Novel In-situ Precipitation Process to Engineer Low Permeability Porous Composite

Recent advancements, trends, fundamental challenges and opportunities in spray deposited cellulose nanofibril films for packaging applications

Plastic packaging is causing a serious environmental concern owing to its difficulty in degrading and micro-particulates' emissions. Developing biodegradable films has gained research attention to overcome ecological and health issues associated with plastic based packaging. One alternative substitute for petroleum-based plastic is nanocellulose based films, having distinguishing characteristics such as biodegradability, renewability, and non-toxicity. Nanocellulose is classified into three major types, i.e., cellulose nanofibril, cellulose nanocrystals, and bacterial nanocellulose. However, the scope of this review is limited to cellulose nanofibril (CNF) because this is the only one of major types that could be turned into film at a competitive cost with petroleum derived polymers. This paper provides a concise insight on the current trends and production methods of CNF. Additionally, the methods for transforming CNF into films are also discussed in this review. However, the focus of this review is the CNF films produced via spray deposition, their properties and applications, and fundamental challenges associated with their commercialization. Spray deposition or spray coating is an ideal candidate as a large-scale production technique of CNF films due to its remarkable features such as rapidity, flexibility, and continuity. Spray deposited CNF films exhibit excellent mechanical properties and oxygen barrier performance, while, possessing limited moisture barrier performance. The possible pathways to improve the moisture barrier performance and optical properties of these films are also discussed in this review. The existing publications on spray deposited CNF films are also highlighted from the literature. Finally, the current status of industrial production of these films and opportunities for academics and industries are also presented, indicating that fibre production capacity needs to be enhanced.

Effects of In-Situ Filler Loading vs. Conventional Filler and the Use of Retention-Related Additives on Properties of Paper

In the present paper, aspects concerning the obtained and characterization of additive systems used for maximizing filler retention, and the effects on paper properties, were investigated. The effects of retention additives over properties of paper, containing fibers from in-situ loading (IS-CCP), were analyzed against the effects of additives over properties of paper containing fibers from conventional loading, obtained by the addition of calcium carbonate in precipitated form (CCP). The physico-mechanical properties were analyzed by various analyses and investigations: calcium carbonate content, X-ray diffraction, scanning electron microscopy (SEM) images, optical and mechanical properties, in order to develop the best systems of retention additives for obtaining higher retention loads for making paper with high content of nano-filler material. The obtained results reveal that at the same level of calcium carbonate content, all paper samples with in-situ loading had higher the optical and mechanical properties than the paper obtained by conventional loading in all cases the additives studied. For all studied properties, nanoparticles had a positively influence over paper properties.

Lignin Particles for Multifunctional Membranes, Antioxidative Microfiltration, Patterning, and 3D Structuring

We introduce a new type of particle-based membrane based on the combination of lignin particles (LPs) and cellulose nanofibrils (CNF), the latter of which are introduced in small volume fractions to act as networking and adhesive agents. The synergies that are inherent to lignin and cellulose in plants are re-engineered to render materials with low surface energy (contact angle measurements) and can be rendered water-resistant with the aid of wet-strength agents (WSAs). Importantly, they are most suitable for antioxidative separation (ABTS^•+ radical inhibition): membranes with uniform porous structures (air permeability and capillary flow porosimetry) allow effluent oxidation at 95 mL/cm², demonstrating, for the first time, the use of unmodified lignin particles in flexible membranes for active microfiltration. Moreover, the membranes are found to be nonfouling (protein adhesion and activity rate). The inherent properties of lignin, including UV radiation blocking capacity (UV transmittance analysis) and reduced surface energy, are further exploited in the development of tailorable and self-standing architectures that are almost entirely comprised of nonbonding LP (solids content as high as 92 w/w%). Despite such composition, the materials develop high toughness (oscillatory dynamic mechanical analysis), owing to the addition of minor amounts of CNF. Multifunctional materials based on thin films (casting), 3D structures (molding), and patterned geometries (extrusion deposition) are developed as a demonstration of the potential use of lignin particles as precursors of new material generation. Remarkably, our observations hold for spherical LPs since a much poorer performance was observed after using amorphous powder, indicating the role of size and shape in related applications.

Sustainable Barrier System via Self-Assembly of Colloidal Montmorillonite and Cross-linking Resins on Nanocellulose Interfaces

Cellulose nanofibrils (CNFs) are able to form strong oxygen-barrier films suitable for food packaging but lack the needed water resistance in comparison to plastics. Desired water barrier quality can be achieved by applying mineral additives within the nanofibrils network. In current contribution, a sustainable hybrid system with an improved water barrier function is proposed by incorporating colloidal montmorillonite nanoclay (MMT) and two cross-linking agents, namely, polyamidoamine epichlorohydrin (PAE) and Acrodur thermoset acrylic resin (ACR) into CNF interfaces. Continuous matrices were produced via evaporation-induced self-assembly of colloidal building blocks followed by appropriate heat-curing regime to impart internal cross-linking. The development of chromophore functionalities and formation of ester motifs on the hybrid matrix (with no evidence of degradation) were detected by Fourier-transform infrared (FT-IR) spectroscopy. Intercalation of clay, solely, reduced the water vapor transmission rate (WVTR) to some extent; however, a more remarkable decline (by 60%) was observed upon the curing and cross-linking process. In fact, combination of clay platelets and cross-linkers contributed to a denser film structure and restricted water passage. Also, an excellent resistance to oil and grease was observed in all the studied films (Kit number of 11). A reduction in tensile strengths and resistance to cracking at fold was noted and ascribed to MMT interference in cellulose interchain hydrogen bonds. This however was counteracted by the introduction of cross-linkers, apparently by aiding stress transfer within the matrix. MMT imparted a limited elevation in the surface free energy, pointing out to an induced hydrophilicity; however, surface energy values declined markedly upon using cross-linkers. Finally, thermal stability of hybrids was adversely affected, compared to neat CNFs. Our study suggests the potential utilization of low-cost, sustainable biobarrier films for application in food/drug packaging, where low permeation of moisture is highly desirable.