Extrusion Processing of Wheat Gluten Bioplastic: Effect of the Addition of Kraft Lignin

Transcription

1 J Polym Environ (2013) 21: DOI /s ORIGINAL PAPER Extrusion Processing of Wheat Gluten Bioplastic: Effect of the Addition of Kraft Lignin Piya Chantapet Thiranan Kunanopparat Paul Menut Suwit Siriwattanayotin Published online: 18 December 2012 Ó Springer Science+Business Media New York 2012 Abstract Plasticized wheat gluten (WG) was extruded with 0 50 wt% Kraft lignin () contents using a corotating twin screw extruder with circular die. The objective of this study was to evaluate the effect of on the extrusion processing, and on the resulting properties of those new materials. The addition of either 30 or 50 wt% which is a radical scavenger allowed increasing the extrusion die temperature from 80 to 110 C. Moreover, the addition of wt% contents improved the processability of WG in extrusion: it decreased both die pressure and residence time for all studied feed rates and screw speeds. The addition of induced a protein depolymerization and the association between and WG as evidenced by the co-elution of and WG in SE- HPLC. Moreover, the addition of wt% improved mechanical properties and reduced the water absorption of WG-based material. Keywords Bioplastic Extrusion Kraft lignin Free radical scavenger Wheat gluten P. Chantapet S. Siriwattanayotin Department of Food Engineering, Faculty of Engineering, King Mongkut s University of Technology Thonburi, Tungkru, Bangkok 10140, Thailand T. Kunanopparat (&) Pilot Plant Development and Training Institute, King Mongkut s University of Technology Thonburi, Tungkru, Bangkok 10140, Thailand thiranan.kun@kmutt.ac.th P. Menut UMR 1208 Ingénierie des Agropolymères et Technologies Emergentes, INRA, CIRAD, Montpellier SupAgro, Université Montpellier 2, Montpellier, France Introduction Currently, the development of bioplastics from agricultural resources to substitute synthetic polymer has become an important challenge. One of those renewable resources is wheat gluten (WG) which is a low cost co-product from the wheat starch industry widely used for food and/or non-food applications [1]. Nevertheless, a main drawback of proteinbased materials is a narrow processing window on using conventional methods such as extrusion and injection molding [2]. Mostly protein aggregates via sulfhydryldisulfide interchange reactions in the presence of heat and mechanical energy, leading to an increase of protein crosslinking and as a result in a high viscosity. Redl et al. [3] showed that if plasticized WG was extruded with a twin screw extruder, a high screw speed associated with a high specific mechanical energy (SME) led to an important viscous heat dissipation, resulting in an excessive temperature of the product. This consequently generated an excessive cross-linking of the proteins, which inhibited elastic recovery for large deformation, resulting in an extrudate irregular aspect due to the multiplication of the network rupture under shear. The best extrudates of plasticized WG were thus obtained from low temperature (60 C) and low SME input, which restrict the possibilities for manufacturers to tailor the final product properties through the control of the cross-linking density. Both radical and nucleophilic reaction pathways are involved in protein aggregation as shown in Fig. 1 [4]. Shear is postulated to be the starting point of free radical formation (thiyls), and the overall cross-linking process is sensitive to temperature. Consequently, it should be possible to increase the upper processing temperature limit by limiting or delaying the disulfide reactions using radical scavenger [5].

