Starch-based nano-biocomposites

The last decade has seen the development of an alternative chemistry, which intends to reduce the human impact on the environment. The polymers are obviously involved into this tendency and numerous bio-sourced plastics (bioplastics), such as polylactide, plasticized starch, etc., have been elaborated. However, even if a lot of commercial products are now available, their properties (mechanical properties, moisture sensitivity) have to be enhanced to be really competitive with the petroleum-based plastics. One of the most promising answers to overcome these weaknesses is the elaboration of nano-biocomposites, namely the dispersion of nano-sized filler into a biopolymer matrix. This review reports the last developments in nano-biocomposites based on polysaccharides and nanoclays. The main elaboration strategies developed in starch, chitosan, cellulose acetate and pectin based nano-biocomposites elaborated with montmorillonite as the nanofiller are exposed herein. The corresponding dispersion state and properties are discussed.

Progress in nano-biocomposites based on polysaccharides and nanoclays

The overall objective of the present paper is to review the role of V in microalloyed steels with a particular address as to how it affects microstructural evolution and mechanical properties. Its role in thermomechanical controlled processing (TMCP) is emphasised. The review is largely based on work carried out at the Swedish Institute for Metals Research (SIMR) during the last 25 years, but also includes reference to other relevant, published work. A specific aim is to demonstrate the present scientific knowledge of the subject. Therefore the understanding and interpretation of essential phenomena related to microstructure formation and properties are thoroughly examined, ranging from the influence of microalloying on prevention of austenite grain growth and recrystallisation, to precipitation in ferrite and its effect on strength. Within the well-known thermodynamic database, Thermocalc, a special microalloy database has been developed at SIMR, allowing reliable predictions of phase equilibria and thermodynamic functions for phase transformations in microalloyed steels. A comprehensive account is given of the role of V in the most important processing steps that the microalloyed steels are subjected to, viz. TMCP, continuous casting and welding. Compared to the other microalloying elements, Nb and Ti, V exhibits essential differences. In particular, the solubility of its carbonitrides is much larger and the solubility of its nitride is about 2 orders of magnitude smaller than its carbide, contrary to Nb but similar to Ti. For optimal alloy design and thermomechanical processing, proper allowance must be made for these differences. To reach the maximum ferrite grain refinement, ∼4 μm, repeated recrystallisation in a series of rolling reductions is used in TMCP of V-microalloyed steels, so-called Recrystallisation-Controlled-Rolling (RCR), as opposed to traditional controlled rolling of Nb-steels where heavy rolling at low temperatures in the non-recrystallisation regime is the means of attaining grain refinement. RCR presents some important advantages, in particular a more economical hot rolling practice by allowing low reheating and high finishing temperatures. As compared to Nb, V has certain further advantages as a microalloying element due to its greater solubility in austenite. The tendency for hot cracking of cast slabs is much less pronounced and dissolution of coarse V(C,N) compounds is more easily achieved prior to hot rolling than for the corresponding NbC. It is demonstrated that the relatively large solubility of V(C,N) and the much lower solubility of VN than VC makes V an eminent choice for strong and easily controllable precipitation strengthening. A corollary of the difference in VN and VC solubilities is that N becomes an essential microalloying element in V-steels, because it largely determines the density of V(C,N) precipitation and thereby the degree of precipitation strengthening. Moreover, since pure ferrite dissolves more N than C, the total N-content of the steel is normally dissolved in the ferrite before V(C,N) precipitation, whereas only a fraction of the C-content, given by the austenite/ferrite or ferrite/ cementite equilibrium, is dissolved in ferrite. Hence, by precise additions of N, this circumstance facilitates the control of V(C,N) precipitation strengthening.

The rôle of vanadium in microalloyed steels

Preparation and properties of biodegradable starch–clay nanocomposites

Optimization of mechanical properties of thermoplastic starch/clay nanocomposites

Using torsion tests and applying the back extrapolation method, a study has been made of the influence on static recrystallization kinetics of the most common elements (C, Si, Mn, Mo) in low alloy steels and the most common elements (Ti, V, Nb) in microalloyed steels. In the latter case, this influence is studied only at the temperatures at which these elements are in solution, except for Titanium which was partially precipitated in the form of nitrides. Activation energy is the parameter most sensitive to variations in the chemical composition and an expression has been determined to predict its value as a function of the content of each alloying element. Of the different non precipitate-forming alloys sillicon is shown to be the element which most delays recrystallization. Carbon and vanadium in solution have no influence on recrystallization kinetics. It is demonstrated that Nb is the microalloying element which most delays recrystallization.

Influence of Alloying Elements in Solution on Static Recrystallization Kinetics of Hot Deformed Steels

Using torsion tests a model has been constructed to predict the recrystallized fraction of deformed austenite in low alloy and microalloyed steels. The model quantifies the influence of the most common elements (C, Si, Mn, Mo) in low alloy steels and the typical elements (Ti, V, Nb) in microalloyed steels in the recrystallized fraction, when they are in solution. Static recrystallization kinetics follow Avrami's law and expressions for the parameter t0.5 and for the exponent n are not given. The values predicted by the model are compared with the experimental values, good concordance being obtained between both.

Static recrystallization modelling of hot deformed steels containing several alloying elements

Using torsion tests and applying the back extrapolation method a model has been constructed to predict the recrystallized fraction of deformed austenite in Nb, V and Ti microalloyed steels at temperatures below the temperature at which the inhibition of recrystallization commences due to induced precipitation, This temperature, named static recrystallization critical temperature, is modelled as a function of grain size, strain and the solubility temperature. A discussion is made of the importance of being able to predict SRCT in order to effectively apply the model of static recrystallization at temperatures both above and below it. It is demonstrated that Niobium precipitates delay the recrystallization most.

/pdf/static-recrystallization-modelling-of-hot-deformed-2oi8tuxhl9.pdf

Static recrystallization modelling of hot deformed microalloyed steels at temperatures below the critical temperature

Torsion tests were conducted to study the static recrystallization of three microalloyed steels manufactured by electroslag remelting (ESR) with different percentages of vanadium, 0.043%. 0.060% and 0.095%, respectively, and approximately equal percentages of the other alloyforming elements. It was seen that, in contrast to niobium, dissolved vanadium has no influence on the activation energy. The influence only becomes notable when the precipitates start to form and the activation energy increases rapidly, thus inhibiting recrystallization. The critical temperature at which inhibition commences was measured as a function of the vanadium content and the deformation performed, and in all cases it was lower than the dissolution temperature deduced from the solubility products for nitrides, mainly because the testing conditions lacked thermodynamic equilibrium. Finally, a comparison was made of the microstructures obtained in two commercial steels, namely a C-Mn type steel and a vanadium microalloyed steel. Both were subjected to the same cycle of successive deformations, whose temperatures were lower than the critical temperature. After the last deformation, a much harder austenite was obtained in the microalloyed steel than in the C-Mn steel.

Influence of vanadium on the static recrystallization of austenite in microalloyed steels

On the dielectric and ferroelectric properties of Ba 0.75Sr 0.25TiO 3 thin films deposited by RF Sputtering

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