture content was calculated using the following formula:
Water absorption
The ASTM D570-98 method was adapted to test the water absorption of bioplastics. 1.5 X 1.5 cm2 bioplastic samples were dried in an oven at 90 °C for 24 hours to get their initial dry weight, which was then estimated gravimetrically using an electronic weighing balance (Wi). After that, the samples were immersed in 40 mL of distilled water for 24 hours at 26 ± 2 °C. After 24 hours, the residual bioplastic was recovered by filtering with filter paper and its weight was gravimetrically (Wf) measured once again. The following equation was used to determine water absorption:
Water solubility
Sanyang et al.24 approach was used to assess the water solubility behaviour of the bioplastic sample. Samples having a surface area of 1.5 × 1.5 cm2 were dried in a 90 °C oven for 24 hours before being gravimetrically weighed with an electronic weighing balance (Wi). The samples were then placed in beakers with 40 mL of distilled water, sealed, and stored at a temperature of 26 ± 2 °C for 24 hours. The residual bioplastics were collected after 24 hours by filtering using filter paper, dried in an oven at 90 °C for 24 hours, and their final weight was calculated using gravimetric analysis (Wf). The following equation was used to calculate the bioplastic sample solubility: water, sealed them, and stored for 24 hours at a temperature of 26 ± 2 °C .
Alcohol solubility
According to Sanyang et al. 24, solubility in alcohol was assessed using the methodology as described in water solubility, with the exception that the samples were put in closed test tubes with 2 mL of ethanol rather than water. The following equation was used to determine the bioplastic sample solubility:
Thickness swelling
It was possible to quantify the thickness swelling of biodegradable film during the measuring of water absorption by determine and recording the thickness of the specimen before and after soaking the samples at room temperature for 24 hours.
Mechanical properties
The material’s tensile strength and Young’s modulus were determined using a Universal testing machine (Lloyd Instruments LF Plus) and a modified version of ASTM D882-91. The samples were cut into rectangular strips 80 mm long and 15 mm wide with scissors. The gauge was kept at 40 mm long and 15 mm wide, with the crosshead speed set at 10 mm/min. Prior to each trial, the thickness of the specimens was measured. At normal room temperature and humidity (73°F, 50%), standard operating procedures were followed. Using the instrumental data, the tensile strength and Young’s modulus of the samples were calculated.
Test for biodegradability
Tensile strength and Young’s modulus of the material were determined using a Universal testing machine (Lloyd Instruments LF Plus) using a modified version of ASTM D882-91. Using scissors, the samples were cut into rectangular strips 80 mm long and 15 mm wide. The gauge was fixed at a length of 40 mm and a width of 15 mm, with the crosshead speed set to 10 mm/min. Before each trial, the thickness of the specimens was measured. At typical room temperature and humidity (73°F, 50%), the standard operating procedure was used. The instrumental data was used to calculate the tensile strength and Young’s modulus of the samples. After 5 days, the residual samples were removed from the soil, cleaned with distilled water, and dried in an oven at 90 °C for 24 hours before undergoing a second gravimetrical computation to determine their ultimate weight (Wf). The bioplastics’ biodegradability, or percentage weight loss, was calculated using the equation below.:
Fourier transform infrared spectroscopy (FTIR)
The chemical structure of the bioplastic materials were determined using a Fourier Transform Infrared Spectrophotometer (FTIR) (IRTracer-100, Shimadzu). The wave-number spanned from 4000 to 650 cm-1, with a resolution of 2 cm-1.
Data analysis
The acquired data was integrated and evaluated using a 2 by 3 factorial complete randomized design. The treatment of level of significance was determined using Analysis of Variance (ANOVA). Duncan’s Multiple Range Test (DMRT) was performed to determine how the means differed from one another.
Results and discussion
Description of biodegradable film
The biodegradable film is made from Sorghum bicolor (L.) starch, and glycerol (Figure 1). The biodegradable film was made by heating it for 15 minutes at 80oC until it gelatinized. The heated mixture was spread on glass and petri plates and allowed to sit for 3-4 days at 17oC in an air-conditioned setting.
Figure 1: Biodegradable fruit bag made from
Sorghum bicolor (L.) starch, and glycerol.
