A review on polymer–layered silicate nanocomposites

The preparation of carboxymethylated microfibrillated cellulose (MFC) films by dispersion-casting from aqueous dispersions and by surface coating on base papers is described. The oxygen permeability of MFC films were studied at different relative humidity (RH). At low RH (0%), the MFC films showed very low oxygen permeability as compared with films prepared from plasticized starch, whey protein and arabinoxylan and values in the same range as that of conventional synthetic films, e.g., ethylene vinyl alcohol. At higher RH’s, the oxygen permeability increased exponentially, presumably due to the plasticizing and swelling of the carboxymethylated nanofibers by water molecules. The effect of moisture on the barrier and mechanical properties of the films was further studied using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. The influences of the degree of nanofibrillation/dispersion on the microstructure and optical properties of the films were evaluated by field-emission scanning electron microscopy (FE-SEM) and light transmittance measurements, respectively. FE-SEM micrographs showed that the MFC films consisted of randomly assembled nanofibers with a thickness of 5–10 nm, although some larger aggregates were also formed. The use of MFC as surface coating on various base papers considerably reduced the air permeability. Environmental scanning electron microscopy (E-SEM) micrographs indicated that the MFC layer reduced sheet porosity, i.e., the dense structure formed by the nanofibers resulted in superior oil barrier properties.

Oxygen and oil barrier properties of microfibrillated cellulose films and coatings

Cellulose nanocrystals are unique nanomaterials derived from the most abundant and almost inexhaustible natural polymer, cellulose. These nanomaterials have received significant interest due to their mechanical, optical, chemical, and rheological properties. Cellulose nanocrystals primarily obtained from naturally occurring cellulose fibers are biodegradable and renewable in nature and hence they serve as a sustainable and environmentally friendly material for most applications. These nanocrystals are basically hydrophilic in nature; however, they can be surface functionalized to meet various challenging requirements, such as the development of high-performance nanocomposites, using hydrophobic polymer matrices. Considering the ever-increasing interdisciplinary research being carried out on cellulose nanocrystals, this review aims to collate the knowledge available about the sources, chemical structure, and physical and chemical isolation procedures, as well as describes the mechanical, optical, and rheological properties, of cellulose nanocrystals. Innovative applications in diverse fields such as biomedical engineering, material sciences, electronics, catalysis, etc, wherein these cellulose nanocrystals can be used, are highlighted.

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Cellulose nanocrystals: synthesis, functional properties, and applications.

Flexible barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect-free monolayers are impermeable to all atoms and molecules. However, it has been proved to be challenging to develop large-area defectless graphene films suitable for industrial use. Here we report barrier properties of multilayer graphitic films made by gentle chemical reduction of graphene oxide laminates with hydroiodic and ascorbic acids. They are found to be highly impermeable to all gases, liquids and aggressive chemicals including, for example, hydrofluoric acid. The exceptional barrier properties are attributed to a high degree of graphitization of the laminates and little structural damage during reduction. This work indicates a close prospect of graphene-based flexible and inert barriers and protective coatings, which can be of interest for numerous applications.

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Impermeable barrier films and protective coatings based on reduced graphene oxide

In modern society, polymer packaging plays a critical role in the preservation and distribution of perishable goods such as food and prescription medicines. [ 1 , 2 ] Since the effectiveness of poly mer packaging materials in preventing product degradation is directly dependent upon their impermeability to degradative gases [ 3 ] and their opacity to high-energy light, [ 4 ] signifi cant efforts have been devoted to improving these properties. [ 5 ]

Crumpled graphene nanosheets as highly effective barrier property enhancers.

