Nanocellulose-montmorillonite composites of low water vapour permeability

The effect of pre-treatment and process conditions on the gas barrier properties of fibrillated cellulose films and coatings: A review

Microfibrillated cellulose (MFC) is a bio-material produced by disintegrating cellulose fibres into fibrillar components. MFC could offer a sustainable solution to packaging needs since it can form an excellent barrier to oxygen. However, a comprehensive understanding of how MFC characteristics impact barrier properties of MFC films or coatings is required. This article critically reviews how the extent of separation of fibres into fibrils-and any resulting changes to the crystallinity and degree of polymerisation of cellulose-influences gas barrier properties of MFC films or coatings. Findings from publications investigating the barrier performance of MFC prepared through different processes intending to increase the effectiveness of fibrillation are evaluated and compared. The effects of processing conditions or chemical pre-treatments on barrier properties of MFC films or coatings are then discussed. A comparison of reported results showed that morphology and size polydispersity of the cellulose strongly influence the barrier properties of MFC. However, changing the MFC production process to decrease fibril diameter and polydispersity can result in changes to cellulose crystallinity; reduction in fibril length; introduction of bulky functional groups; or increased fibril surface charge: all of which could have a negative impact on the barrier properties of the final films or coatings.

A Review on Barrier Properties of Cellulose/Clay Nanocomposite Polymers for Packaging Applications

Packaging materials are used to protect consumer goods, such as food, drinks, cosmetics, healthcare items, and more, from harmful gases and physical and chemical damage during storage, distribution, and handling. Synthetic plastics are commonly used because they exhibit sufficient characteristics for packaging requirements, but their end lives result in environmental pollution, the depletion of landfill space, rising sea pollution, and more. These exist because of their poor biodegradability, limited recyclability, etc. There has been an increasing demand for replacing these polymers with bio-based biodegradable materials for a sustainable environment. Cellulosic nanomaterials have been proposed as a potential substitute in the preparation of packaging films. Nevertheless, their application is limited due to their poor properties, such as their barrier, thermal, and mechanical properties, to name a few. The barrier properties of materials play a pivotal role in extending and determining the shelf lives of packaged foods. Nanofillers have been used to enhance the barrier properties. This article reviews the literature on the barrier properties of cellulose/clay nanocomposite polymers. Cellulose extraction stages such as pretreatment, bleaching, and nanoparticle isolation are outlined, followed by cellulose modification methods. Finally, a brief discussion on nanofillers is provided, followed by an extensive literature review on the barrier properties of cellulose/clay nanocomposite polymers. Although similar reviews have been presented, the use of modification processes applied to cellulose, clay, and final nanocomposites to enhance the barrier properties has not been reviewed. Therefore, this article focuses on this scope.

Residual Strain and Nanostructural Effects during Drying of Nanocellulose/Clay Nanosheet Hybrids: Synchrotron X-ray Scattering Results

Cellulose nanofibrils (CNF) with 2D silicate nanoplatelet reinforcement readily form multifunctional composites by vacuum-assisted self-assembly from hydrocolloidal mixtures. The final nanostructure is formed during drying. The crystalline nature of CNF and montmorillonite (MTM) made it possible to use synchrotron X-ray scattering (WAXS, SAXS) to monitor structural development during drying from water and from ethanol. Nanostructural changes in the CNF and MTM crystals were investigated. Changes in the out-of-plane orientation of CNF and MTM were determined. Residual drying strains previously predicted from theory were confirmed in both cellulose and MTM platelets due to capillary forces. The formation of tactoid platelet stacks could be followed. We propose that after filtration, the constituent nanoparticles in the swollen, solid gel already have a "fixed" location, although self-assembly and ordering processes take place during drying.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Review on Hybrid Reinforced Polymer Matrix Composites with Nanocellulose, Nanomaterials, and Other Fibers

The use of composite materials has seen many new innovations for a large variety of applications. The area of reinforcement in composites is also rapidly evolving with many new discoveries, including the use of hybrid fibers, sustainable materials, and nanocellulose. In this review, studies on hybrid fiber reinforcement, the use of nanocellulose, the use of nanocellulose in hybrid forms, the use of nanocellulose with other nanomaterials, the applications of these materials, and finally, the challenges and opportunities (including safety issues) of their use are thoroughly discussed. This review will point out new prospects for the composite materials world, enabling the use of nano- and micron-sized materials together and creating value-added products at the industrial scale. Furthermore, the use of hybrid structures consisting of two different nano-materials creates many novel solutions for applications in electronics and sensors.

