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Extruded cylindrical strands: mechanical properties correlated with the formation of biodegradable films through blown extrusion.
Abstract:
The objective of this study was to determine the mechanical and viscoelastic properties of extruded cylindrical strands from biodegradable polymer blends and to verify the correlation of the blend properties with their capacity to form films in the blown extrusion process. The production of biodegradable films would only occur if the extruded strands showed adequate characteristics. The strands were produced by extrusion with blends containing starch, glycerol, and fatty acids (caproic, lauric, and stearic). These blends were compared with a standard formulation containing poly (butylene adipate-co-terephthalate) (PBAT), a biodegradable polymer. From the mechanical tension tests, the extruded strands containing fatty acids differed significantly from the standard one, it was not clear the possibility to establish a comparison between the mechanical properties of the extruded strands and the formation of films. The rheological tests indicated that the polymer blends presented the desired viscoelastic characteristics for the film formation by blown extrusion. POLYM. ENG. SCI., 52:35-41, 2012. [c] 2011 Society of Plastics Engineers

Article Type:
Report
Subject:
Extrusion process (Research)
Microbial mats (Mechanical properties)
Microbial mats (Chemical properties)
Microbial mats (Production processes)
Authors:
Nobrega, Marcelo Medre
Bona, Evandro
Muller, Carmen Maria Olivera
Yamashita, Fabio
Pub Date:
01/01/2012
Publication:
Name: Polymer Engineering and Science Publisher: Society of Plastics Engineers, Inc. Audience: Academic Format: Magazine/Journal Subject: Engineering and manufacturing industries; Science and technology Copyright: COPYRIGHT 2012 Society of Plastics Engineers, Inc. ISSN: 0032-3888
Issue:
Date: Jan, 2012 Source Volume: 52 Source Issue: 1
Topic:
Event Code: 320 Manufacturing processes; 310 Science & research
Geographic:
Geographic Scope: Brazil Geographic Code: 3BRAZ Brazil
Accession Number:
277001077
Full Text:
INTRODUCTION

There is an industrial interest in biodegradable films, especially for packaging. Starch is an abundant and low-cost polymer that comes from renewable resources, and over the last three decades, starch has been studied as a component in films and plastics (1-4).

The majority of studies on biodegradable films are focused on casting method (5-10), but the blown extrusion is a more cost effective processing method, since it is faster, requires less space, and demands a smaller number of production stages compared with casting. Extrusion is also the method utilized in large-scale production of commercial films. However, the production of extruded films with only starch is not viable, since starches have low mechanical resistance and high water vapor permeability (WVP). As such, starches do not have suitable characteristics for commercial production and applications (3), (11-13). One solution to this problem would be to work with blends of starch and biodegradable polymers such as poly (butylene adipate-co-terephthalate) (PBAT), which has mechanical characteristics similar to the characteristics of conventional polymers such as polyethylene and polypropylene (11), (14), (15). Fatty acids can also be incorporated to decrease WVP (16).

For film formation through blown film extrusion, it was necessary to have a blend that supported both the longitudinal tension exerted by the spooler as well as the force exerted by the injected air, which expands the matrix in the transversal direction. If the polymer blend does not possess adequate viscoelastic properties during the extrusion process, no film will form. For production of films by extrusion using polymer blends, the components of the blend were first extruded in an initial step for the production of cylindrical strands, after which the strands were cut to form pellets (see Fig. 1).

[FIGURE 1 OMITTED]

The objective of this study was to determine the mechanical and viscoelastic properties of extruded cylinder strands composed of polymer blends and to verify the correlation between the properties of the blends and film formation through blown extrusion. Therefore, the development of biodegradable films from polymer blends would be accelerated, since only films with adequate characteristics in the extruded strands would form. The polymer blends were produced by extrusion and contained starch, glycerol, fatty acids (caproic, lauric, and stearic), and PBAT.

