Biodegradable foams based on starch, polyvinyl alcohol, chitosan and sugarcane fibers obtained by extrusion

Biodegradable foams made from cassava starch, polyvinyl alcohol (PVA), sugarcane bagasse fibers and chitosan were obtained by extrusion. The composites were prepared with formulations determined by a constrained ternary mixtures experimental design and style, applying as variables: starch / PVA, fibers and chitosan from glucose cane. The consequences of varying proportions of the three pieces on foam real estate were studied, as well the relationship between their houses and foam microstructure. The addition of starch/PVA in high proportions increased the growth index and mechanical resistance of studied foams. Fibers addition upgraded the growth and mechanical real estate of the foams. There is a trend of reddish colored and yellow colors when the composites were generated with the highest proportions of fibers and chitosan, respectively. All of the formulations were resistant to moisture content increase until 75% relative humidity of storage.

In recent years, very much progress has been achieved in the development of biodegradable products using agricultural material as basis. Various approaches have used starch for the development of different functional substances. Considerable work has been made to develop starch foams as option to expanded polystyrene for loosefill packaging request. Starch foams with insulating homes that are much like polystyrene foam have already been industrially developed by extrusion. Extrusion technology is going to be a high-temperature, short-duration method with the benefit of high versatility and absence of effluents.

Starch foams can be employed to substitute the polystyrene products, but it is known that thermoplastic starch composites contain weak mechanical properties, such as poor water resistance. Bio-based supplies, such as cellulose, and various other biodegradable polymers are being used as ingredients to boost the dampness sensitivity and mechanical houses of starch-centered foams. Some authors have also reported that the level of resistance of starch foams to the immediate contact with water showed an improvement by the addition of a higher proportion of polyvinyl liquor. Polyvinyl alcohol is a particularly well-suited artificial polymer for the formulation of blends with all natural polymers, since it is polar and may also be manipulated in normal water solutions highly, and dependant on its grade, in efficient organic solvents aswell.

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 large amounts of fibers is normally remaining as a by-product, that is cheap, nontoxic, recyclable and its use plays a part in environmental protection easily.

Thus, the objectives of the ongoing work were to judge the consequences of cassava starch, polyvinyl alcohol, sugarcane bagasse fibers and chitosan in microstructure, density, growth index, color, water adsorption and mechanical homes of extruded foams utilizing a mixture design methodology.

Cassava starch was supplied by Hiraki Sector. Sugarcane fiber was supplied by the regional ethanol makers, which 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 acquired from Reagen, chitosan was attained from Sigma Aldrich and glycerol from Synth.

A three-component constrained simplex mixture style was used to review the consequences of cassava starch/PVA, chitosan and fibers on the properties of the extruded foams. The spectrum selected for every twin screw extrusion manufacturer component was predicated on previous encounter 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 used formulations and two replications at middle point in terms of its original parts and pseudo-components.

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

Density was calculated because the ratio between the weight and volume. The reported values had been 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 each formulation.

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

Starch foams specimens were pre-dried for two weeks over phosphorous pentoxide and were placed at 25ºC over saturated salt solutions in separated desiccators having desired water activities. Each foam specimen was weighed at regular intervals, so when two consecutive weights had been equal, it was assumed that an equilibrium state was reached. Under the above circumstances, an equilibrium amount of seven days was sufficient to determine the wetness equilibrium in all the samples. Equilibrium dampness content material was calculated from the increase in the mass of the dried sample after equilibration at a given RH. All the testing were executed in triplicate.

A texture analyzer model TA.XT2i with a 25 N load cell was used to determine the compression durability of samples. The 10 mm long extrudates were positioned on a flat plate with cautiously aligned cut surfaces so that the edges had been perpendicular to the axis of the sample. Then, each foam was compressed once to 80% of its original size at a loading amount of 5.0 mm/s using a Knife probe. The potent force was reported as compression strength. Reported values were the averages of fifteen determinations of each formulation.

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