Click here to View Figure
Density
Table 1 demonstrates that decreasing the amount of starch and the percentage of glycerol enhanced the mean density of the film. This is comparable with Moore et al. 25 density measurements for keratin films using varied glycerol concentrations, which ranged from from 0.92 to 1.10 g cm-3.
Table 1: Density of biodegradable film.
Starch (g)
Glycerol (%)
25.0
30.0
40.0
Mean
5.0
1.73
1.02
1.15
1.30
10.0
1.06
0.99
1.13
1.06
Mean
1.40
1.01
1.14
Note: Means that do not share a letter differ substantially by DMRT at the 0.05 level of significance.
Water absorption
Table 2 shows that whereas 10 g of starch with varied percentages of glycerol increased water absorption, 5 g of starch with varying percentages of glycerol decreased water absorption. This is because starch, which has a low moisture content, absorbs more water 26.As a result of glycerol’s strong attraction to water molecules, plasticized samples often exhibit low water absorption values 27. This action can be explained by glycerol forming a stronger hydrogen bond with starch, preventing water molecules from interacting with the plasticizer or starch.
Table 2: Percent water absorption of biodegradable film.
Starch (g)
Glycerol (%)
25.0
30.0
40.0
Mean
5.0
57.48a
71.32bc
55.72a
61.51
10.0
87.53c
63.85b
76.49c
75.96
Mean
72.51
67.59
66.11
Note: Means not sharing letter in common differ significantly at 0.05 level of significance by DMRT
Thickness swelling
Thickness swelling (TS) is an important parameter that captures the stability performance of the composite. Because of the visco-elasticity of the polymer matrix, swelling rates for polymer matrix composites are typically low during the early stages of moisture absorption 28.
Table 3 shows that as glycerol levels increased, the percentage of thickness swelling decreased. The swelling thickness of 10 g starch with 25% glycerol was greater, but the swelling thickness of 10 g starch with 40% glycerol was the least.
Table 3: Thickness swelling of biodegradable film.
Starch (g)
Glycerol (%)
25.0
30.0
40.0
Mean
5.0
43.29b
47.45b
19.26a
36.66
10.0
60.54c
45.83b
10.72c
39.03
Mean
51.92
46.64
14.99
Note: Means not sharing letter in common differ significantly at 0.05 level of significance by DMRT
Tensile strength and elongation
Table 4 displays the tensile strength (Mpa) and elongation (%) of biodegradable film. At 10 g starch and 40% glycerol, the biodegradable film had the highest tensile strength (Mpa), with a value of 9.97. This is due to the high density of cross-linking reactions in starch films between hydroxyl groups and cross-linking agents 29. The highest % elongation, on the other hand, was attained at 5 g. Yamak 30, attributes the decrease in tensile strength to a lack of inter-facial adhesion between the starch and polymer.
Table 4: Tensile strength and percent elongation at break of biodegradable film.
Level of
Starch
Level of
glycerol
Max. stress,
Mpa
% Elongation
25%
4.13
HuaWei Product Page
19.85
5 g Starch
30%
3.09
21.73
40%
3.17
23.84
25%
3.16
20.07
10 g Starch
30%
6.13
16.83
40%
9.97
13.98
Test of biodegradability
After one week of biodegradability testing, the Sorghum bicolor (L.) starch and glycerol-based biodegradable film decomposed by 71.13%. Current biodegradation results for Sorghum bicolor (L.) starch-based bioplastics are consistent with those reported by Mohan et al., 31. The biodegradability of a bioplastic is determined by physical and chemical properties such as surface area, hydrophilicity or hydrophobicity, chemical structure, and molecular weight 32.
Fourier transform infrared spectroscopy
Fourier transform infrared spectroscopy (FTIR) was used to investigate the functional groups present in the bio-plastic samples to see if the addition of plasticizers resulted in the production of any new functional groups. In all of the samples studied, the bio-plastics were found to have distinctive peaks ranging from 2610 to 3490 cm-1 (Fig 2). The addition of plasticizer resulted in the formation of additional peaks at 3032-3416 cm-1. In unplasticized materials, three to four distinctive peaks in the 890-1412 cm-1 range were found.