2 J Polym Environ (2013) 21: Fig. 1 General mechanism of gluten aggregation. A detailed description of the different mechanisms involved is given in reference [4] To enlarge the processing window of protein, a number of researches proposed the use of chemical additives [6] such as sodium sulfite as a reducing agent [7 9], or salicylic acid as a radical scavenger [5, 10] to decrease protein aggregation and blend viscosity during extrusion or injection molding. Sodium sulfite was also used to improve the flow properties of plasticized sun flower protein for the injection molding: the obtained network being less reticulated due to the additive [9]. Ullsten et al. [5, 10] showed that salicylic acid, which is a radical scavenger, allowed an enlargement of the extrusion window for the WG by delaying protein aggregation. However, the mechanical properties of WG film containing 1 wt% salicylic acid were not improved due to a lower degree of protein aggregation, although the WG extrudate containing 1 wt% salicylic acid was exposed to higher processing temperature than the WG extrudate without salicylic acid [5]. In this study, an alternative way based on the use of Kraft lignin (), which is a by-product of the alkaline pulping process known as a radical scavenger, was proposed. Hence, may delay the disulfide reactions by hydrogen donation for thiyl radicals, resulting in a reduction of viscosity and an enlargement of extrusion window. Our previous studies [11, 12] showed that the addition of on WG materials decreased the viscosity of the blend during mixing due to protein depolymerisation [12]. In addition, association of with WG was evidenced by the co-elution of and WG in size exclusion high-performance liquid chromatography (SE-HPLC) coupled with fluorescence and UV detectors [11]. In terms of physical properties, the addition of improved mechanical properties and water absorption of WG-based materials after mixing and thermomolding [12]. However, the effect of on the processability and properties of WG-based materials prepared by extrusion has not been investigated, while this information is important in view of biomaterial production. The aim of this research study was thus to evaluate the possibility to enlarge the extrusion window of WG materials by using as a free radical scavenger. Firstly, the effect of on processability of WG extrusion was investigated via the measurement of processing parameters such as the residence time, the die pressure or the extrudate swelling. Secondly, to study the effect of those changes on the material internal structure, protein aggregation was characterized by SE-HPLC. Finally, the physical properties of the materials were determined in terms of mechanical properties and water absorption. Experimental Section Materials Commercial vital WG powder was obtained from Winner group enterprise Ltd. (NWS, Australia). Its protein content was 76.1 % (dry basis), moisture content was 8.2 % according to the manufacturer. powder was obtained from Raja engineering Co. Ltd. (Bangkok, Thailand). Its lignin content was 97 % (dry basis), moisture content was 5 % according to the manufacturer. AR Grade anhydrous glycerol was used (Ajax Finechem Ltd, Auckland, New Zealand). Sample Preparation for Extrusion WG and powder were mixed with glycerol by using a food mixer (King mixer, Model K-05, USA) at low speed for 10 min and medium speed for 1 min. Addition of glycerol as a plasticizer is necessary in order to extrude WG. Plasticizers decrease the glass transition temperature (T g ) of the mixture. In this study, the glycerol concentration was fixed at 30 wt% which was a concentration sufficient to decrease significantly the T g without problems of miscibility with WG and [12]. To allow direct comparison between samples, this glycerol concentration was constant in every sample. Then, the mixture was pelletized into particles with diameters of 8 10 mm. The composition of different WG: ratio was shown in Table 1. Extrusion Process The extrusion was performed with a co-rotating, self-wiping twin screw extruder (model LTE-20-40, Labtech

