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Agricultural waste residues (agro-waste) are the source of carbohydrates that generally go in vain or remain unused despite their interesting morphological, chemical, and mechanical properties. With rapid urbanization, there is a need to valorize this waste due to limited non-renewable resources. Utilizing agro-waste also prevents the problems like burning and inefficient disposal that otherwise lead to immense pollution worldwide. In addition, conversion of biomass to value-added products like earthen cups, weaving baskets, and bricks is equally beneficial for the rural population as it provides secondary income, creates jobs, and improves rural people's lifestyles. This review paper will discuss an overview of different applications utilizing agro-waste residues. In particular, agro-wastes used as construction material, bio-fertilizers, pulp and paper products, packaging products, tableware, heating applications, biocomposites, nano-cellulosic materials, soil stabilizers, bioplastics, fire-retardant additive, dye removal, and biofuels will be summarized. Finally, several commercially available agro-waste products will also be discussed, emphasizing the circular economy.

The emulsification of biowaxes in an aqueous environment is important to broaden their application range and make them suitable for incorporation in water-based systems. The study here presented proposes a method for emulsification of carnauba wax by an in-situ imidization reaction of ammonolysed styrene (maleic anhydride), resulting in the encapsulation of the wax into stabilized organic nanoparticles. A parameter study is presented on the influences of wax concentrations (30 to 80 wt.-%) and variation in reaction conditions (degree of imidization) on the stability and morphology of the nanoparticles. Similar studies are done for encapsulation and emulsification of paraffin wax as a reference material. An analytical analysis with Raman spectroscopy and infrared spectroscopy indicated different reactivity of the waxes towards encapsulation, with the bio-based carnauba wax showing better compatibility with the formation of imidized styrene (maleic anhydride) nanoparticles. The latter can be ascribed to the higher functionality of the carnauba wax inducing more interactions with the organic nanoparticle phase compared to paraffin wax. In parallel, the thermal and mechanical stability of nanoparticles with encapsulated carnauba wax is higher than paraffin wax, as studied by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical analysis. In conclusion, a stable aqueous emulsion with a maximum of 70 wt.-% encapsulated carnauba wax was obtained, being distributed as a droplet phase in 200 nm organic nanoparticles.

An increase in population compels the textile industry to expand production to fulfill the apparel requirement, resulting in huge textile waste. These wastes are managed either by landfilling or incineration processes, which negatively contribute to the environment. Converting waste into value-added products is essential to reducing environmental pollution and thereby achieving a circular economy through proper waste management practices. This paper provides a comprehensive overview of different categories and forms of textile waste, their source of generation, the reusing capability of the textile industry, other valorization potentials in different fields, and various challenges associated with their valorization practices. This review presents textile wastes as the raw material source for preparing different value-added products such as in manufacturing textiles, packaging materials, plastics, composites, construction applications, energy generation, chemical additives, composting, and several other applications.

Ceramic foam materials have received great attention in recent years for their light weight, thermal/electrical insulation, high crack tolerance and good machinability properties. However, some applications demand higher mechanical strength, better resistivity of the surface against mechanical impact or improved abrasion resistance. In this paper, the feasibility of dip coating 89 vol% porous, green alumino-silicate foam bars with dimensions in the centimeter range was studied and a dip coating route was proposed. The surface morphology of uncoated and coated foam bars was first analyzed by scanning electron microscopy (SEM) and later detailed using the GelsightTM method. Mechanical properties were determined by 4-point bending. A dense coating layer with a uniform thickness and good interfacial adhesion was obtained over the foam. Consequently, a three-fold increase in the flexural strength was measured for coated parts. In addition, the versatility of the developed dip coating route was demonstrated coating samples of bigger size like panels as well as complex geometries like cylindrical crucibles.