MATERIALS AND METHODS

Material

Starch from cassava (Manihot esculenta) was provided by Indemil (Diadema SP, Brazil) under the brand name AmidoMani. The biodegradable polymer PBAT was provided by BASF under the commercial name Ecoflex [R]-F. Commercial glycerol (Dinamica, Brazil) was utilized as a plasticizer, and the fatty acids that were used were caproic acid (99%, Vetec, Brazil), lauric acid (98%, Vetec, Brazil), and stearic acid (PA, Synth, Brazil).

Production of the Extruded Strands Composed of Starch, Glycerol, Fatty Acids, and Films

The extruded cylinders were produced in a BGM brand mono-screw pilot extruder (model EL-25, Brazil) equipped with a screw measuring 250 mm in diameter. The screw velocity was 35 rpm with a temperature of 120 [degrees] C in the three cannon zones and at the pellet forming matrix. The formulations for the extruded material are shown in Table 1.

The fatty acid was mixed with glycerol with a mixer for approximately 1 min. These glycerol + fatty acid mixtures were incorporated with the starch, and the blend was extruded to produce cylinders composed of thermoplastic starch (TPS) and fatty acids.

The films were produced by blow extrusion using a pilot extruder BGM (model EL-25, Brazil) with a blowing system made up of a 250-mm diameter screw, four heating zones, and an external cooling air ring with a 300-350-mm diameter for film formation. The screw speed was maintained at 35 rpm, and the temperature was kept at 120[degrees] C.

Diameter

The diameter of the extruded cylinders was determined using a digital caliper (Mitutoyo, Brazil) with a resolution of 0.001 mm.

Mechanical Tension Tests

Tension tests of the strands were performed in a texturometer (Stable Micro Systems, model TA TX2i, England) in accordance with a modified method from the American Society for Testing and Materials (ASTM D-882-00, 2001). The specimens that were 60 mm in length were adjusted to the grips of the equipment, which had an initial distance of 30 mm and a velocity of 0.8 mm/s. The properties determined in the tension tests were maximum tensile resistance (MPa), alignment at rupture (%), and Young's modulus (MPa).

A total of 10 tests were conducted for each formulation. Prior to testing, the samples were conditioned under 53% relative humidity (RH) for 48 h.

Mechanical Shear Force Tests

The shear force tests of the strands were performed using a texturometer (Stable Micro Systems, model TA TX2i, England) with the probe HDP/BSK BLADE SET WITH KNIFE. The pre-test, test and post-test velocity was 5 mm/s and the trigger force was 0.05 N. The shear force resistance (F) was determined for samples measuring 30 mm in length.

A total of 10 tests were conducted for each formulation. Prior to testing, the samples were conditioned under 53% RH for 48 h.

Mechanical Relaxation Tests

Relaxation tests on the cylinders were conducted using a texturometer (Stable Micro Systems, model TA TX2i, England) in accordance with a method provided by the ASTM D-882-91, 1996. The samples (130 mm in length) were adjusted to the grips of the equipment, which had initial distance of 100 mm and a velocity of 0.8 mm/s until 1% of the rupture elongation was reached (which was determined previously in the tension tests), and the decrease of the force was measured at 0.04-s intervals for 1 min. Adjustments to the relaxation data were calculated in accordance with Eq. 1.

%relaxation = [- (F (60s)/[F.sup.0])] x 100

The relaxation data were normalized and analyzed with an empirical model proposed by Peleg (17), in which the force (F) was normalized through a parameter of decline F(t) as shown in Eq. 2 (8).

F(t)/ [F.sup.0] =1 - [C.sup.1] * t/[C.sup.2] + t

Parameters [C.sup.1] and [C.sup.2]of Eq. 2 were calculated by non-linear regression using STATISTIC A 5.0 software (Statsoft, 1995).