3 866 J Polym Environ (2013) 21: Table 1 Composition of WG-based materials containing different contents Composition [%wt] Sample 0 % 10 % 30 % 50 % WG Glycerol Engineering Co., Ltd., Thailand), equipped with a circular die with a diameter of 3 mm. The extruder consisted of 10 heating zones, divided into 8 heating zones of barrel and 2 heating zones of die head. The total length of the screw was 800 mm, diameter of screw was 20 mm. Figure 2 showed a schematic of the screw configuration [13]. The experimental design was based on the investigation of the influence of feed rate (1, 1.5 and 2 kg/h) and screw speed (50, 100 and 150 rpm) at a constant extrusion temperature (barrel temperature increased about 5 10 C in each heating zone to obtain a final die temperature at 80 C) and the influence of extrusion temperature (barrel temperature increased about 5 10 C in each heating zone to obtain a final die temperature ranging from 60 to 120 C) at a constant feed rate (1.5 kg/h) and screw speed (50 rpm). Mean residence time of extrudate was determined by introducing 0.5 g of colored feed (violet for 0 % and white for 10, 30 and 50 % ) and estimated by visual evaluation of color change at the die opening [3]. Using this method, we are able to estimate the residence time with a precision of about 5 10 s depending on extrusion conditions. The energy consumption of the extruder motor was followed by the measure of the electrical consumption intensity, expressed in Ampere (A). The extrudate diameter was measured with a vernier caliper to calculate extrudate swelling according to Eq. (1) [3]. Extrudate swelling ¼ d=d 0 ð1þ where d is extrudate diameter and d 0 is die diameter (d 0 = 3 mm). SE-HPLC Changes in the molecular size distribution of the WG proteins were characterized SE-HPLC. Exhaustive presentation of the method is given in Redl et al. [14]. Briefly, samples were ground in presence of liquid nitrogen using a laboratory ball mill (Retsch, Model S100, Germany), and then blended with soluble wheat starch (1/5 g/g) which allows the glycerol absorption. The obtained powder (160 mg) was stirred for 80 min at 60 C in the presence of 20 ml of 0.1 M sodium phosphate buffer (ph 6.9) containing 1 % sodium dodecyl sulfate (SDS). The SDS-soluble protein extract was recovered by centrifugation (30 min at 39,0009g and 20 C) and 20 ll were submitted to SE-HPLC fractionation (first extract). The pellet was suspended in 5 ml SDS-phosphate buffer containing 20 mm dithioerythritol (DTE). After shaking for 60 min at 60 C, the extract was sonicated (Vibra Cell 20 khz, Bioblock scientific) 3 min at 30 % power setting. Disulfide and weak bonds are disrupted by those chemicals, whose efficiencies are further increased due to ultrasonic waves. As a result, these treatments bring insoluble protein from the pellet into solution. After centrifugation (30 min, 39,0009g,20 C), a part of the supernatant was then mixed volume to volume with SDS-phosphate buffer containing 40 mm iodoacetamide in order to alkylate thiol groups. The reaction was carried out for 1 h in darkness, at room temperature. 20 ll of this solution was submitted to SE-HPLC fractionation (second extract). Fig. 2 Screw configuration (L/D ratio = 40) [13]

4 J Polym Environ (2013) 21: The SE-HPLC apparatus is a Waters model (Alliance). A TSK G4000-SWXL (Tosoh Biosep) size exclusion analytical column ( mm) was used with a TSK- SW (Tosoh Biosep) guard column ( mm). The columns were eluted at ambient temperature with 0.1 M sodium phosphate buffer (ph 6.9) containing 0.1 % SDS. The flow rate was 0.7 ml/min, and proteins were recorded at 214 nm for UV measurement. For the fluorescence measurement, the excitation wavelength was 330 nm and was recorded on emission wavelength of 400 nm. The eluted molecules were detected by fluorescence about 10 s after the UV measurement. Therefore, the elution times were corrected for the comparison between the fluorescence and UV absorbance chromatograms. Mechanical Properties Twenty-five grams of extrudates were molded at 100 C for 15 min in a Hydraulic Press Machine (20 T., SMC TOYO METAL Co., Ltd., Thailand). A load of 1 ton was directly applied to the sample in the mold. The thickness of samples was approximately 2 mm. The extrudate sheet was cut into a dumbbell shape of 75 mm overall length and 4 mm width for the elongating part and preconditioned at 25 C, 53 % RH over a magnesium nitrate salt (Mg(NO 3 ) 2 ). Tensile tests were performed on a Texture Analyzer (Stable Micro System, TA-XT. plus, Surrey, UK). The initial grip separation was 50 mm and crosshead speed was 1 mm/s [15]. Each sample was analyzed in 4 replications. Water Absorption The thermo-molded samples prepared for the mechanical properties test were also cut into a disc with a diameter of 24 mm to determine water absorption of materials [16]. Then, they were dried at 0 % RH over a phosphorus pentoxide salt (P 2 O 5 ) until their weight was constant (W i ). Then, they were immersed in 50 ml distilled water containing 0.05 % sodium azide (NaN 3 ) to avoid the microbial growth at 25 C. The swollen samples were wiped and weighed (W w ) after 1 week. Then, they were dried 0 % RH over a P 2 O 5 salt until their weight was constant (W f ). Each sample was analyzed in 4 replications. Water absorption was calculated by the Eq. (2). Water absorption ð% Statistical Analysis Þ ¼ 100 W w W f = Wi ð Þ ð2þ The experimental data presented in this study was mean values with standard deviations. The statistical program Minitab (version 16) was used to perform all statistical calculations. The one-way ANOVA and least significant difference (LSD) test were used to compare means at 95 % confidence (p \ 0.05). Table 2 Operating conditions and measured value of 0 % sample extruded at 1.5 kg/h of feed rate and 50 rpm of screw speed Sample Operating condition Motor Current Setting temperature [ C] [A] Barrel zone Die zone 9 10 Measurement Die pressure [bar] Residence time [s] Extrudate swell Appearence 1cm 0 % [80 n/a n/a Disrupted

5 868 J Polym Environ (2013) 21: Table 3 Extrusion conditions and measured value of 0, 10 and 30 % samples Sample Operating condition Motor Setting temperature [ C] Current [A] Barrel zone Die Zone 9 10 Screwspeed [rpm] Feed rate [kg/hr] Measurement Die pressure [bar] Residence time [s] Extrudate swelling Appearence 1cm 0% % % Results and Discussion Effect of on Processability of WG Extrusion In order to find the optimum extrusion temperature to extrude plasticized WG (0 % sample), the extrusion temperatures were varied at 60, 80, 90, 110 and 120 C of die temperature (barrel temperature increased about 5 10 C in each heating zone to obtain the setting die temperature) at constant screw speed (50 rpm) and feed rate (1.5 kg/h) as shown in Table 2. At a die temperature of 60 C, the pressure in the extruder was so high that it

6 J Polym Environ (2013) 21: exceeded its limitation ([80 bar), and processing was not possible. At this temperature, the viscosity of the sample was too high, and the molten state required for extrusion was not obtained [3]. At 80 C of die temperature, the most smooth extrudate surface was obtained. At higher die temperatures (90 and 100 C), the extrudates started to exhibit an irregular shape, and they completely ruptured at a die temperature of 120 C which was attributed to an excessive aggregation [17]. Therefore, a die temperature of 80 C was chosen to study the effect of process parameters and contents on WG extrusion. While processing plasticized WG materials without (0 %), increasing the feed rate at a constant screw speed resulted in an increase of die pressure and motor power consumption (Table 3, first part), which was due to the higher degree of filling in the extruder barrel [18]. This higher degree of filling favored a more efficient transport of mass in the extruder, and therefore also reduced the residence time. Increasing the screw speed resulted in a decrease in die pressure and residence time, a phenomenon amplified by the lower blend viscosity at high shear rate, due to plasticized protein blend being a non-newtonian fluid [15]. In addition, increasing screw speed decreased the extrudate swelling which was associated with the elastic recovery of extrudate [19]. The effect of addition on process parameters of WG extrusion was also shown in Table 3. All the samples presented here were prepared with the same amount of glycerol, therefore the observed evolution was only associated to the effect of. Comparing with the same condition of WG extrusion, the addition of decreased significantly the die pressure, the motor current and the residence time. This can be explained by the fact that the addition of into plasticized WG decreased the blend viscosity at processing temperature, as we already observed in a previous study in different processing conditions [12]. Therefore, this suggested that addition significantly reduced the SME needed to extrude the material, which was indicated by the combination of a lower residence time and a lower power consumption of the extruder [20]. This constituted a key element for an industrial processing of environmentally friendly materials. Additionally, in the presence of, extrusion can be operated at higher temperature without the appearance of rupture in the extrudate as shown in Table 4. The maximum processing temperature in Table 4 corresponded to condition that we were able to reach without degrading the extrudate appearance. As an example, we illustrated the case of 30 %, for which different extrusion conditions were reported. It can be observed that if for die temperatures of 100 and 110 C, a smooth extrudate was obtained, it was not the case at 120 C, for which the extrudate appearance was very irregular. In that case, it was considered that the maximum temperature at which the product can be extruded was 110 C, and the same approach for