Extensive quantities of apple pomace are generated annually but its disposal is still challenging. This study addresses this issue by introducing a new, environmentally-friendly approach for the production of sustainable biomaterials from apple pomace, containing 55.47% free sugars and a water insoluble fraction, containing 29.42 ± 0.44% hemicelluloses, 38.99 ± 0.42% cellulose, and 22.94 ± 0.12% lignin. Solution casting and compression molding were applied to form bio-based films and 3D objects (i.e., fiberboards), respectively. Using glycerol as plasticizer resulted in highly compact films with high tensile strength and low elongation (16.49 ± 2.54 MPa and 10.78 ± 3.19%, respectively). In contrast, naturally occurring sugars in the apple pomace showed stronger plasticizing effect in the films and resulted in a fluffier and connected structure with significantly higher elongation (37.39 ± 10.38% and 55.41 ± 5.38%, respectively). Benefiting from the self-binding capacity of polysaccharides, fiberboards were prepared by compression molding at 100 °C using glycerol or naturally occurring sugars, such as plasticizer. The obtained fiberboards exhibited tensile strength of 3.02–5.79 MPa and elongation of 0.93%–1.56%. Possible applications for apple pomace biomaterials are edible/disposable tableware or food packaging. 

This study was conducted to improve the properties of thin films prepared from orange waste by the solution casting method. The main focus was the elimination of holes in the film structure by establishing better cohesion between the major cellulosic and pectin fractions. For this, a previously developed method was improved first by the addition of sugar to promote pectin gelling, then by the addition of maleic anhydride. Principally, maleic anhydride was introduced to the films to induce cross-linking within the film structure. The effects of concentrations of sugar and glycerol as plasticizers and maleic anhydride as a cross-linking agent on the film characteristics were studied. Maleic anhydride improved the structure, resulting in a uniform film, and morphology studies showed better adhesion between components. However, it did not act as a cross-linking agent, but rather as a compatibilizer. The middle level (0.78%) of maleic anhydride content resulted in the highest tensile strength (26.65 ± 3.20 MPa) at low (7%) glycerol and high (14%) sugar levels and the highest elongation (28.48% ± 4.34%) at high sugar and glycerol levels. To achieve a uniform film surface with no holes present, only the lowest (0.39%) level of maleic anhydride was necessary. 

This study was conducted to improve the properties of thin films prepared from orange waste by the solution casting method. The main focus was the elimination of holes in the film structure by establishing better cohesion between the major cellulosic and pectin fractions. For this, a previously developed method was improved first by the addition of sugar to promote pectin gelling, then by the addition of maleic anhydride. Principally, maleic anhydride was introduced to the films to induce cross-linking within the film structure. The effects of concentrations of sugar and glycerol as plasticizers and maleic anhydride as a cross-linking agent on the film characteristics were studied. Maleic anhydride improved the structure, resulting in a uniform film, and morphology studies showed better adhesion between components. However, it did not act as a cross-linking agent, but rather as a compatibilizer. The middle level (0.78%) of maleic anhydride content resulted in the highest tensile strength (26.65 +/- 3.20 MPa) at low (7%) glycerol and high (14%) sugar levels and the highest elongation (28.48% +/- 4.34%) at high sugar and glycerol levels. To achieve a uniform film surface with no holes present, only the lowest (0.39%) level of maleic anhydride was necessary.

Anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW), leading to renewableenergy production in the form of methane, is a preferable method for dealing with the increasing amountof waste. Food waste is separated at the source in many countries for anaerobic digestion. However, thepresence of plastic bags is a major challenge for such processes. This study investigated the anaerobicdegradability of different bioplastics, aiming at potential use as collecting bags for the OFMSW. Thechemical composition of the bioplastics and the microbial community structure in the AD processaffected the biodegradation of the bioplastics. Some biopolymers can be degraded at hydraulic retentiontimes usually applied at the biogas plants, such as poly(hydroxyalkanoate)s, starch, cellulose and pectin,so no possible contamination would occur. In the future, updated standardization of collecting bags forthe OFMSW will be required to meet the requirements of effective operation of a biogas plant.

