2022 Volume 1

Salt hydrate phase change materials (PCMs) have been intensively used for thermal energy storage (TES) due to their sharp melting points, high energy storage density, small volume change and low cost. However, the problems of phase separation, supercooling and relatively low thermal conductivity of salt hydrate PCMs need to be addressed for high-efficiency TES. In this research, cellulose nanofibrils (CNFs) and CNFs-based composites were used to improve the TES performance of sodium acetate trihydrate (SAT). The effect of CNFs on the phase stability of SAT was investigated and the involved mechanism was explored by the rheological study. CNFs/graphene nanoplatelets (GNPs) composites and CNFs/silver nanoparticles (AgNPs) composites were prepared and used to improve the TES efficiency of SAT. Results indicate that adding 0.8% of CNFs to SAT increased the viscosity, enhanced solid-like rheological behaviors by entangled nanofiber network, and successfully eliminated phase separation of SAT. Owing to the excellent dispersing capability of CNFs, the aggregations of GNPs and AgNPs were avoided in the prepared CNFs/GNPs and CNFs/AgNPs composites. The resulting SAT-based composite PCMs were phase-stable and exhibited improved thermal conductivities over pure SAT due to the thermal conductivity enhancers, GNPs and AgNPs. Besides, with the combined use of sodium phosphate dibasic dodecahydrate and CNFs/AgNPs0.02 composite, the supercooling degree of SAT decreased to 1.2 °C. The prepared composite PCMs exhibited reasonable phase change temperature and enthalpy, and improved thermal stability. In summary, green and versatile CNFs based composites were prepared, and they successfully overcame the drawbacks of salt hydrate PCMs for TES applications.

The spreading and adhesion behavior of latex is a crucial factor in determining the structure and properties of the low-latex-content pigment coating layer. In spite of its importance, there has been a lack of analytical techniques to describe these characteristics in a coating layer. This study presents novel parameters and techniques for quantitative analysis of the spreading and adhesion behavior of latex binder in a coating layer, which is based on cross-section SEM image analysis. A comprehensive series of model coating layers were prepared to achieve varying extents of latex spreading. This was prepared by using latices with different glass transition temperatures and various drying or dry-sintering conditions. Parameters were developed to determine and quantify the different morphological characteristics of latices in the coating layers, which had advantages over qualitative observation from the SEM images. Developed analytical techniques were applied to reveal correlations between structural properties and the coating end-use properties, which contributed to a better understanding of coating structure development. A transitional change in coating structure was observed in the low latex spreading domain and this largely influenced the end-use properties of coating layers such as the mechanical properties and light-scattering efficiency. Micro-roughness of the coating surface and gloss were positively correlated to the spreading extent of the latex. It was notable that despite low levels of coating shrinkage due to the low latex content, the micro-roughness still changed with latex spreading variations. Quantitative analysis of latex spreading and mechanical properties of the coating layer also enabled us to separate the adhesion behavior of latex binder into physical and chemical aspects. This would propose a strategy for paper manufacturers to optimize their coated paper products.

There is an ever-increasing interest towards utilizing nanocellulose as barrier coatings and films, with many companies moving towards pilot scale production of nanocellulose to be used primarily for barrier coatings. However, high suspension viscosity and yield stress, poor adhesion to substrates, poor moisture sensitivity, and additional drying infrastructure needed for large-scale processing of nanocelluloses are some of the challenges that need to be addressed before commercialization. The current work aims at understanding and addressing the above challenges and to develop high-throughput continuous processes required to convert nanocellulose suspensions into barrier coatings and films. Rheology of different types of nanocelluloses across a wide range of shear rates is evaluated with special attention on the influence of dispersants (carboxymethyl cellulose (CMC) and Sodium polyacrylate (NaPA)) on the suspension processability and coating quality. A slot-die applicator is used to apply nanocellulose suspensions as a thin layer on a paper substrate in a continuous process. For moisture protection, biodegradable polymers and dispersions are applied onto the nanocellulose-coated paper via extrusion or dispersion coating. The resulting multilayer structure is then evaluated for its barrier properties viz., oxygen, water vapor, mineral oils, and grease at different test conditions. CMC addition reduces the yield stress, increases water retention, and slows down structure recovery (post high-shear) for nanocellulose suspensions, and thus has positive influence on coating quality and barrier properties. A new Casson-power-cross model was proposed to explain the viscosity behavior of cellulose nanofibrils (CNFs) across a wide shear-rate region, and Herchel-Bulkley model explains the viscosity behavior of cellulose nanocrystals (CNCs). Water vapor permeance for multilayer coatings remained below the control single-layer moisture-barrier materials, and oxygen permeance values were similar or lower than that of pure nanocellulose films. Glycerol and sorbitol plasticizers further improve oxygen barrier and kaolin addition improves the adhesion at nanocellulose/thermoplastic interface. The results provide insight into understanding the various factors that influence the continuous processing of a wide variety of nanocellulose suspensions into biodegradable barrier coatings and will pave the way for industrial production of sustainable packaging.