the other samples was conducted, beside the data relative to this maximum temperature conditions was only presented in Table 4. Comparing the effect of content on WG extrusion, the addition of allowed increasing the extrusion die temperature from 80 to 100 C for 10 % and 110 C for 30 and 50 %. In addition, it also improved the material processability by decreasing die pressure and residence time. addition decreased the extrudate swelling and improved its appearance especially at 30 % (Table 4). The processability improvement of on WG extrusion can probably be explained by the low rubbery modulus of /WG blends at those temperatures as already observed in our previous study [12]. This result supported the idea that can be used as an effective additive to facilitate the WG extrusion. Effect of on Protein Aggregation Changes in protein aggregation of 0 30 % extrudates extruded at 80 C of die temperature were investigated by SE-HPLC. Figure 3a (SDS-soluble) and b (SDS-insoluble) presented the elution profiles of native WG and powder as received. elution profile is essentially characterized by a single peak at 19 min, while WG protein showed a large range of size, with elution time ranging from 8 to 26 min. The elution profile of /WG mixture prepared by simple mixing was a simple combination of the elution profile of WG and powder (data not shown), which confirmed that their extinction coefficient were not modified by simple blending as already shown in our previous study [11]. The effect of the content on protein solubility was shown in Figs. 3c (SDS-soluble) and d (SDS-insoluble), for a single die temperature of 80 C. The peak position was not modified when compared to Fig. 3a and c, suggesting that a large quantity of remains free and was not modified after extrusion with WG. However, it can be noticed an increase of Fraction 1 to Fraction 4 (F1 F4) areas with increasing content, while Fig. 3d showed a clear decrease of the insoluble fraction. The protein solubility was also characterized for materials prepared at their maximum processing temperature depending on their content. Figure 3e (SDS-soluble) and f (SDS-insoluble) presented the elution profiles of extrudates with 0, 10 and 30 % contents extruded respectively at 80, 100 and 110 C of die temperature. SDS-soluble extracts of these extrudates (Fig. 3e) presented the same trend as the one previously observed when only the content was changed (Fig. 3c). In contrast,

7 870 J Polym Environ (2013) 21: Table 4 Maximum extrusion conditions and measured value of 10, 30 and 50 samples at 1.5 kg/h of feed rate and 50 rpm of screw speed Sample Operating condition Measurement Setting temperature [ C] Barrel zone Die zone 9 10 Motor Current [A] Die pressure [bar] Residence time [s] Extrudate swelling Appearence 1cm 0 % % 30 % Irregular 50 % Fig. 3f showed an increase of the insoluble fraction when both content and die temperature increased, which was associated with a change in the protein distribution, characterized by a larger number of high-molecular weight proteins. As described in the literature and observed on various WG-based materials, such as composites [21], high thermal treatment induced high levels of protein aggregation through disulfide bridges, leading to an increase in the protein molecular weight. This study showed that this behaviour was not impaired by addition, beside its depolymerizing effect as previously described. The quantity of soluble and insoluble protein in each material was calculated from the chromatograms after subtraction of the contribution in each sample, on the basis of its initial content in the material. Table 5 summarized the percentage of protein content in SDSsoluble and SDS-insoluble fractions, for extrudates extruded at 80 C and at the maximum die temperature possible. As expected, processing plasticized WG (0 % materials) at 80 C of die temperature results in a significant decrease of the protein solubility in SDS, if compared to native WG powder. This was a clear indication of WG protein cross-linking during extrusion. The addition of up to 30 % clearly went against this cross-linking, as the soluble fraction increase, while the insoluble one decreased to values similar as the ones found in native WG. The higher the concentration, the higher the protein depolymerization. This can be attributed to the radical scavenging properties of, which allowed the capture of thiyl radicals formed during processing, and therefore prevented the processes through which they could finally induce the formation of new disulfide bond in between proteins. In addition, as previously reported [11], the addition of on WG can modify the