Development of a new production method for a polypropylene-clay nanocomposite

The role of interface on the toughening and failure mechanisms of thermoplastic nanocomposites reinforced with nanofibrillated rubber

The interface plays a crucial role in the physical and functional properties of polymer nanocomposites, yet its effects have not been fully recognized in the setting of classical continuum-based modeling. In the present study, we investigate the roles of interface and interfiber interactions on the toughening effects of rubber nanofibers embodied in thermoplastic-based materials. Emphasis is placed on establishing comprehensive theoretical and atomistic descriptions of the nanocomposite systems subjected to pull-out and uniaxial extension in the longitudinal and transverse directions. Using the framework of molecular dynamics, the annealed melt-drawn nanofibers were spontaneously formed via the proposed four-step methodology. The generated nanofibers were then crosslinked using the proposed robust topology-matching algorithm, through which the chemical reactions arising in the crosslinking were closely assimilated. The interfiber interactions were also examined with respect to separation distances and nanofiber radius via a nanofiber-pair atomistic scheme, and the obtained results were subsequently incorporated into the pull-out and uniaxial test simulations. The results indicate that the compatibilizer grafting results in enhanced interfacial shear strength by introducing extra chemical interactions at the interface. In particular, it was found that the compatibilizer restricts the formation and coalescence of nanovoids, resulting in enhanced toughening effects. Together, we have shown that the presence of a small amount of well-dispersed rubber nanofibrillar network whose surfaces are grafted with maleic anhydride compatibilizer can dramatically increase the toughness and alter the failure mechanisms of the nanocomposites without any deterioration in the stiffness, which is also consistent with the recent experimental observations in our lab. The interfacial failure mechanism was also investigated by monitoring the changes in the atomic concentration profiles, mean square displacement and fractional free volume. The results obtained may serve as a promising alternative for the continuum-based modeling and analysis of interfaces.

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

Concerns of petroleum dependence and environmental pollution prompt an urgent need for new sustainable approaches in developing polymeric products. Biobased polymers provide a potential solution, and biobased nanocomposites further enhance the performance and functionality of biobased polymers. Here we summarize the unique challenges and review recent progress in this field with an emphasis on self-assembly of inorganic nanoparticles. The conventional wisdom is to fully disperse nanoparticles in the polymer matrix to optimize the performance. However, self-assembly of the nanoparticles into clusters, networks, and layered structures provides an opportunity to address performance challenges and create new functionality in biobased polymers. We introduce basic assembly principles through both blending and in situ synthesis, and identify key technologies that benefit from the nanoparticle assembly in the polymer matrix. The fundamental forces and biobased polymer conformations are discussed in detail to correlate the nanoscale interactions and morphology with the macroscale properties. Different types of nanoparticles, their assembly structures and corresponding applications are surveyed. Through this review we hope to inspire the community to consider utilizing self-assembly to elevate functionality and performance of biobased materials. Development in this area sets the foundation for a new era of designing sustainable polymers in many applications including packaging, construction chemicals, adhesives, foams, coatings, personal care products, and advanced manufacturing.

A Review of Wet Compounding of Cellulose Nanocomposites

Cellulose nanomaterials (CNs) are an emerging class of materials with numerous potential applications, including as additives or reinforcements for thermoplastics. Unfortunately, the preparation of CNs typically results in dilute, aqueous suspensions, and the lack of efficient water removal methods has hindered commercialization. However, water may also present opportunities for improving overall efficiencies if its potential is better understood and if it is better managed through the various stages of CN and composite production. Wet compounding represents one such possible opportunity by leveraging water's ability to aid in CN dispersion, act as a transport medium for metering and feeding of CNs, plasticize some polymers, or potentially facilitate the preparation of CNs during compounding. However, there are also considerable challenges and much investigation remains. Here, we review various wet compounding approaches used in the preparation of cellulose nanocomposites as well as the related concepts of wet feeding and wet extrusion fibrillation of cellulose. We also discuss potential opportunities, remaining challenges, and research and development needs with the ultimate goal of developing a more integrated approach to cellulose nanocomposite preparation and a more sophisticated understanding of water's role in the compounding process.

Influence of Processing Conditions on the Preparation of Clay-Based Nanocomposites by Twin-Screw Extrusion

This review paper is devoted to the preparation of clay-based thermoplastic nanocomposites by melt blending in a twin-screw extruder. The influence of the main processing parameters (screw speed, feed rate, barrel temperature, screw profile) on the state of the clay dispersion at the micro- and nanoscale is characterized. The change of dispersion state along the screws and the corresponding mechanisms are presented. The interest of process modelling to predict the state of dispersion is evaluated and, finally, the main modifications of the twin-screw extrusion process to improve the clay dispersion are reviewed.

Ionizing radiation: a versatile tool for nanostructuring of polymers

Very high energies of particulate (accelerated electrons, swift heavy ions) or electromagnetic wave (γ-, X-rays) radiation can be used to initiate free radical based reactions in solids, liquids or gases. Because of non-selectivity of absorption of X-rays, γ rays and accelerated electrons in matter free radicals are generated homogeneously in the bulk material. These free radicals on the polymers or monomers are used extensively in the synthesis and modification of polymeric materials. The unique properties of ionizing radiation make it a very useful tool in the top-down and bottom-up synthesis of nanomaterials. In this article the utilization of ionizing radiation in the form of swift heavy ions, accelerated electrons, X- and γ rays will be described for development of advanced materials by radiation-induced grafting in nanoscale, synthesis of polymeric nanoparticles, radiation-assisted synthesis of nanogels and nanocomposites. The properties difficult to be attained by other techniques will be described by giving examples for the cases of ion track-etched membranes, fuel cell membranes, sensors, detectors, cell culture media, polymer thin films embedded with metal nanoparticles, polymer/clay nanocomposites with a prospect for the future outlook.

Effects of chitin nanowhiskers on the thermal, barrier, mechanical, and rheological properties of polypropylene nanocomposites

Incorporation of chitin nanowhiskers into polypropylene shows improvements in both water barrier and mechanical properties.

Water-Assisted Production of Thermoplastic Nanocomposites: A Review

Water-assisted, or more generally liquid-mediated, melt compounding of nanocomposites is basically a combination of solution-assisted and traditional melt mixing methods. It is an emerging technique to overcome several disadvantages of the above two. Water or aqueous liquids with additives, do not work merely as temporary carrier materials of suitable nanofillers. During batchwise and continuous compounding, these liquids are fully or partly evaporated. In the latter case, the residual liquid is working as a plasticizer. This processing technique contributes to a better dispersion of the nanofillers and affects markedly the morphology and properties of the resulting nanocomposites. A survey is given below on the present praxis and possible future developments of water-assisted melt mixing techniques for the production of thermoplastic nanocomposites.

Toughening, Thermal Stability, Flame Retardancy, and Scratch–Wear Resistance of Polymer–Clay Nanocomposites

Addition of a small percent of clay to polymers improves their stiffness, strength, dimensional stability, and thermal, optical, and barrier properties. Improvements are often attributed to the availability of large numbers of clay nanolayers with tremendous interfacial area. Despite the positive effects from the addition of clay, there are unresolved issues, such as embrittlement, thermal stability, flame retardancy, scratch–wear response of the resultant nanocomposites, and/or achieving a balance between different mechanical and physical properties. In this review, we discuss these issues and the approaches that have been adopted in the expectation of resolving and understanding them, with particular emphasis on our recent and current research.