The use of microfibrillated cellulose (MFC) in the paper industry has become established following many years of development by both academic and industrial researchers. Commercial installations typically use mechanical disintegration techniques such as refiners and grinders to convert aqueous suspensions of pulp fibres into a material consisting of fibrils and fibre fragments with diameters ranging from the nanometre to the micron scale. MFC suspensions of a few percent solids content show very high viscosity at low shear rates, but also very significant shear thinning behaviour, rapid viscosity recovery after shear and high filtration resistance. MFC added to paper furnishes at up to 5% by weight functions as a strength additive, enabling increases in mineral filler content, improvements in paper properties, reductions in weight and cost savings across a wide range of paper and board grades. As a complementary technology to pulp refining, addition of MFC offers process flexibility as well as improved wet web strength and runnability, reduced air permeability and increased z-direction strength. Although the fine fibrils of MFC do not dewater easily on their own, when added at low levels to paper their effect on machine drainage can be managed without loss of paper machine speed. In recent years, MFC has attracted much interest as a coating material. Layers or films of pure MFC show near-zero air permeability, high resistance to oil and grease and an effective barrier to organic vapours and oxygen. Mixtures of mineral particles and as little as 15% MFC provide an effective surface for water-intensive printing techniques such as flexography and inkjet. Application of MFC suspensions after the wet line of a papermachine has been demonstrated as a practical solution to obtain coatings, exploiting the rheological behaviour of the MFC to achieve excellent holdout onto a poorly-consolidated sheet, and using the vacuum and press sections of the machine to remove excess water. Further development and commercialisation of this technology, together with low cost MFC production and improved product characterisation, should ensure the continued growth of its use in the paper and board industry.

Mineral fillers are indispensable in many industrial branches and are used in a variety of different materials. In plastic technology they act as a classic extender to lower the costs of the production process but also as “active fillers” to improve the mechanical and optical property profile. In the paper industry, fillers are also used to reduce raw material costs and to adjust the optical as well as surface properties. However, fillers entail the problem that their application quantity is sharply limited. Inorganic fillers show no binding properties. They reduce the product strength with higher use and lead to complications in the further processing of the products (e.g. increased dust propensity during the packaging and printing processes). In order to expand the use of fillers and their positive effects on varying products and to prevent the negative effects of the material in parallel, mineralized cellulosic structures should be created for versatile applications in different branches of industry.