Figure 2: FTIR of Sorghum bicolor (L.) starch bioplastic without plasticizer (MC) and Plasticized Sorghum bicolor (L.) starch bioplastic (MCB)
Click here to View Figure
FTIR is a commonly used analytical technique for analyzing molecular structures, determining component interactions, and detecting functional groups in a substance 33.The presence of starch was responsible for the usual peaks in the samples analyzed, which ranged from 2900-3010 cm-1 (=C-H stretching). Kumirska et al. 34 investigated characteristic peaks within this range previously. As previously reported, the addition of plasticizer resulted in the formation of additional peaks at 3216-3419 cm-1, which are indicative of the O- H functional group. The presence of these peaks can be attributed to the presence of a large number of hydroxyl groups in both glycerol and polyols, resulting in a broad peak ranging between 3600 and 3200 cm-1 35. This shows that adding a plasticizer to bio-plastics can result in the addition of new functional groups. Three to four typical peaks in the range of around 970-1034 cm-1, showing the C-O-C functional group, and 1025-1145 cm-1, indicating the C-O-H functional group, were found in all unplasticized and plasticized samples of all types. Many previous studies have reported the occurrence of distinctive peaks due to C-O bond stretching between 990 and 1200 cm-1 36.
The FTIR spectra can be used to study interactions between bioplastic components. If the bioplastic components do not blend effectively, no changes may be noticed in the spectra, however some changes can be seen if the components blend properly.
Conclusion
Corn starch from Sorghum bicolor (L.) is a viable component in the manufacturing of biodegradable films. The biodegradable film based on Sorghum bicolor (L.) maize starch and glycerol had the lowest density, water absorption, and thickness swelling of 0.99 g cm-3, 55.72%, and 10.72%, respectively. The maximum tensile strength and elongation obtained are 9.97MPa and 23.84%, respectively. The amount of glycerol used influences the film’s elasticity. A higher glycerol level increases tensile strength while decreasing elongation. The Sorghum bicolor (L.) starch and glycerol-based biodegradable film decomposed by 69.23% after one week of biodegradability testing.
Acknowledgment
We would like to express our gratitude to Afe Babalola University for allowing us to use their laboratory, equipment and instruments, and experimental area.
Conflict of Interest
The authors do not have any conflict of interest.
Funding Source
There was no financial assistance for the author(s)’ research, authorship, or publishing of this work.
References
This work is licensed under a Creative Commons Attribution 4.0 International License.
A PROCESS FOR THE PREPARATION OF
BIODEGRADABLE PLASTIC FILMS
Field of the Invention
The present invention refers in general to the field of biodegradable plastic materials, and more precisely it refers to a novel, improved process for the preparation of biodegradable plastic films, entirely carried out in aqueous environment and starting from vegetal wastes.
State of the Art
Further to a growing environmental awareness of the public opinion and to the economic motivations of industry to find increasingly advantageous ways to reuse waste materials in a cost-effective way, in the last decades great efforts have been made in research to find new ways to recycle waste materials.
The purpose of these studies is to contribute to a sustainable economy, with new industrial processes in which, starting from a waste material, materials with a certain usefulness can be obtained as raw materials: in this way, a virtuous economic cycle is created, wherein a new useful material is obtained from a waste material. In order for the cycle to be truly virtuous, however, the new processes must also be sustainable in themselves, therefore they should not use polluting reagents, nor create polluting wastes on their turn, or even consume large quantities of energy or of raw materials.
These general principles also apply to food wastes, both domestic and industrial, which in industrialized countries have reached levels that are no longer acceptable, so that laws have already been enacted that should put a stop to wastes and encourage re-use.
Currently dehydrated vegetal wastes, such as radicchio leaves, carrot wastes and parsley or cauliflower stalks, are disposed of by incineration, by composting, or they used as fillers in the manufacture of animal food. Moreover, the Applicant themselves have in the past developed a process for processing such vegetal wastes into biodegradable plastic films, thus proposing a sort of valorisation of these waste products, having great potential applications.
