Structure–property relationships of irradiation grafted nano-inorganic particle filled polypropylene composites

Alumina/polymethylmethacrylate (PMMA) nanocomposites were produced by incorporating alumina nanoparticles, synthesized using the forced gas condensation method, into methylmethacrylate. The particles were dispersed using sonication and the composites were polymerized using free radical polymerization. At an optimum weight percent, the resulting nanocomposites showed, on average, a 600% increase in the strain-to-failure and the appearance of a well-defined yield point when tested in uniaxial tension. Concurrently, the glass transition temperature (T g ) of the nanocomposites dropped by as much as 25°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively. For comparison, composites containing micron size alumina particles were synthesized and displayed neither phenomenon. Solid-state deuterium NMR results showed enhanced chain mobility at room temperature in the nanocomposites and corroborate the observed T g depression indicating considerable main chain motion at temperatures well below those observed in the neat polymer. A hypothesis is presented to relate the thermal and mechanical behavior observed in the composites to the higher chain mobility and T g depression seen in recent ultrathin polymer film research.

Mechanical properties of Al2O3/polymethylmethacrylate nanocomposites

The relationship between nanostructure and properties in polysiloxane layered silicate nanocomposites is presented. Solvent uptake (swelling) in dispersed nanocomposites was dramatically decreased as compared to conventional composites, though intercalated nanocomposites and immiscible hybrids exhibited more conventional behavior. The swelling behavior is correlated to the amount of bound polymer (bound rubber) in the nanocomposites. Thermal analysis of the bound polymer chains showed an increase and broadening of the glass-transition temperature and loss of the crystallization transition. Both modulus and solvent uptake could be related to the amount of bound polymer formed in the system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1595–1604, 2000

Nanostructure and properties of polysiloxane‐layered silicate nanocomposites

Modification of nanoparticles through graft polymerization is able to change the chemical nature of the particles' surfaces and provides an effective means for the preparation of nano-fillers specified for composites manufacturing. The present work focuses on the mechanical role of grafted nano-SiO 2 particles in high density polyethylene composites prepared by melt compounding. The experimental results show that at a content of 0.75 vol%, the modified nano-silica results in a rise in tensile stiffness, tensile strength and impact strength of the composites. The grafted nanoparticles can improve the mechanical performance of the matrix polymer more effectively than the untreated version. In addition, a further enhancement of the composites stiffness and strength can be achieved by crosslinking the concentrated masterbatches, which has not yet been revealed in the authors' previous works on grafted nano-SiO 2 particles/polypropylene composites. It is thus revealed that the introduction of the grafting polymers onto the nanoparticles increases the tailorability of the composites.

Mechanical properties of low nano‐silica filled high density polyethylene composites

A Kaolin-filled, high-density polyethylene (HDPE) system was used to illustrate the influence of particulates on modulus and toughness of the bulk material. A variation of filler content, particulate size and coupling quality for two HDPE-matrix systems with different viscosity led to a strong dependency of elastic modulus and fracture toughness under various testing conditions, e.g. static loading, fatigue and impact. A stiffness improvement with increasing filler content was achieved by all coupling qualities. The developed Kaolin reinforcement of HDPE with optimised coupling offers an improvement of the stiffness and toughness under all investigated loading conditions. The degree of improvement depends on the particulate size and matrix viscosity. The energy dissipation mechanisms were investigated by fractographic analysis.

On Modulus and Fracture Toughness of Rigid Particulate Filled High Density Polyethylene

The reinforcement of rubbers by colloidal filler particles has often been associated with the presence of ‘bound polymer’, that polymer which cannot be removed by solvent extraction from the filled material. This paper demonstrates to the contrary that, for filled polyethylene, bound polymer is observed but reinforcement is not. Indeed, the bound polymer appears to embrittle the filled material. A new model of the filler-polymer interface is proposed to account for these results. It is suggested that there are two interfaces in a filled polymer; one between filler and bound polymer, and a second interface between bound polymer and soluble polymer. This second interface appears to be weak in the case of filled polyethylene and causes failure some 2.8 nm from the true filler surface. The model explains why cross-linking the polyethylene, or increasing its molecular weight, overcomes the embrittlement problem.

Colloidal Reinforcement: The Influence of Bound Polymer

The tear strength of several thermoplastic polymers filled with colloidal silica has been determined as a function of polymer molecular weight. There were two regimes of behaviour. Low molecular weight materials were embrittled by a small amount, around 10% volume fraction, of filler. High molecular weight polymers, on the other hand, were not degraded at low filler concentrations, and some thermoplastics were actually reinforced, that is toughened, by the colloidal particles with a peak in crack resistance at 12% volume fraction. There was found to be a characteristic transition in toughness, similar to that observed with environmental stress cracking, between the low and high molecular weight regimes. It was concluded that a polymer molecular weight above the transition value was a necessary but not sufficient condition for colloidal reinforcement.

Frank R. Sherliker

Papers

Colloidal Reinforcement: The Influence of Bound Polymer

Effect of Polymer Molecular Weight on Colloidal Reinforcement