Maria Lluisa Maspoch

On tearing of ductile polymer films using the essential work of fracture (EWF) method

Abstract The essential work of fracture (EWF) technique has been well established and accepted for the fracture characterization of ductile polymer films under in-plane (mode I) loading. In the present study, the technique has been further developed for the characterization of out-of-plane (mode III) tearing fracture of some ductile polymer films including PETG (polyethylene-terephthalate-glycol), PP homopolymer (H0) and a PP copolymer (C1). A two-zone model was proposed to describe the deformation and fracture behaviour of the tearing ligament. In the first zone, which is called zone A and is adjoining the initial crack-tip, the outer plastic zone height increases with the torn ligament length. At the end of zone A, the height of the plastic zone has saturated, and the deformation has entered zone B. The height of the outer plastic zone remains constant with further increase of torn ligament length. The zone B model is applicable to films with a large stabilized plastic zone (such as H0 and C1). It is observed that the tearing specific essential fracture work as measured from the zone A and zone B models are similar confirming the EWF concept can be applied to the mode III out-of-plane tearing of polymer films.

Analysis and Thermo-Mechanical Characterization of Mixed Plastic Wastes

The rejected fraction of plastics from different sorting plants has been studied in terms of composition, processability and enhancement potential. This waste stream consists of a coarse range of plastics families, polyethylene constituting the most abundant one. Blends with two recycled polyethylenes in different proportions were analyzed. The results showed that the mixed fraction was easy to process although it showed a brittle behavior. The addition of recycled polyethylene caused limited ductility improvements, although acceptable levels were achieved in certain mixing ratios. This work demonstrates that mixed plastic wastes can be transformed into a useful material.

Filled PMMA : Mechanical properties and fracture behaviour

The aim of this work is to study the influence of the filler fraction and that of the filler/matrix interfacial adhesion on the mechanical properties and on the fracture behaviour of a poly(methyl methacrylate) PMMA (for injection moulding). The variation of the tensile and flexural mechanical properties with the filler volume fraction was determined. The changes in the fracture behaviour produced by the fillers were studied by evaluating the K IC and G IC parameters of the LEFM (Linear Elastic Fracture Mechanics) by carrying out tests with SENB geometry at room temperature and low strain rates. After fracture surfaces examination by SEM (Scanning Electron Microscopy), it was found that the surface treatment had been rather effective and that the fracture toughening mechanism was multiple crazing.

Polypropylene filled with flame retardant fillers : Mechanical and fracture properties

Two grades of isotactic polypropylene (homopolymer and block copolymer) were filled with magnesium and aluminium hydroxides, and studied focusing the mechanical and fracture characteristics of the composites. As expected, dispersion of such fillers in PP resulted in improved stiffness and reduced tensile yield strength. By one hand, the composites fracture resistance was characterised at low strain rate applying the J-integral concept; the resistance to crack growth initiation (J IC ) was found decreasing as the Mg(OH) 2 concentration was raised in the copolymer PP matrix. By the other hand, the linear-elastic fracture mechanics (LEFM) parameters were determined by means of instrumented impact tests at 1 m/s on the homopolymer PP filled with uncoated Al(OH) 3 particles. The higher the Al(OH) 3 mean particle size, the lower the composite fracture energy (G IC ). In the opposite, with commercial surface-coated filler grades it was not possible to achieve LEFM conditions to characterise the fracture toughness of filled PP at 1 m/s, because the Mg(OH) 2 surface coating, which is applied in practice to improve the melt processing, acts increasing the composite plasticity and reducing the tensile yield strength.