In this study, a biodegradable film from bacterial biopolymer, i.e., poly (3-hydroxybutyrate-co-4-hydroxybutyrate) or P(3HB-co-4HB) incorporating Thyme essential oil as an antimicrobial agent was developed as an active packaging for shelf-life extension of bread. Thin solvent-cast films containing 10, 20, and 30% v/w of Thyme oil were prepared and studied for the morphological, thermal, chemical, mechanical, barrier, and antimicrobial behaviors. The presence of oil in P(3HB-co-4HB) films and their purity without detectable remains of solvent, i.e., chloroform, was confirmed by infrared spectroscopy. In parallel, the time-bound release of volatile Thyme oil from the films was demonstrated when stored in a controlled environment. The plasticizing effect of Thyme oil in films was evidenced by decreased tensile strength and crystallinity. In contrast, an increase in elongation at break and water vapor permeability of oil films were measured. Finally, the antimicrobial activity of oil films was checked against total bread molds and observed that when bread was sealed in P(3HB-co-4HB) films containing 30% v/w Thyme oil, its shelf-life extended to at least 5 days compared to 1–4 days for the neat film.

After successful preparation of master batch formulations including polyhydroxybutyrate (PHB) and fibrillated cellulose additives, the compositions with different types and concentrations of fillers were used for the deposition of a coating on packaging paper grades, by using compression moulding in a hydraulic press. The resulting paper coatings are considered to provide a green solution for the production of protective barrier layer films with tunable hydrophobicity and oxygen barrier resistance. The processing of the nanocomposites into flat and homogeneous coatings was optimized for different conditions of moulding temperature and times, in particular, the flow conditions of the coating under pressing in contact with the substrate strongly depends on the presence of fillers. The effects of filler types on adhesion of the coating at the paper/polymer interface were investigated and the poor adhesion of native PHB coatings was tremendously improved after hydrophobic surface modification of the nanocellulose fillers. The inclusion of a wax and nanoparticles attached to the nanocellulose fiber surface enhanced the flowing properties of the coating by eliminating fiber agglomeration in contact with the paper substrate and reducing the effects of fiber pull outs. Therefore, hydrophobic fiber modification is necessary to obtain a homogenous dispersion during compressing moulding of coating materials for paper applications. Furthermore, the effect of processing on the final crystallinity of the master batches, films and paper coatings is presented by considering the reduction in degree of crystallinity for coatings in contact with a paper substrate owing to the surface confinement of crystallization processes. On the other hand, also the time-effects of secondary crystallization of the coatings as a function of aging time were lower for the coatings as compared to the free-standing films, in relation with the reduction of molecular mobility of the polymer chains under confined conditions.

In this work, the intrinsic drawbacks of polyhydroxybutyrate (PHB) such as slow crystallization rate, secondary crystallization and brittle nature were improved by blending with bio-based fillers, i.e. nanofibrillated/microfibrillated cellulose (NFC/MFC). A novel chlorinated-solvent-free based system was developed to blend PHB and NFC/MFC that resulted in homogenous dispersion of fibers in the PHB matrix, without the need for surface modification of fibers. The developed nano/micro-composite materials were fabricated as masterbatch pellets and films. Additionally, the effect of different NFC/MFC fiber morphologies influencing the crystallization behaviour of PHB was investigated in detail by differential scanning calorimetry, polarized optical microscopy and Fourier transform infrared spectroscopy. Both non-isothennal and isothermal crystallization studies (modelled with Avrami's kinetics) were performed on nanocomposites and variations in crystallization kinetics of PHB after addition of NFC/MFC were determined. Addition of NFC/MFC resulted in the drastic increase in the crystallization rate of PHB and hence they acted as nucleating agents. The fine and homogeneous morphology of NFC produced smaller PHB spherulites and restricted the growth of secondary crystals, hence resulted in more flexible films than PHB or PHB-MFC films, as determined by the mechanical testing of films. The more heterogeneous morphology of MFC altered the PHB crystallization mechanism most, as seen from the distorted shape of PHB spherulites along with the higher Avrami exponent, i.e. n >= 3. This work was financially sponsored by the Junioprofessorenprogram Baden-Wurttemberg 'Functional Bio-based Nano-Coating for Paper Applications"('NaCoPa'-project 2012-2015) and the Robert Bosch Foundation in the framework of the Juniorprofessorenprogram 'Sustainable use of Natural Materials' ('Foresnab'-project 2011-2016). Rastogi, VK (reprint author), Aalto Univ, Sch Chem Technol, Dept Bioprod & Biosyst, Vuorimiehentie 1, Espoo 02150, Finland. vibhore.rastogi@aalto.fi