Analysis of the Data

From the tension, shear, and relaxation tests, parameters were obtained to compare samples from different blends. The differences between sample properties were determined by an analysis of variance (ANOVA) and Tukey tests with 5% significance. The tests were conducted in STATISTICA 5.0 software (Statsoft, 1995).

RESULTS AND DISCUSSION

The PPBAT formulation containing 50% PBAT in its composition (Table 1), along with starch and glycerol, was used as a standard to compare to the other formulations, since this formulation was studied by Costa (13) and presented a good capacity for producing high quality film via blown extrusion.

In a subjective evaluation, the extruded cylinder strands contained 12.8% glycerol (C128, [C.sub.a] l28, [L.sub.a]l28, and E128), which was rigid and fragile, likely due to the low concentration of glycerol and did not permit adequate plasticization. The strands containing fatty acids ([C.sub.a], [L.sub.a], and E) presented a lower rigidity than the control (C), but the strands were still quite rigid. Therefore, these strands could not be analyzed in terms of maximum mechanical force or tested with relaxation tests.

Considering that the incorporation of PBAT increases the mechanical properties of the film, an amount of 30% of PBAT was added to the formulation to verify if the extruded strand properties were correlated with the film formation by blown extrusion. A subjective evaluation of the films was performed to verify the homogeneity, handling, and tendency to tear, and the results are presented in Table 2.

After the analysis of the extruded strands, PBAT were incorporate to the formulations. All the formulations were film forming, but that ones with stearic acid presented the poorest subjective characteristics with low homogeneity and high tendency to tear.

Diameter

Diameters of the extruded cylinder strands varied from 247 to 371 [micro] m, and the C25 strand had the highest value followed by C20. These two formulations contained only starch and glycerol. After exiting the extruder, these formulations experience greater expansion than the others. The diameter of the extruded cylinders did not correlate with the glycerol concentration.

The extruded strands that were similar to the standard PBAT formulation were the formulations the contained caproic acid, likely due to the better plasticization caused by caproic acid when compared with the other fatty acids. Formulation El28 was also similar to the standard, but its extruded strands were more rigid and fragile, which has been previously reported.

Mechanical Tension Tests

The control formulation with 12.8% glycerol, CI28, did not support the mechanical test conditions, since the samples were very rigid and fragile. The tension tests were performed on the [C.sub.a] l28, [L.sub.a] l28, and E128 formulations, since these formulations possessed characteristics that were different compared with the formulations that contained 20% or 25% glycerol. As such, these formulations were compared separately. Table 3 shows the results of the mechanical tests in terms of maximum tension (T), elongation at rupture ([epsilon]), and Young's modulus (Y) for the extruded cylinder strands.

The formulations [C.sub.a] l28, [L.sub.a] 128, and El28 presented maximum tensile resistance values nearly 10 times greater than the values presented by the formulations with 25% glycerol. These samples also presented elongations at rupture that ranged from 2% to 10%, which was 30 times lower than the other formulations. The values of the Young's modulus were between 288 and 537 MPa, which was roughly 25 times greater than the greatest value of the other formulations.

The strand extruded with caproic acid ([C.sub.a] l28) presented the greatest resistance to tension and greatest elongation in relation to the other formulations. The strands [L.sub.a] 128 and El28 presented a lower elongation, probably due to the greater compatibility of starch with the shorter chain fatty acid ([C.sub.a]). This compatibility decreased with the increase in the carbonic chain of the fatty acid due to its non-polar characteristics, which were reflected in the mechanical properties of the extruded strands. This incompatibility between starch and the long chain fatty acids may generate weaker blends with poorer mechanical properties.

The maximum tension of the extruded strands varied from 0.7 MPa to 3.2 MPa. Tension is linked to plasticization of starch; a TPS with greater plasticization presents lower tension due to its lower rigidity and greater chain mobility in the structure. An increase in the concentration of glycerol from 20% to 25% caused a decrease in the resistance to tension by approximately 7% for the control formulation and 60% for the formulations with fatty acids. The formulation presenting the greatest reduction was the one that contained lauric acid, where there was a reduction of 65% from formulation [L.sub.a] 20 to [L.sub.a] 25.