This process disclosed in WO 2015/063700, however, involved the use of a very strong halogenated organic solvent, the trifluoroacetic acid (TFA), for solving the starting plant materials. The use of TFA is problematic because of its corrosive and oxidizing power, which makes it difficult using the large volumes required to produce the material in a great amount. Just because of its strength, the materials themselves are partially oxidised and degraded. Furthermore, the proposed process of dissolution in TFA of the plant wastes is very slow, and get to completion within a few days. In addition, TFA is a high-boiling solvent, therefore it is more difficult to eliminate any residue from the final product, which therefore cannot be used for instance in food. Finally, more generally speaking, the use of polluting solvents requiring a particular treatment such as TFA, makes the cost of the process higher, thus also making it more difficult to scale up the process for industrial purposes.
Always starting from plant waste, processes carried out in an aqueous environment are also known, but these are processes having the purpose of obtaining pectins from vegetal wastes that are particularly rich in pectins. These are processes of extraction of pectins, in particular from apple scraps or lemon peels, and they are not processes of conversion of a vegetal waste into another product, as can be a plastic film. Therefore, in these known processes, only a part of the starting wastes, up to a maximum of 30%, can be recovered and appreciated in the extract obtained, however in the form of powder, without the possibility to obtain a complete reuse of the waste mass.
To date, as far as the Applicant is aware, a process of reuse of vegetal waste materials such as those mentioned above, which can be carried out entirely in an aqueous environment and yields valuable products, as can be a biodegradable plastic, has not yet been developed.
Summary of the Invention
The present invention aims therefore to provide a novel process carried out entirely in an aqueous environment that allows obtaining biodegradable plastic films, starting from vegetal wastes.
A particular subject of the present invention is to provide a process of the above said type that is environmentally sustainable and guarantees the absence of any harmful residue in the final product, for example a residue of organic solvent, so that the final product can be considered in its turn an edible product such as the starting materials are.
A still further subject of the present invention is to provide a process that is rapid in obtaining the final product and does not require reagents, solvents and / or operating conditions involving high costs and difficulties in the industrial scaling up of the process.
A still further subject of the present invention is to provide a process that does not cause any degradation or oxidation of the starting material, but preserves on the contrary its properties in the plastic film obtained at the end of the process.
A still further subject of the present invention is to provide a process for the preparation of a product that can be easily mixed with monomers, macromolecules, fillers, functional products or water-soluble particles, or used to create composites on substrates such as paper or fabrics, so as to expand the characteristics of the film that can be obtained also widening further its applications.
These and further subjects are achieved by the process for the preparation of biodegradable plastic films according to the invention, whose essential characteristics are defined in the claim 1 here attached.
Further important features of the process according to the present invention are defined in the dependent claims here attached.
Brief Description of the Figures
Further features and advantages of the process according to the invention will be more clearly illustrated in the following description of exemplary, non-limiting embodiments thereof with reference to the attached figures, wherein:
- Figure 1 : in the pictures from A) to E) film samples are showed obtained respectively in the following Examples from 1 to 5;
- Figure 2: in the figures from A) to D) are illustrated the diagrams tensile stress/tensile strain by extension obtained for the films prepared according to the following Examples 1-4;
- Figure 3: shows the diagrams stress/strain by extension obtained for the films prepared according to the following Examples 1 , 7 and 8; - Figure 4: shows the diagrams stress/strain by extension obtained for the films prepared according to the following Examples 1 and 5;
- Figure 5: shows, in form of histogram, the percentage of anti-oxidant activity detected for the film prepared in the following Example 6 and, by comparison, for the starting material used for preparing the film;
- Figure 6: shows the trend over time of the contact angle measured for the different films prepared as described in the following Examples 1-4 and 7;
- Figure 7: shows the trend over time of the contact angle measured for the different films prepared as described in the following Examples 8-1 1.
Detailed Description of the Invention
The present invention provides a process for the manufacture of a biodegradable plastic film starting from a vegetal waste material, which consists of the following steps:
i) dissolution at a temperature lower than 50°C of the waste material in form of a powder in an aqueous solution of hydrochloric acid, optionally added with acetic acid, wherein the total concentration of acid is equal to or lower than 5% by weight;
ii) transfer the solution obtained in step i), optionally filtered or centrifuged and/or subjected to dialysis against pure water, in a casting mould and evaporation of the aqueous solution coming from the previous step.
