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Posts sent on: 2015-12-15

15 Dec 2015 
Biodegradable foams created from cassava starch, polyvinyl alcohol (PVA), sugarcane bagasse chitosan and fibers had been obtained by extrusion. The composites were prepared with formulations determined by a constrained ternary mixtures experimental design, employing as variables: starch / PVA, chitosan and fibers from sugars cane. The consequences of varying proportions of the three ingredients on foam real estate were studied, as well the partnership between their properties and foam microstructure. The addition of starch/PVA in increased proportions increased the growth index and mechanical level of resistance of studied foams. Fibers addition improved upon the growth and mechanical homes of the foams. There is a trend of reddish colored and yellow colors when the composites were manufactured with the best proportions of fibers and chitosan, respectively. All the formulations were tolerant to moisture content rise until 75% relative humidity of storage.

In recent years, very much progress has been achieved in the development of biodegradable products using agricultural materials as basis. Various techniques have utilized starch for the creation of different functional elements. Considerable work has been made to develop starch foams as alternative to extended polystyrene for loosefill product packaging software. Starch foams with insulating real estate that are similar to polystyrene foam have been industrially produced by extrusion. Extrusion technology is certainly a high-temperature, short-duration process with the advantage of high versatility and absence of effluents.

Starch foams may be employed to substitute the polystyrene products, but it is known that thermoplastic starch composites own weak mechanical properties, such as for example poor water resistance. Bio-based substances, such as for example cellulose, and other biodegradable polymers are being used as ingredients to improve the dampness sensitivity and mechanical properties of starch-centered foams. Some authors also have reported that the level of resistance of starch foams to the direct connection with water showed an improvement by the addition of a high proportion of polyvinyl liquor. Polyvinyl alcohol is an especially well-suited artificial polymer for the formulation of blends with natural polymers, as it is highly polar and can also be manipulated in water solutions, and depending upon its grade, in useful organic solvents single screw extruder machine as well.

In this work, sugarcane bagasse fiber, an under-utilized waste residue from sugars and alcohol industries was evaluated as filler for starch foams to lessen the moisture sensitivity. Brazil is the largest worldwide producer of ethanol from sugarcane, and huge amounts of fibers is normally still left as a by-product, which is cheap, nontoxic, easily recyclable and its own use plays a part in environmental protection.

Thus, the objectives of the ongoing work were to evaluate the consequences of cassava starch, polyvinyl alcohol, sugarcane bagasse fibers and chitosan about microstructure, density, expansion index, color, drinking water adsorption and mechanical properties of extruded foams using a mixture design methodology.

Cassava starch was provided by Hiraki Market. Sugarcane fiber was supplied by the regional ethanol manufacturers, that was milled and sieved through mesh N-50 finding a product with a size between 290 - 297 μm and before use, it was dried. PVA was purchased from Reagen, chitosan was first obtained from Sigma glycerol and Aldrich from Synth.

A three-aspect constrained simplex mixture design was used to review the consequences of cassava starch/PVA, fibers and chitosan on the real estate of the extruded foams. The assortment selected for every component was based on previous knowledge and ranged from 70 to 100% for starch/PVA, 0 to 2 % for chitosan and 0 to 28% for sugarcane fibers. The starch/PVA employed proportion was 60/40. Table 1 displays the nine employed formulations and two replications at middle point in terms of its original pieces and pseudo-components.

To prepare each formulation, the indicated proportions of starch/PVA, chitosan and sugarcane fibers, glycerol (20 % w/w) and normal water were mixed during 5 min in 780 rpm. The extrusion of the samples was performed in a single-screw extruder with a barrel. Temperature ranges from the feeding to die zone were maintained at 120ºC and two 2.8 mm die nozzles were employed to produce the cylindrical foams extrudates. The screw velocity was maintained at 70 rpm. The extrudates were lower into 100 mm samples with a rotary cutter working at 20 rpm.

Density was calculated because the ratio between your weight and volume. The reported ideals were the averages of ten determinations of each formulation.

The expansion index was measured dividing the extrudates diameter by die orifice size. Reported values were the averages of twenty determinations of every formulation.

SEM analyses were performed with a FEI Quanta 200 microscope. Foams pieces were installed on the bronze stubs utilizing a double-sided tape and then coated with a layer of gold, cross and allowing surface-section visualization. To get the cross-section, the samples were made by immersion into liquid nitrogen in order to avoid the deformation through the fracture. All of the samples were examined applying an accelerating voltage of 20 kV.

Starch foams specimens were pre-dried for 14 days over phosphorous pentoxide and then were placed at 25ºC over saturated salt solutions in separated desiccators having desired drinking water activities. Each foam was weighed at regular intervals specimen, and when two consecutive weights were equal, it was assumed an equilibrium condition was reached. Under the above circumstances, an equilibrium period of seven days was sufficient to establish the dampness equilibrium in all the samples. Equilibrium wetness content material was calculated from the upsurge in the mass of the dried sample after equilibration at confirmed RH. All the testing were executed in triplicate.

A texture analyzer style TA.XT2we with a good 25 N load cell was used to look for the compression power of samples. The 10 mm long extrudates were positioned on a set plate with carefully aligned cut areas in order that the edges were perpendicular to the axis of the sample. After that, each foam was compressed once to 80% of its original size at a loading fee of 5.0 mm/s utilizing a Knife probe. The potent force was reported as compression strength. Reported values had been the averages of fifteen determinations of each formulation.
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