To address the current plastic pollution problem, the replacement of conventional plastics with bioplastics can be considered. Although the land use of crop cultivation for bioplastics is still negligible, there is an increasing interest in the utilisation of lignocellulosic waste products for the production of bioplastics. A latest trend in researching sources for bioplastic production focuses on the use of fruit and vegetable wastes because of their versatile polysaccharides. Among different fruit wastes, orange waste and apple pomace have been evaluated as raw materials in this thesis.

The development of biofilms and 3D objects from the above-mentioned raw materials via the solution casting and compression moulding methods was investigated. Biocomposites are generally made from a bioplastic matrix and reinforcement, or a plastic reinforced with natural fibres. In the present study, pectin was used as a matrix, and cellulosic fibres wereused as reinforcement. Orange waste films had an opaque appearance with a yellowish colour and were very flexible, while the 3D objects had brown colour. The films had mechanical properties comparable with those of commodity plastics, such as 32 to 36 MPa tensile strength. The films were biodegradable under anaerobic conditions, and 3D objects showed good biodegradability in soil. Grafting of orange waste with maleic anhydride was performed in order to improve its properties, e.g. the hydrophilicity of the polysaccharides-based materials. Grafting reduced the density by 40 % and increased the hydrophobicity compared with unmodified orange waste. Further improvements included upgrading the film casting method and incorporating maleic anhydride in the recipe. The lowest amount of necessary maleic anhydride was determined (0.4 %), and the resulting films had a smoother and more uniform surface. The original methods were also applied to apple pomace in order to produce films and 3D objects. Films from apple pomace had an elongation of 55 %, a twofold increase compared to that of orange waste films containing maleic anhydride (28 %). Orange waste and apple pomace were also mixed for 3D object fabrication, achieving the highest strength of 5.8 MPa (ratio of 75 to 25, respectively) a threefold increase compared to that achieved with only orange waste alone (1.8 MPa).

The results are promising‚ but further improvements, e.g. in respect to hydrophilicity and upscaling‚ are needed for orange waste and apple pomace to develop into raw materials for next-generation bioplastics.

One third of the cell wall of vascular plants is composed of pectin, which serves as the cementing material for the cellulosic network, behaving as a stabilized gel. Industrially, pectin is produced from juice and sugar production waste. Different sources and extraction conditions result in diversity in characteristics and applications of pectin. Most commonly, pectin is used in the food industry as a gelling and thickening agent and it is favored in the pharmaceutical industry as a carrier for colon-specific drugs. Pectin has good potential to be utilized as a matrix in production of environmentally friendly film packaging as well as biocomposite materials. Pectin is sensitive to chemical reactions and promotes the homogeneous immobilization of cells, genes, and proteins. However, due to limited mechanical properties pectin is not used for structural applications but instead rather for composites in which its biodegradable properties can be utilized. Pectin is often reinforced with hydroxyapatite and biphasic calcium phosphate for bone regeneration and tissue engineering applications. It can also be used as a biosorbent for copper removal from aqueous solutions. Active packaging of nanohybrids composed of pectin and halloysite nanotubes that are loaded with rosemary essential oil is another application of pectin-based composites.

While citrus waste is abundantly generated, the disposal methods used today remain unsatisfactory: they can be deleterious for ruminants, can cause soil salinity, or are not economically feasible; yet citrus waste consists of various valuable polymers. This paper introduces a novel environmentally safe approach that utilizes citrus waste polymers as a biobased and biodegradable film, for example, for food packaging. Orange waste has been investigated for biofilm production, using the gelling ability of pectin and the strength of cellulosic fibres. A casting method was used to form a film from the previously washed, dried, and milled orange waste. Two film-drying methods, a laboratory oven and an incubator shaker, were compared. FE-SEM images confirmed a smoother film morphology when the incubator shaker was used for drying. The tensile strength of the films was 31.67 ± 4.21 and 34.76 ± 2.64 MPa, respectively, for the oven-dried and incubator-dried films, which is within the range of different commodity plastics. Additionally, biodegradability of the films was confirmed under anaerobic conditions. Films showed an opaque appearance with yellowish colour.