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Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.

Nanocomposites obtained by casting a mixture of a latex and a n aqueous suspension of cellulose whiskers have been studied. Their mechanical properties (e.g. shear modulus) are found to increase by more than three orders of magnitude in the rubbery state of the polymer matrix, when the whisker content is 6 wt%. This large and unusual effect is discussed on the basis of different types of mechanical models, including semi-phenomenological and numerical finite element calculations. It is concluded that cellulose whiskers form a rigid network linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.

Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex phase. If a water suspension‐mixing procedure is adopted, the fibril breakage that usually occurs during the mixing with a molten polymer can be avoided, and an enhanced filler dispersion can be expected. In this study, different processing methods have been used to prepare composite films, either by film casting (water evaporation) or by freeze drying, followed by classical compression or extrusion processes. The thermomechanical properties of these nanocomposites have been investigated, and the influence of processing conditions and the effect of whisker content have been considered. Processing conditions have a large influence on the mechanical behavior and can be classified in ascending order of their reinforcement efficiency: It can be attributed to a decrease of the apparent whisker aspect ratio, due to gradual breakage and/or orientation of the whiskers when hot pressing or extrusion is used. Below Tg, good agreement is found between experimental moduli and the theoretical predictions of the Halpin‐Kardos equation. On the other hand, above Tg, a spectacular reinforcing effect is observed, which is widely underestimated by this short fiber composite model. This is related to the presence of a rigid cellulose network, linked by hydrogen bonds, when the whisker content is above its percolation threshold. The quality of this network (i.e., density and homogeneity) and thus, the magnitude of the reinforcing effect, depend on processing conditions.

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a b s t r a c tMaterial flow during friction stir welding is very complex and not fully understood. Most of studies in literature used threaded pins since most industrial applications currently use threaded pins. However, initially threaded tools may become unthreaded because of the tool wear when used for high melting point alloys or reinforced aluminium alloys. In this study, FSW experiments were performed using two different pin profiles. Both pins are unthreaded but have or do not have flat faces. The primary goal is to analyse the flow when unthreaded pins are used to weld thin plates. Cross-sections and longitudinal sections of welds were observed with and without the use of material marker (MM) to investigate the material flow. Material flow with unthreaded pin was found to have the same features as material flow using classical threaded pins: material is deposited in the advancing side (AS) in the upper part of the weld and in the retreating side (RS) in the lower part of the weld; a rotating layer appears around the tool. However, the analysis revealed a too low vertical motion towards the bottom of the weld, attributed to the lack of threads. The product of the plunge force and the rotational speed was found to affect the size of the shoulder dominated zone. This effect is reduced using the cylindrical tapered pin with flats.