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.

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.

The purpose of the study was to develop a less hydrophilic, and therefore more useful, material from orange waste produced in large quantities by the food industry. A new derivative of industrial orange waste was synthesized via esterification with maleic anhydride. The reaction was confirmed via Fourier transform infrared spectroscopy (FTIR), and the degree of substitution of the hydroxyl groups was 0.39 ± 0.01, as determined by a back-titration method. A major change in physical structure was confirmed by scanning electron microscopy (SEM). The flake-like structure of orange waste changed to a sponge-like structure after the reaction, which involved an increased volume and a reduced density by approximately 40%. The sponge-like structure was represented as an agglomeration of particles with a low specific surface area of 2.18 m2/g and a mean pore diameter of 10.7 nm. Interestingly, the grafted orange waste seemed to become more hydrophobic, which was confirmed by a contact angle test; however, the material absorbed more water vapor. Thermogravimetric analysis (TGA) confirmed a thermally more uniform, though, less heat-resistant material. This work suggests a possible way of utilizing orange waste via synthesizing a renewable material with possible applications as a filler in biocomposites.