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.

Preparation and benchmarking of novel cellulose nanopaper

Synthetic polymers and plastics which are currently used as barrier materials in packaging applications are neither renewable nor biodegradable. Nanopaper, which is obtained by breaking down cellulose fibers into nanoscale particles, have unique properties with the potential to replace synthetic packaging materials, but requires very high energy to mechanically process the fibers into nanopaper. This research investigates whether refining alone can be used to produce nanopaper with sufficient quality for packaging applications. Nanopaper was produced from Bleached Eucalyptus Kraft (BEK) refined with a PFI mill and from Northern Bleached Softwood Kraft (NBSK) refined in a pilot disc refiner. Both trials found a plateau for oxygen permeability and water vapour permeability that was reached after 1800 kWh/t and 12,000 kWh/t for refining in the pilot disc refiner and PFI mill, respectively. Refining beyond these optima produced either little or no reduction in permeability, while increasing the drainage time to form a sheet. However, elastic modulus, strain at break and sheet light transmittance did continue to increase. The plateau oxygen permeability of ~ 1.24 (cc µm)/(m² day kPa) is 1-3 orders of magnitude lower than the oxygen permeability for PET and LDPE, respectively, while the plateau water vapour permeability ~ 3 × 10^-11 g/m.s. Pa was 1-2 orders of magnitude higher than for PET and LDPE. The improved strength and barrier properties of nanopaper achieved at lab and pilot scale mechanical refining process promises a sustainable alternative to conventional packaging.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-022-04563-0.

Rheo-SAXS study of shear-induced orientation and relaxation of cellulose nanocrystal and montmorillonite nanoplatelet dispersions

The development of robust production processes is essential for the introduction of advanced materials based on renewable and Earth-abundant resources. Cellulose nanomaterials have been combined with other highly available nanoparticles, in particular clays, to generate multifunctional films and foams. Here, the structure of dispersions of rod-like cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) was probed using small-angle X-ray scattering within a rheological cell (Rheo-SAXS). Shear induced a high degree of particle orientation in both the CNC-only and CNC:MNT composite dispersions. Relaxation of the shear-induced orientation in the CNC-only dispersion decayed exponentially and reached a steady-state within 20 seconds, while the relaxation of the CNC:MNT composite dispersion was found to be strongly retarded and partially inhibited. Viscoelastic measurements and Guinier analysis of dispersions at the shear rate of 0.1 s^-1 showed that the addition of MNT promotes gel formation of the CNC:MNT composite dispersions. A better understanding of shear-dependent assembly and orientation of multi-component nanoparticle dispersions can be used to process materials with improved mechanical and functional properties.

Assembly of cellulose nanocrystals and clay nanoplatelets studied by time-resolved X-ray scattering

Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d ∝ φ-1/2 scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.

An energy efficient production of high moisture barrier nanocellulose/carboxymethyl cellulose films via spray-deposition technique

Nanocellulose (NC) films are considered as a prospective alternative to non-sustainable packaging materials, however, their higher embodied energy and limited moisture barrier properties are regarded as a huge constraint regarding their commercialization. This study aims to produce films with relatively low environmental impact and improved barrier performance. For this purpose, carboxymethyl cellulose (CMC) and NC were combined, and this resulted in multidimensional advantages. The mass production of films could be achieved in only 2 h (requiring at least 24 h under ambient conditions) when dried in an oven at 75 °C with enhanced mechanical properties and without compromising their dimensional stability. The moisture barrier properties of the NC/CMC films were improved up to 92 % compared with the NC films alone and the results achieved are comparable with packaging materials such as polyethylene terephthalate (PET), polycarbonates (PC) etc. Finally, the NC/CMC (1:1) films have low environmental impact compared with PET films.