The barrier solutions presently available on the market all have their drawbacks, e.g. cost, water-sensitivity, opacity or perceived environmental bad-will. At the same time there is a trend to use more plastic-based packaging materials for different applications, e.g. as replacements for metal and glass containers. This situation has stimulated the industry to provide new, more efficient barrier solutions. The innovations go along five major lines: (a) thin, transparent vacuum-deposited coatings; (b) new barrier polymers as discrete layers; (c) blends of barrier polymers and standard polymers; (d) organic barrier coatings; and (e) nanocomposite materials. This paper provides a comprehensive review of the different approaches, outlining the principle behind each barrier technology, its performance, its potential and the companies developing and producing the materials. Copyright © 2003 John Wiley & Sons, Ltd.

Recent innovations in barrier technologies for plastic packaging—a review

Three different techniques for experimentally determining the bending stiffness of flexible films and laminates have been evaluated using a number of different packaging materials. The results showed that a cantilever test was the best, giving reliable data for all kinds of films and laminates. A three-point bending test proved to be sensitive to misalignment, whereas a bending-under-own-weight test was incapable of handling curled samples and generally gave lower stiffness values. A model for predicting the bending stiffness of multilayer laminates from the elastic modulus of the constituents was developed and used to examine the influence of layer position and composition on the overall bending stiffness. Model calculations showed that thin layers, such as adhesives, print and barrier coatings, can have a large influence on the bending stiffness and that the influence often goes against what would be intuitively expected. The calculations also showed that layer modulus often is less important than layer thickness and that the position of the layer in the laminate can have a major influence on the overall stiffness. Copyright © 2001 John Wiley & Sons, Ltd.

Predicting and determining the bending stiffness of thin films and laminates

The limited mechanical resistance of flexible packaging materials means that they are prone to puncturing during processing and transport. The present work is concerned with food powder packaging, where defects between 0.5 and 1 mm in size have been detected. According to a generally accepted model for water vapour transport through large pores, defects of this size should strongly compromise the barrier properties of the packaging. In spite of this, no significant deterioration of the product has been observed, implying either that the standard model is wrong or that the water transport is inhibited by other phenomena. A study was undertaken to elucidate the mechanism of water absorption through pores into a dehydrated soup product. The first part of the study examined the water diffusion through model pores, using gravimetric measurements with silica gel as absorbing medium. The results show that the standard model gives predictions of at best 2 and at worst 20 times too high. Another model, published 25 years prior to the standard model but then largely forgotten, was found to agree well with experimental data. The second part of the study involved the use of magnetic resonance imaging to visualize the mechanism of water absorption in the product. It was found that the absorption proceeded in two independent steps. First, the powder next to the pore quickly absorbed water, and then the water spread evenly throughout the bulk at a much slower rate.

Water vapour transport through large defects in flexible packaging: modeling, gravimetric measurement and magnetic resonance imaging

For paper-based dry pet food packaging, one of the main requirements is a high resistance against staining from the fat in the product. For both development and quality control, rapid and reliable standardized test procedures assessing this property are needed. Although a number of tests are available, they either apply only to certain types of packaging materials and show limited correlation with field behaviour, or employ non-standard testing substances, long testing times and complicated equipment. In response to this situation, a new testing procedure that reflects field behaviour but without the drawbacks of the existing tests has been developed. The new test shows high reproducibility and good correlation with field performance for a wide range of multiwall bag and folding box materials with different types of grease resistance treatment. Copyright © 2002 John Wiley & Sons, Ltd.

J. Lange

Papers

Recent innovations in barrier technologies for plastic packaging—a review

Predicting and determining the bending stiffness of thin films and laminates

Water vapour transport through large defects in flexible packaging: modeling, gravimetric measurement and magnetic resonance imaging

Novel method for testing the grease resistance of pet food packaging

Erratum to ‘Predicting and determining bending stiffness of thin films and laminates’1

J. Lange

Papers

Recent innovations in barrier technologies for plastic packaging—a review

Predicting and determining the bending stiffness of thin films and laminates

Water vapour transport through large defects in flexible packaging: modeling, gravimetric measurement and magnetic resonance imaging

Novel method for testing the grease ­resistance of pet food packaging

Erratum to ‘Predicting and determining bending stiffness of thin films and laminates’1

Novel method for testing the grease resistance of pet food packaging