absorbance of the soluble compounds due to association with WG, which explained why the total amount of protein measured with this method exceed 100 % at high content. This imposed some precaution in the analysis of our results. However, the observed tendencies in protein solubility change were so significant that they can be considered as good indications of the general trends. From those first results, it was clear that the addition of at 80 C of die temperature resulted in both a /WG association and a WG depolymerisation [11], which can explained the change in die pressure and swelling observed in the previous part. The extrusion of /WG material at the maximum die temperature possible showed some interesting tendencies. In that case, the addition of, which acted as depolymerizing agent, was compensate by an increase in temperature, which favoured cross-linking. The result was that we obtained products with high content but also high cross-linking levels, especially at 110 C, when 30 % was used. In that case, about 40 % of the proteins became

8 J Polym Environ (2013) 21: Fig. 3 UV-size exclusion distribution profiles of SDS-soluble (a, c, e) and SDS-insoluble (b, d, f) protein fractions of WG, powder and 0, 10 and 30 % extrudates respectively extruded at different die temperature, 50 rpm, and 1.5 kg/h insoluble, which was a level significantly higher than the one obtained by processing WG without. Additionally, mass distribution profiles shown in Fig. 3f shown that those proteins were associated in very large clusters. Therefore, an increase in extrusion temperature with content led to a high protein cross-linking. As a result of this section, it appeared that the addition of induced a protein depolymerization because can capture the thiyl radicals formed under shear and thermal treatment occurring during extrusion. The protein depolymerization increased with content, but this effect can be overcome by the flexibility due to the addition on the extrusion temperature, which can be increased to values significantly higher than during plasticized WG extrusion. This allowed obtaining materials with both high content and high levels of protein cross-linking. /WG Association Due to the fluorescence properties of, its association with WG can be detected during their co-elution in SE- HPLC using a fluorescence detector. Our previous study showed that mixing and compression molding promoted a strong association of with WG [11]. As was freely eluted with and after Fraction 5 (Fig. 3a), the /WG association during extrusion can be investigated in WG F1 F4, where any fluorescence measurement was link to the presence of associated with high molecular weight proteins. The ratio between the fluorescence and UV area of extrudate for WG soluble and insoluble fraction was calculated and were presented in Table 6. Fluorescence area was only related to concentration, while UV area was related to WG

9 872 J Polym Environ (2013) 21: Table 5 Protein content (%) in SDS-soluble and SDS-insoluble fractions of native WG, andextrudates extrudedat different die temperature, at 50 rpm, and 1.5 kg/h Sample Protein Area/Total theory protein area [%] Soluble (F1-F6) Insoluble (F1-F5) Total Native WG Extrudate at 80 C 0 % % % Extrudate at maximum die temperature 0 % (80 C) % (100 C) % (110 C) Table 6 Ratio between fluorescence area and UV area of soluble and insoluble fractions of % samples extruded at different die temperature, at 50 rpm, and 1.5 kg/h Sample (die temperature) Fluorescence area/(uv area) Soluble fraction F1 F2 F3 F4 Insoluble fraction Extrudateat 80 C 10 % (80 C) % (80 C) Extrudate at maximum die temperature 10 % (100 C) % (110 C) Table 7 Mechanical properties and water absorption of 0 30 % materials prepared by molding at 100 C Sample (die temperature) 0% (80 C) 10 % (80 C) 30 % (80 C) 10 % (100 C) 30 % (110 C) Mechanical properties Young s modulus [MPa] Tensile strength [MPa] Elongation at break [%] Water absorption [%] 4 ± 2 c 1.1 ± 0.2 b 109 ± 21 a 90.7 ± 3.0 a 11 ± 1 cd 1.4 ± 0.2 b 66 ± 39 a 81.6 ± 3.4 b 107 ± 6 a 2.8 ± 0.3 a 3 ± 0.2 b 69.0 ± 2.9 c 14 ± 2 b 1.6 ± 0.5 b 70 ± 48 a 79.8 ± 3.4 b 92 ± 7 a 2.6 ± 0.5 a 3 ± 1 b 65.6 ± 2.5 c Values with different superscript letters in the same column are significant difference (p \ 0.05). Significance of the differences was tested with ANOVA LSD test concentration. /WG association appeared to be more important on high molecular weight glutenin polymers (F1), then c, b and a-gliadins (F3 and F4) and F2 for both 10 and 30 % contents. Apparently, was not randomly associated on the WG, but specifically on the high molecular weight of WG. The association appeared to be