The dissolution in step i) can be carried out in any suitable container, preferably equipped with stirring so as to assist dissolution of the material. At temperature lower than 50°C a complete dissolution of the pulverised waste material was observed in times significantly shorter than for the known processes, in any case shorter than 18 hours.
According to an embodiment of this process, the time required for a complete dissolution of the waste material in the aqueous solution ranges between 1 and 18 hours, and preferably it is of approximately 6 hours.
According to a particular embodiment of the process of the invention the temperature in step i) of the present process ranges between 15 and 40°C.
According to a preferred embodiment of the process of the invention the temperature in step i) of the present process is the room temperature.
The waste material used as starting material in the process of the present invention can for instance comprise wastes or a surplus of edible plants; non-limitative examples of these plants are carrots, radicchio, parsley and cauliflower. Further non- limitative examples of these edible plants are broccoli, tomato peel, coconut shells and spinach waste. This waste material is in powder form, typically consisting of particles having size comprised between 10 and 500 micrometres. A size for the powder outside of this range, in particular a smaller size, may anyway be used in the process. The present waste material in form of a powder can be previously dried before being dissolved in the aqueous solution, for example by a simple drying treatment following exposure to air.
In the present invention, by the expression "waste material" it is meant any vegetal material that was not previously subjected to any treatments, in particular to a purifying treatment, but a material that was just powdered and optionally dried at least partially. According to a preferred embodiment this vegetal material may comprise up to approximately 62% (mol) of cellulose, up to approximately 35% (mol) of pectin, up to 15% (mol) of hemicellulose and up to 30% (mol) of other components such as polyesters or fat materials.
According to the invention the concentrations of the starting material can be comprised for instance between 0.1 and 20 % by weight with respect to the weight of the aqueous solution. The preferred concentration of the starting material for implementing the present process ranges between 4 and 10% by weight with respect to the weight of the aqueous solution. Depending on the kind of material, any person having ordinary skills in the art will be able anyway to select and modulate the concentration of the starting material also outside of the above said range, so as to achieve the dissolution thereof under the conditions of the present process and prepare a solution having a suitable viscosity for the subsequent step of casting.
The amount of hydrochloric acid, and optionally of acetic acid too, in water for the dissolution of the waste material in step i) of the invention process is overall equal to or lower than 5% by weight, but it may vary in the range between 0.01 and 10% by weight, obtaining however an acceptable dissolution degree of the starting material. According to an embodiment of the present invention, the ratio between HCI and acetic acid in the aqueous solution in step i) of the process of the invention ranges between 100: 1 and 1 :50, for instance is equal to 1 : 10.
Once the solution is obtained, it is transferred in the casting mould for the step ii) of the present process; these moulds can be moulds suitably shaped, made of glass, of ceramic material, or of non-adhesive plastic material, and inside them, by evaporation of the aqueous solution, the plastic films are obtained. The evaporation in step ii) is carried out under ambient conditions too.
In some embodiments, the solution obtained in step i) can be previously filtered or centrifuged in order to eliminate possible vegetal materials not dissolved, before being subjected to casting.
In other particularly preferred embodiments of the present process, the solution coming from step i) is subjected to dialysis against pure water before being subjected to casting in the subsequent step; this allows to eliminate all traces of the acids used in the first step of the process and to obtain a film simply by casting directly from a pure water solution. On the other hand, this operation did not compromise the characteristics of stability and mechanical resistance of the film subsequently obtained, as shown in the experimental part that follows.
The final product in the form of a so obtained film does possess elasticity, good stability and mechanical properties, as showed below in the experimental part, and it can be subsequently subjected to various kinds of processings, including colouring, decoration, waterproofing treatments, etc. or used to form composites on substrates such as paper or fabrics.
According to a particular embodiment, which allows modulating the hydrophobic characteristics, the film obtained as described above is subjected to washing by immersion of the film in water for a time more or less long depending on the degree of hydrophobicity required for the film. This washing with water, by dissolving the soluble substances present on the film, such as the sugars, increases the hydrophobicity of the film.