Composites of nanofibrillated cellulose with clay minerals: A review

Biopolymers-based composites are, in general, environmentally friendly materials, which can be obtained from renewable sources. Some of them can also present promising properties to be used in food packaging and electronic devices, being thus logical substitutes to petroleum-based polymers, specifically plastics. Cellulose nanofibrils (CNF) obtained by chemical/enzymatic pre-treatments followed by a mechanical treatment appear as a new suitable biomaterial. However, CNF are still quite expensive materials, due to the required chemicals/equipment/energy involved, and additionally, they present some limitations such as high hydrophilicity/high water vapour permeability. The combination of CNF with clay minerals, such as montmorillonite or kaolinite, as widely available geo-resources, represents an excellent way to reduce the amount of CNF used, enabling the production of valuable materials and reducing costs; and, at the same time it is possible to improve the characteristics of the formed materials, such as mechanical, gas barrier and fire retardancy properties, if appropriate conditions of preparation are used. Nevertheless, to obtain hybrid CNF/clay composites with superior properties it is necessary to ensure a good dispersion of the inorganic material in the CNF suspension and a good compatibility among the inorganic and organic components. To fulfil this goal, several strategies can be considered, including physical treatments of the suspensions, CNF and clay surface chemical modifications, and the use of a coupling agent. In this review article, the state-of-the-art on a new emerging generation of composites (films, foams or coatings) based on nanofibrillated cellulose and nanoclay, with focus on strategies for their preparation and most relevant achievements is critically reviewed, bearing in mind their potential application as substitutes for common plastics. A third component has been eventually added to these organic-inorganic hybrids, e.g., chitosan, carboxymethylcellulose, borate or epoxy resin, to enhance specific characteristics of the material. Some general background on the production of different types of CNF and their main properties is previously provided.

Properties of Polylactic Acid Reinforced by Hydroxyapatite Modified Nanocellulose

Polylactic acid (PLA) is one of the most promising bio-based materials, but its inherent hydrophobicity limits its application. Although nanocellulose (NCC) is a desirable reinforcement for PLA, the poor interface compatibility between the two has been a challenge. In this work, hydroxyapatite (HAP) modified NCC was prepared, and the obtained NCC/HAP reinforcement was used to prepare PLA/NCC-HAP composites. Different ratios of NCC to HAP were studied to explore their effects on the mechanical and thermodynamic properties of the composites. When the ratio of NCC to HAP was 30/70, the tensile strength and tensile modulus of the composite film reached 45.6 MPa and 2.34 GPa, respectively. Thermogravimetric analysis results indicate that thermal stability of the composites was significantly improved compared with pure PLA, reaching 346.6 °C. The above revelations show that NCC/HAP significantly improved the interface compatibility with PLA matrix.

An insight into nanocellulose as soft condensed matter: Challenge and future prospective toward environmental sustainability

Nanocellulose, a structural polysaccharide that has caught tremendous interests nowadays due to its renewability, inherent biocompatibility and biodegradability, abundance in resource, and environmental friendly nature. They are promising green nanomaterials derived from cellulosic biomass that can be disintegrated into cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC), relying on their sensitivity to hydrolysis at the axial spacing of disordered domains. Owing to their unique mesoscopic characteristics at nanoscale, nanocellulose has been widely researched and incorporated as a reinforcement material in composite materials. The world has been consuming the natural resources at a much higher speed than the environment could regenerate. Today, as an uprising candidate in soft condensed matter physics, a growing interest was received owing to its unique self-assembly behaviour and quantum size effect in the formation of three-dimensional nanostructured material, could be utilised to address an increasing concern over global warming and environmental conservation. In spite of an emerging pool of knowledge on the nanocellulose downstream application, that was lacking of cross-disciplinary study of its role as a soft condensed matter for food, water and energy applications toward environmental sustainability. Here we aim to provide an insight for the latest development of cellulose nanotechnology arises from its fascinating physical and chemical characteristic for the interest of different technology holders.

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.

Natural Biomaterial-Based Edible and pH-Sensitive Films Combined with Electrochemical Writing for Intelligent Food Packaging

An edible and pH-sensitive film combined with electrochemical writing was developed by using gelatin, gellan gum, and red radish anthocyanins extract for intelligent food packaging. The composite film showed an orange red-to-yellow color change in the pH range of 2-12. The tensile strength, ductility, and barrier abilities to ultraviolet (UV) light and oxygen of the films were improved as the concentration of red radish anthocyanins increased. Multicolor patterns were successfully drawn on the films by using the electrochemical writing method. The composite films, which acted as gas sensors, presented visible color changes in the presence of milk and fish spoilage, while the written patterns were well-preserved. Accordingly, this composite film with written patterns could be an easy-to-use indicator with great potential for monitoring food spoilage as a part of an intelligent packaging system.