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An anisotropic continuum damage modeling approach was applied to model failure of a composite of unidirectional flax in a polypropylene matrix under quasistatic tensile loading. Tensile, compressive and shear stiffness, and strength values of the composite were characterized according to ASTM standards, and the damage was quantified by optical microscopy. Based on the experimental strength and damage values, an anisotropic strain-dependent material damage model was developed and implemented in the finite element program ABAQUS. This was combined with geometric models of the fabric composites incorporating the yarn geometry. Good agreement was observed between the experimental and numerical stress-strain curves, and the failure strength prediction by the model was within 3.1% of the experimental value. This study shows that combining a geometric model closely incorporating the actual geometry of a fabric composite with an experimentally determined material degradation model can yield good predictions of the mechanical behaviour of the composite. POLYM. COMPOS., 37:2588-2597,

Conductive polymer composites have wide ranging applications, but when they are produced by conventional melt blending, high conductive filler loadings are normally required, hindering their processability and reducing mechanical properties. In this study, two types of polymer-polymer composites were studied: i) microfibrillar composites (MFC) of polypropylene (PP) and 5 wt% carbon nanotube (CNT) loaded poly(butylene terephthalate) (PBT) as reinforcement, and ii) maleic anhydride-grafted polypropylene (PP-g-MA) compatibilizer, loaded with 5 wt% CNTs introduced into an MFC of PP and poly(ethylene terephthalate) (PET) in concentrations of 5 and 10 wt%. For the compatibilized composite type, PP and PET were melt-blended, cold-drawn and pelletized, followed by dry-mixing with PP-g-MA/CNT, re-extrusion at 200°C, and cold-drawing. The drawn blends produced were compression moulded to produce sheets with MFC structure. Using scanning electron microscopy, CNTs coated with PP-g-MA could be observed at the interface between PP matrix and PET microfibrils in the compatibilized blends. The volume resistivities tested by four-point test method were: 2.87•108 and 9.93•107 Ω•cm for the 66.5/28.5/5 and 63/27/10 (by wt%) PP/PET/(PP-g-MA/CNT) blends, corresponding to total CNT loadings (in the composites) of 0.07 vol% (0.24 wt%) and 0.14 vol% (0.46 wt%), respectively. For the non-compatibilized MFC types based on PP/(PBT/CNT) with higher and lower melt flow grades of PP, the resistivities of 70/(95/5) blends were 1.9•106 and 1.5•107 Ω•cm, respectively, corresponding to a total filler loading (in the composite) of 0.44 vol% (1.5 wt%) in both MFCs

Nanofibrillar composites (NFCs) of polypropylene (PP) and poly(butylene terephthalate) (PBT) were produced with PBT as reinforcement. The two polymers were melt-blended, extruded and cold-drawn via necking in order to convert PBT into a nanofibrillar state. The drawn blend was used for manufacture of NFCs via compression moulding. PBT fibrils were isolated by selective dissolution of PP, and used to produce single polymer composites (SPCs), using a one-constituent approach (hot compaction), and a two-constituent approach (film stacking). NFCs and SPCs were subjected to tensile testing to obtain tensile modulus and tensile strength values. Scanning electron microscopy was used to observe PBT fibrils before and after processing of SPCs, having diameters between 100 and 150 nm. For the SPCs, the improvements in tensile modulus (compared to isotropic PBT) were 32% and 36% for the one constituent and two constituent approach, respectively. The corresponding values for tensile strength were 20% and À18%. NFCs of PP/ PBT showed an improvement of 55% in tensile modulus, and 50.24% in tensile strength as compared to isotropic PP.