The process of the present invention allows therefore obtaining plastic films having a good mechanical strength, starting from vegetal waste materials that would normally be destined for composting or incineration, and this is achieved without using any organic solvent, any chemical reagent or reaction's condition that could degrade the starting material, or create damages to the environment and / or leave harmful residues in the final product. In particular, the present process has proved to be capable of maintaining unaltered the anti-oxidant properties of the starting material.
Furthermore, the process of the invention does not require a large consumption of energy or expensive reagents, and it can be easily scaled up in industry, thus representing an ideal route for waste materials to be recycled.
Finally, as mentioned above, to the solution to be subjected to casting products of different types may be added, such as monomers, macromolecules, fillers, functional products or water-soluble particles, they do not compromise the formation of the final plastic film, but on the contrary their characteristics are expanded so that their applications are further widen.
The following experimental examples are herein reported for non-limitative, illustrative purposes of the present invention.
EXAMPLE 1
Carrot pomace, dried and reduced to powder form, was dispersed in a 5% aqueous solution of HCI in amount equal to 40 mg of pomace per ml of solution. This dispersion was maintained at room temperature for 18 hours, thus obtaining a solution that was then subjected to casting and a film showed in Figure 1A) was obtained.
The so obtained bioplastic film of carrot pomace was characterized by analysis of its composition, which resulted composed by cellulose for 61 % (mol), by pectin for 28% (mol), by hemicellulose for 8% (mol) and by aliphatic polyesters (C16) for 3% (mol).
EXAMPLE 2
The same preparation under the same operative conditions of time and temperature indicated above in Example 1 , and with the same concentration of starting material in the 5% aqueous solution of HCI, was repeated with parsley wastes, previously dried and reduced into powder form. The film obtained by casting from the solution is showed in Figure 1 B).
The so obtained bioplastic film of parsley wastes was characterized by analysis of the composition, which resulted 48% (mol) cellulose, 31 % (mol) pectin, 15% (mol) hemicellulose and 6% (mol) aliphatic polyesters (C16). EXAMPLE 3
The same preparation under the same operative conditions of times and temperatures indicated above in the Example 1 , and with the same concentration of starting material in the 5% aqueous solution of HCI, was repeated with radicchio wastes, previously dried and reduced into powder form. The film obtained by casting from the solution is showed in Figure 1 C).
The so obtained bioplastic film of radicchio wastes was characterized by analysis of the composition, which resulted 44% (mol) cellulose, 34% (mol) pectin, 4% (mol) hemicellulose and 18% (mol) aliphatic polyesters (C16).
EXAMPLE 4
The same preparation under the same operative conditions of times and temperatures indicated above in the Example 1 , and with the same concentration of starting material in the 5% aqueous solution of HCI, was repeated with cauliflower pomace, previously dried and reduced into powder form. The film obtained by casting from the solution is showed in Figure 1 D).
Similarly, films were prepared by casting of solutions starting from pomace wastes of broccoli, spinach, tomato peel and coconut shells.
The so obtained bioplastic film of cauliflower wastes was characterized by analysis of the composition, which was 46% (mol) cellulose, 24% (mol) pectin, 9% (mol) hemicellulose and 21 % (mol) aliphatic polyesters (C16).
EXAMPLE 5
The same preparation, under the same operative conditions of times and temperatures of Example 1 , and with the same concentration of starting material, was repeated starting from dried carrot pomace in powder form, dispersed in a 5% aqueous solution of HCI and acetic acid, in a HCI : acetic acid ratio of 1 : 10, and left for 18 hours at room temperature before casting. The film obtained by casting from the solution is showed in Figure 1 E).
EXAMPLE 6
The same preparation of Example 1 was repeated with the same concentration of carrot waste, previously dried and reduced into powder form, dispersed in the 5% aqueous solution of HCI, but preparing the film by casting of the solution after 6 hours at room temperature.
EXAMPLE 7
The same preparation under the same operative conditions of times and temperatures indicated above in Example 1 , and with the same concentration of carrot pomace previously dried and reduce in powder form in the 5% aqueous solution of HCI, was repeated by subjecting though the solution to dialysis before casting.
EXAMPLE 8
The film of Example 1 obtained by carrot waste was subjected to a treatment of washing with water by immersion of the film in water for about 20 minutes. This washing treatment, besides removing any acidic residue, also causes the dissolvement of all hygroscopic components contained in the film, such as sugars, salts, etc., making the film itself more hydrophobic, as showed in the following.