The thermal release properties of soy oil from poly(styrene- co -maleimide) nanoparticles containing 50 wt% encapsulated oil have been quantified as a function of temperature and time. The effects of different synthesis conditions on the thermal stability of the nanoparticles and their oil release have been evaluated, i.e., by gradually increasing the amount of ammonium hydroxide used for the imidization of poly(styrene- co -maleic anhydride). First, the intrinsic thermal properties of the oil-filled nanoparticles were analysed by differential scanning calorimetry, which revealed an exothermal reaction related to the oil release and a suppression of the glass transition that may be masked owing to the complex structure of the hybrid nanoparticles. The isothermal scans showed different rates of oil release after a post-imidization reaction. The oil release was better followed by dynamic mechanical analysis, which illustrated changes in visco-elastic properties expressed by the maximum in the loss factor that related to the amount of released oil. Depending on the amount of ammonium hydroxide, the oil started to release below the glass transition temperature at various rates. Thermal release profiles of the oil were quantified by infrared and Raman spectrocopy after heating for 2 min to 6 h at 125 to 250 °C, based on variations in oil-related and imide-related absorption bands. The oil release increased below and above the glass transition temperature, following a parabolic trend, and progressively decreased at higher ammonium hydroxide concentrations, in parallel with higher imide content and changes in imide conformation. The kinetics and mechanism of the oil release can be described by the Korsmeyer–Peppas model, suggesting a dominating diffusion mechanism that is influenced by further imidization of the polymer matrix during heating.

Surface modification of micro- and nanofibrillated cellulose (MFC and NFC) under aqueous environment was performed by deposition of poly(styrene-co-maleimide) nanoparticles synthesized by imidization of poly(styrene-co-maleic anhydride) in presence of wax and ammonium hydroxide in variable amounts. Specifically, the influences of fiber fibrillation on nanoparticle formation (i.e., reaction efficiency) and permanent nanoparticle deposition on the fiber surface (i.e., retention) were investigated. The surface modification was mainly governed by the fiber diameter, surface charges and amount of wax. As such, the MFC affected the imidization reaction to a smaller extent (i.e., high reaction efficiency) and was more densely deposited by nanoparticles than NFC (i.e., high retention). Moreover, wax protected the fibers against fibrillation and peeling-off at high temperature and favored nanoparticle deposition. As a result, water contact angles of 142° were obtained for modified MFC in parallel with a surface coverage of 92%.

Although films of microfibrillated cellulose (MFC) have good oxygen barrier properties due to its fine network structure, properties strongly deteriorate after absorption of water. In this work, a new approach has been followed for actively tuning the water resistance of a MFC fiber network by the inclusion of dispersed organic nanoparticles with encapsulated plant wax. The modified pulp suspensions have been casted into films and were subsequently cured at 40 to 220 °C. As such, static water contact angles can be specifically tuned from 120 to 150° by selection of the curing temperature in relation with the intrinsic transition temperatures of the modified pulp, as determined by thermal analysis. The appearance of encapsulated wax after curing was followed by a combination of morphological analysis, infrared spectroscopy and Raman mapping, showing balanced mechanisms of progressive release and migration of wax into the fiber network controlling the surface properties and water contact angles. Finally, the appearance of nanoparticles covered with a thin wax layer after complete thermal release provides highest hydrophobicity.

The use of microfibrillated cellulose is mainly constraint by its hydrophilic character, and there is an urgent search for sustainable alternatives towards hydrophobic surface modification. Here, we present a production technique where cellulose fibers are modified by an in-situ reaction with styrene maleic anhydride, ammonium hydroxide and plant wax under aqueous environment. After imidization, the cellulose fibers were fibrillated along with partial coverage of the surface by styrene maleimide nanoparticles and incorporation of wax, resulting in the formation of a stable and hydrophobic micro-porous fiber network.