Eco-friendly natural rubber latex and modified starch-based adhesive for wood-based panels application- A review

The use of formaldehyde-based synthetic adhesives for the development of wood-based panels has increased rapidly in the industry. Synthetic adhesives are regarded as a threat to human health and a pollutant because they emit formaldehyde's carcinogenic gas. The breakthrough has prompted to seek for a long-term solution to the formaldehyde threat with natural resources. There has been a significant rise in bio-based adhesive technology and development in the wood-based panel industry. The current review article is intended to present the potentials and the drawbacks of the development of bio-adhesives from sustainable resources such as natural rubber latex (NRL) and starch. This review also discussed the chemical modification and crosslinkers of starch to improve water resistance and adhesion properties. Moreover, this article discusses the compatibility of modified rice starch and NRL for their conclusive applications as wood-based panels adhesive. The findings suggested that bio-based adhesives could replace more synthetic-based adhesives with comparable performance in the near future.

Valorisation of Posidonia oceanica Sea Balls (Egagropili) as a Potential Source of Reinforcement Agents in Protein-Based Biocomposites

Nanocrystalline cellulose (NC) and a lignin-containing fraction (LF) were obtained from egagropili, the so called sea balls produced from rhizome and stem fragments of Posidonia oceanica that accumulate in large amounts along the coastal beaches in the form of tightly packed and dry materials of various dimensions. Both egagropili fractions have been shown to be able to improve the physicochemical properties of biodegradable films prepared from protein concentrates derived from hemp oilseed cakes. These materials, manufactured with a biodegradable industrial by-product and grafted with equally biodegradable waste-derived additives, exhibited an acceptable resistance with a still high flexibility, as well as they showed an effective barrier activity against water vapor and gases (O2 and CO2). Furthermore, both NC and LF decreased film moisture content, swelling ability and solubility, thus indicating that both additives were able to improve water resistance of the hydrocolloid films. The exploitation of egagropili, actually considered only an undesirable waste to be disposed, as a renewable source of reinforcing agents to blend with different kinds of polymers is suggested.

Durability and Strength Characteristics of Casein-Cemented Sand with Slag

Casein is often used as an eco-friendly wood adhesive. In this study, we used casein for soil cementation by mixing it with Jumunjin sand, sodium hydroxide (SH), and calcium hydroxide (CH) as a standard casein formula. The modified casein binder with different proportions of SH and CH was applied to improve water resistance. Furthermore, a blast furnace slag (BFS) was additionally mixed and reacted with alkalinity of modified casein binder. Thus, three types (standard, modified, and modified + BFS, referred to as STD, MOD, and MBS, hereafter) of casein binders were tested for durability and strength of casein-cemented sand. A piezoelectric sensor was installed within each sample to determine the curing time of the casein-cemented samples. The samples were air-cured at room temperature for seven days and some were repeatedly immersed in water thrice. Unconfined compression and jar slake tests were carried out to evaluate the strength and durability of the casein-cemented sand. Also, the microstructure was analyzed using a scanning electron microscope (SEM). We observed variations of peak conductance and corresponding frequency converged as the curing time increased. It was most significant for the MBS samples, which developed strength early. The unconfined compressive strength (UCS) of the air-cured samples was higher than those repeatedly immersed in water due to wash-off of the casein binder. The UCS of the dry MBS sample was 9900 kPa while that of the immersed sample was 430 kPa, which gradually decreased to 60 kPa upon repeated immersion. The samples with STD and MOD had no resistance to durability and showed cracks on the surface, while the MBS sample exhibited significantly improved durability and no cracks. We found that the MBS binder had a positively significant effect on the durability and strength of casein-cemented sand.

Synthesis of Lignin-Based Polyacid Catalyst and Its Utilization to Improve Water Resistance of Urea–formaldehyde Resins

In this study, a lignin-based polyacid catalyst was synthesized via two steps to enhance water resistance of urea–formaldehyde (UF) resins. The first steps involved a hydroxymethylation reaction to increase the hydroxyl content in lignin. Then, hydroxymethylated lignins were reacted with maleic anhydride to form maleated lignin-based polyacids. The acid groups were expected to function as acid catalysts to catalyze the curing process of UF resin. In order to elucidate the structural variation, 3-methoxy-4-hydroxyphenylpropane as a typical guaiacol lignin structural unit was used as a model compound to observe the hydroxymethylation and the reaction with maleic anhydride analyzed by 1H and 13C NMR. After the structural analysis of synthesized lignin-based polyacid by FTIR and 13C NMR, it was used to produce UF resin as an adhesive in plywood and medium density fiberboard (MDF) production, respectively. The results showed that when the addition of lignin-based polyacid was 5% in plywood, it could effectively improve the water resistance of UF resins as compared to commercial additive NH4Cl. It also exhibited a lower formaldehyde emission. Like plywood, lignin-based catalysts used in medium density fiberboard production could not only maintain the mechanical properties, but also inhibit the water adsorption of fiberboards.

Cellulose fiber based fungal and water resistant insulation materials

The development of thermal insulation materials from sustainable, natural fibrous materials is desirable. In the present study, cellulose fiber based insulation foams made of bleached chemi thermo mechanical pulp (CTMP) have been investigated. To improve water resistance, the foams were impregnated with hydrophobic extractives from the outer bark of birch (Betula verrucosa) and dried. The surface morphology of the foams and the distribution of the deposited particles from the extractives were observed by scanning electron microscopy (SEM). The modified foams showed improved water resistance, as they did not disintegrate after immersion in water for 7 days, whereas the unmodified foam did. Compared to the unmodified foam, the modified foams absorbed 50% less moisture within 24 h. The modification had no negative effects on the thermal insulation properties, fungal resistance or compressive strength of the foams. The proposed approach is simple and can be easily integrated into plants working based on the biorefinery concept.