Polymer Hybrids and Composites

Dear Colleagues,

Polymer-based multiphase materials combine properties of constituents depending on morphologies and interfacial bonding. Most efficient functional materials are two-phase because the individual properties are retained, whereas with a single phase or miscible composition, properties tend to be averaged. An example is the need for two phases to optimise strength and toughness. Natural materials have been used as models for synthetic compositions and innovations have evolved in materials selection, mixing and dispersion, morphology formation through processing and self-assembly, and physio-chemistry at interfaces and the surface. Synthetic materials simulating natural materials are called biomimetic materials. Salient to biomimetic materials are physical interactions or chemical bonding between the components. When like-polymers are combined they are called blends. When polymers are combined with other materials they are called composites, and when they are chemically bonded they form a new material called a hybrid. A multiphasic structure assumes that components are immiscible, yet compatible in that they interact favourably at interfaces. Interactions and bonding require uniform dispersion that may include orientation and anisotropic structures. Molecular rigidity, symmetry and dispersed phase shape contribute to packing and orientation.

Dispersed phase(s) could be biomaterials, nano-materials, minerals, synthetic inorganic fillers such as: zeolites, pyrogenic silica or titania, layered clay. Some of these dispersed phases modify processing causing thixotropy, with less emphasis in final product performance. A dispersion modifies the polymer causing: Reinforcement, toughening, dimension scale—surface to volume ratio, aspect ratio—fibers, platelets, and particles. The polymer is a support or binder for the filler that may exhibit: Conductivity, magnetic, bioactive, light sensitive, coloured pigments, and 3D printing materials (filaments). Examples of biomimetic materials, learning or copying from nature are nacre replicas, cellulose skeleton after removing lignin, hemicellulose and pectins, and laminated structures mimicking plant surface membranes. Natural organic fillers from wood are cellulose fibres, nano-fibers, particles, and wood flour. Single component polymer–polymer composites have integrated interfaces, such as all-polypropylene, all-polyethylene or all-poly(ethylene terephthalate). Organic polymers are combined with organo-inorganic (polysiloxane) hybrids and form hybrids with polymeric silsesquioxanes (POSS). Biopolymer composites form with cellulose fibres and inorganic reinforcements. Coupling agents, such as reactive siloxanes, can transform a composite into a hybrid. Grafting from or to as matrix polymer will form a graft copolymer, that may be considered as a hybrid depending on the nature of the constituents. The aim of this Special Issue of Polymers is to present a selection of research papers and reviews exemplifying self-assembly, hybrid formation and biomimetic principles.

Prof. Em. Dr. Robert A Shanks 
Guest Editor

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