EXAMPLE 9
The film of Example 2 obtained from parsley waste was subjected to a treatment by washing with water by immersion of the film in water for about 20 minutes.
EXAMPLE 10
The film of Example 3 obtained from radicchio waste was subjected to a treatment by washing with water by immersion of the film in water for about 20 minutes.
EXAMPLE 11
The film of Example 4 obtained from cauliflower waste was subjected to a treatment by washing with water by immersion of the film in water for about 20 minutes.
EXAMPLE 12 - Study of the mechanical properties of the films
The films obtained as described above in the Examples 1-4 have been subjected to tensile tests in order to evaluate their mechanical properties. The mechanical properties have been characterised by cutting specimens according to ISO UNI EN Standard 527-2 5A from the films of the various materials, and by measuring the stress-strain curves according to ISO UNI EN Standard 527-3 with a dual column testing instrument INSTRON 3365.
In the Figures 2 A), 2 B), 2 C) and 2 D) the stress/strain diagrams obtained for the tested films are illustrated: for each of the four different vegetal starting materials Figure 2 shows a diagram with three samples 1-3 that are three replications of the same material to also show the statistical variability in the properties of the material. The measured values for the Young's modulus, the tensile strain (extension) and the tensile stress are summarised in the Table 1 below for the different films prepared starting from different waste materials.
Table 1
For the films obtained from carrot pomace and cauliflower pomace particularly surprising results have been observed in terms of tensile strength, comparable to those of commercial plastic films manufactured with polymers such as LDPE (Low Density Poly Ethylene).
Further tests of mechanical tensile strength have been carried out on the films obtained from carrot pomace, in order to evaluate the possibility of modulating, during the film preparation, the mechanical properties of the film obtainable, making it more or less rigid or plastic. In particular, the tensile tests described above were repeated in parallel, as well as on the film of carrot pomace obtained as described in the Example 1 , and on the films prepared according to the procedures of the Examples 7 and 8. The results are illustrated in the graph of Figure 3.
Further tensile strength tests were carried out according to the procedures described above also on the film obtained as in the Example 5 and in parallel on the film obtained in the Example 1 , finding that the two films - that obtained with the aqueous solution of hydrochloric acid and that obtained with an aqueous solution wherein part of the hydrochloric acid is replaced by acetic acid - have an analogous behaviour. The results of the tests are showed in Figure 4. EXAMPLE 13 - Study of the antioxidant activity of the carrot films
On the film prepared as described above in the Example 6 and in parallel, by comparison, on a sample of the starting material consisting of pomace waste carrot, the antioxidant activity was evaluated by the protocol described by Sharma O.P and Bhat, T.K. "DPPH antioxidant assay revisited", Food Chem. 2009, 113, 1202-1205. The results obtained in such tests, illustrated in Figure 5, indicate a substantial maintenance of the antioxidant activity of the starting material in the film obtained with the present process too.
EXAMPLE 14 - Measurement of the films contact angle
The films prepared according to the procedure described above in the
Examples 1-4 and 7-11 have been subjected to the characterization of the contact angle by means of measuring the angle between the liquid-solid and the liquid-air interface in a water drop poured from a syringe on the film surface, by using an instrument OCA-20 manufactured by DataPhysics. For the various films of the invention the variation over time of the contact angles was measured, whose trend is showed in the graphs of Figures 6 and 7. By comparing these two figures, it can be seen how in general the contact angles increase for all the films going from a film obtained according to the Examples 1-4 to a same film that was also subjected to a washing post-treatment after casting according to the Examples 8-1 1. This increase is particularly relevant for the films obtained from cauliflower wastes, for which the washing transforms the film from hydrophilic into hydrophobic. In this regard, it is recalled that, by convention, the surfaces having contact angles with water greater than 90° are defined as hydrophobic, and the surfaces having contact angles with water smaller than 90° are hydrophilic.
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The present invention was described herein with reference to a preferred embodiment. It is to be understood that other embodiments may exist which belong to the same inventive core, as defined by the scope of protection of the claims set forth in the following.
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