more pronounced when content and extrusion temperature increased, which suggested a link between the gluten depolymerisation and the /WG association, both being more pronounced when higher temperature processing temperature was used. Effect of on Physical Properties of WG-Based Materials Mechanical properties and water absorption of 0 30 % materials prepared by compression molding the extrudate at 100 C were shown in Table 7. In terms of mechanical properties, the tensile strength and Young s modulus of materials drastically increased when content increased, but the elongation at break decreased. The addition of decreased the water absorption of the WG/ materials due to the hydrophobic properties of. When the die temperature increased to its maximum for each concentration, only little (at 10 %) or no (at 30 % ) effect of die temperature on mechanical properties and water absorption of materials were observed. It has indeed to be taken into account the fact that not only the die temperature, but also the residence time in the extruder were different. Additionally, all samples were similarly exposed to temperatures at 100 C during compression molding, leading to protein aggregation. Conclusion In this study, the production of new biodegradable materials by extrusion was investigated. Because WG basedmaterials properties were tightly related to the cross-linking extent in the product, it is important to offer a large range of processing conditions allowing different levels of reticulation in the product. Additional requirements for bioplastic production are the conception of process with reduced energetic consumption, in order to guarantee a low environmental impact of the product production. In this study, the extrusion of plasticized WG with various amount of was investigated, mapping different processing conditions in terms of temperature, feeding rate and screw speed. The addition of to WG effectively allowed increasing the range of processing temperature, giving more opportunities to control material properties. Moreover, the addition of % contents improved the processability of WG by decreasing both die pressure and

10 J Polym Environ (2013) 21: residence time for all studied feed rates and screw speeds. This may be explained by the free radical scavenging properties of, leading to a protein depolymerization evidenced by a decrease of the insoluble protein content. However, when the extrusion temperature increased, the insoluble protein content increased. /WG association appeared to be dominant for high molecular weight polymers (F1). The addition and an increase of extrusion temperature increased Young s modulus and tensile strength, decreased elongation at break and reduced water absorption of /WG materials. In this study, it can be concluded that is an efficient additive to enlarge the WG extrusion window. not only improved the processability including die pressure, residence time and extrudate swelling of WG, but also improved mechanical properties and water resistance of WG materials. Acknowledgments The authors are very grateful to King Mongkut s University of Technology Thonburi for supporting SE-HPLC column in this research. References 1. Day L, Augustin MA, Batey IL, Wrigley CW (2006) Trends Food Sci Tech 17:82 2. Verbeek CJR, van den Berg LE (2009) Macromol Mater Eng 10: Redl A, Morel M-H, Bonicel J, Vergnes B, Guilbert S (1999) Cereal Chem 76: Auvergne R, Morel M-H, Menut P, Giani O, Guilbert S, Robin J J (2008) Biomacromolecules 9: Ullsten NH, Gallstedt M, Johansson E, Graslund A, Hedenqvist MS (2006) Biomacromolecules 7: Verbeek CJR, van den Berg LE (2009) Recent Pat Mater Sci 2: Jane J-L, Wang S (1996) (Ames, IA) US 5,523, Ralston B, Osswald T (2008) J Polym Environ 16: Orliac O, Silvestre F, Rouilly A, Rigal L (2003) Ind Eng Chem Res 42: Ullsten NH, Cho S-W, Spencer G, Gallstedt M, Johansson E, Hedenqvist MS (2009) Biomacromolecules 10: Kunanopparat T, Menut P, Morel M-H, Guilbert S (2009) J Agric Food Chem 57: Kunanopparat T, Menut P, Morel M-H, Guilbert S (2012) J Appl Polym Sci 125: Labtech Engineering Co., Ltd., Instruction manual for scientific twin screw extruder types LTE and LTE (2008) Redl A, Morel M-H, Bonicel J, Guilbert S, Vergnes B (1999) Rheol Acta 38: Sakunkittiyut Y, Kunanopparat T, Menut P, Siriwattanayotin S J Appl Polym Sci doi: /app Muensri P, Kunanopparat T, Menut P, Siriwattanayotin S (2011) Compos A 42: Morel M-H, Redl A, Guilbert S (2002) Biomacromolecules 3: Akdogan H (1996) Food Res Int 29: Liang J-Z (2004) Polym Testing 23: Janssen LPBM, Mościcki L, Mitrus M (2002) Int Agrophys 16: Kunanopparat T, Menut P, Morel M-H, Guilbert S (2008) Compos A 39:1787