Cell and organoids culture in three-dimensions (3D) gel systems is important from a fundamental aspect for understanding the development and behaviour of body organs, and from a practical perspective for producing cells, tissues and even new organs for bio-medical applications. The cell culture requires a supportive network environment, biological or synthetic, which provides the suitable biological systems (proteins and co-factors), mechanical support (flexible morphology) and chemical composition for cells/organoids to grow, spread and migrate. Current naturally extracted matrices like, Matrigel and collagen, are expensive with poorly defined and variable composition; they are not reliable for common practice 3D organoids culture. To overcome issues with the naturally extracted matrices, researchers have been investigating and developing new synthetic and natural polymer gels as alternatives. Cellulose has emerged as an attractive matrix with strong potential for cell and organ culture in 2D and 3D networks. The inherent natural biocompatibility of cellulose fibres including non toxicity, low cost, and their ability to form flexible gels, provide a compelling alternative to the current limited and expensive animal-based matrices. This review focuses on the recent development of cellulose nano fibres (CNF) based gel matrices for 3D cell and organoids culture. The review highlights how functionalisation of CNF optimizes the gel structure, visco-elastic properties and composition for supporting cell growth, interactions, spreading and migration. The state-of-the-art characterisation methods are discussed to monitor CNF stiffness, strength, morphology and composition, and furthermore, cell culture and their stability in the CNF network. The knowledge gained from this review aims at supporting bioengineers in further developing the potential of CNF gels for different 3D organs culture and tissue engineering applications.

Today, simulation tools and digital twin models have taken a central role in product development at Tetra Pak. As a result, improved functionality and quality are secured in developing new packages, filling, and converting machines. First, an overview is presented on the development of paper models, followed by examples of how the paper models are used with simulation tools at Tetra Pak today. Such as the creasing and filling process related to material defects.

Paperboard is a common material for packages and other carriers of information. During rotary printing processes, the paperboard is subjected to rapid deformations in the out-of-plane direction as it passes through the nip between the rolls of the printer. Being viscoelastic in nature, the mechanical response of the material to high deformation rates differs from what is measured with conventional testing conducted at slower deformation rates. In this work, a device called the rapid ZD-tester is used to show the response of paperboards subjected to a rapid pressure pulse and compare this to measurements made at lower strain rates in a common universal testing machine. All the tested paperboards show complete recovery within 5 s when being rapidly compressed, while the slower compression to the same pressure leaves a deformation that remains after 5 s. The stiffness response differs between the paperboards, but does not consistently increase or decrease between slow or rapid compressions. The difference in response between slow and rapid compression appears larger for the low-density paperboard in the study. The time scales in the rapid ZD-tester are comparable to those in a printing press, and, therefore, evaluation of the material response of the paperboard measured by this device is relevant in the context of printing applications.

The perception of mechanical rigidity when touching a package is important for purchasing decisions. This perception will depend both on the material and geometry of the product packaging, but also on the position where the package is grasped. Both kinaestethic (globally) and cutaneous cues (locally around the fingertip) play a role in the perception of compliance, but cutaneous cues are more important. We therefore use a tactile sensor to investigate the mechanical interaction between the tactile sensor and a cartonboard package; we study the changes depending on the measuring position and the material. Using linear discriminant analysis (LDA) on the measurement result we show that we can separate these two changes for separate analysis.

Tissue is a low-density paper product distinguished by a microscale crepe structure. We investigate the relationship between the macroscale tissue tensile response and crepe structure. We propose a parameter called the Crepe Index (CI) that can be measured from edge images of the creped sheet. Crepe Index correlates very well with the measured tensile failure strain (“stretch”), but its correlation with the measured initial elastic stiffness is unclear. A discrete elastoplastic model (DEM) is developed to explain the experimental results and understand the nonlinearity in the tensile curve. The model accounts for both material nonlinearity through a bilinear elastoplastic constitutive law for the sheet material, and the geometric nonlinearity arising from large deformations. The creped sheet is idealized as a triangular wave of prescribed wavelength and waveheight, with nonlinear bending and stretching effects. The model results show that the tensile response is governed by both the nonlinearity of the sheet material (fibre network) and crepe structure (geometry). The yielding in stretching and bending gives rise to an inflection in the tensile response. It is found that the initial stiffness depends not only on CI, but also on parameters such as sheet thickness to crepe-wavelength ratio, and stiffness of sheet material after creping. Thus, the variability in above parameters can be one of the reason for unclear correlation between measured initial stiffness and CI. For CI range of tested commercial tissues, both experiments and model show that stretch varies linearly with CI, with an almost unity slope and a positive intercept (i.e, stretch> CI). Thus, the overall stretch of creped tissue is a sum of CI and network stretching.