Plasticization modified the mechanical properties of the materials by reducing the maximum force and increasing elongation. Therefore, the plasticization effect of the fatty acids was not demonstrated by the mechanical properties of the extruded strands. This result may be due to the low interactions between starch and the studied fatty acids, which could have generated mechanically weaker materials with lower elongations.

A possible explanation for the trends in maximum force and elongation of the extruded strands may be related to hydroxyl groups (OH) and fatty acid molar mass. The hydroxyl groups directly influence plasticization. Therefore, the formulations containing caproic acid had one OH group per mole of acid (116.16 g). The formulations with lauric acid had one OH per 200.32 g, and the formulation with stearic acid had one OH group per 284.48 g. For the same mass of fatty acid, the formulations containing caproic acid presented the greatest quantity of hydroxyl groups per mass and thus had greater plasticization.

Only the control presented an increase in the value of elongation at ruptures with an increase in the glycerol concentration from 20% to 25%. The strands extruded with fatty acids presented a reduction of approximately 35% in elongation when the glycerol concentration increased from 20% to 25%, which apparently contradicted the affirmation that greater glycerol concentrations facilitated movement of starch chains, thereby increasing film flexibility (1). However, the Young's modulus decreased with an increase in the glycerol content from 20% to 25%, indicating a reduction in rigidity by roughly 64% of the extruded strands containing fatty acids. This occurred do to an increase in glycerol concentration, which reduced the maximum tension by roughly 60%, whereas the reduction in the control (C) was only 7%. The increase in glycerol concentration drastically reduced the mechanical resistance and the elongation at break of the strands containing fatty acids, probably due to an incompatibility among the polar components and the fatty acids that decreased the interactions between the starch chains and weakened the polymer matrix.

Because the mechanical properties of the extruded strands differed significantly from the PBAT formulation, which served as a reference for film formation, it was not possible, based on the studied formulations, to predict from these properties if a film would form. Despite the differences between the formulations containing fatty acids and the standard, all the formulations were capable of film forming (Table 2).

Mechanical Shear Stress Tests

The maximum values of resistance to shear stress (F) for the extruded cylinder strands are presented in Table 3. The maximum resistance to shear stress varied from 7.6 to 36.5 MPa. The strands with 12.8% glycerol presented the greatest resistance to shear force and were the most rigid, as described previously. These strands also did not present the necessary characteristics to perform all of the tests. There was a trend in the reduction of the resistance to shear force with an increase in the glycerol concentration of the extrusions, which may be associated with the plasticization effect of glycerol that occurs when it is added to starch (18), (19).

The addition of fatty acids resulted in a decrease in the resistance to shear force, characterizing the plasticizing effect of the fatty acids. However, the size of the carbonic chain in the fatty acids did not influence this parameter. The maximum shear stress remained within 7.6 MPa for the addition of six carbon fatty acids (caproic acid) and 12.8 MPa for the addition of stearic acid (18C).

The strand of the PBAT presented a greater resistance to shear force than the other formulations, since PBAT provided resistance to the extruded strand as well as the film formed during the extrusion process. The incorporation of this polymer into the extruded strands containing fatty acids would probably result in an increase in resistance to shear stress.

Maximum Strain and Relaxation Percentage

The maximum strain was selected as 1% of the length of the sample due to the linear behavior of the force in the function of elongation in this range. In this region, the specimen suffered deformation with the applied strain, and when the force was removed, the specimen returned to its initial state.

Figure 2 shows the relaxation curves for the strands containing 20% and 25% glycerol in the formulation as well as the standard (PPBAT). All of the strands were conditioned at 53% RH. Initially, an ascending curve obtained by the imposition of a constant deformation rate was noticed; subsequently, it was observed that the force necessary to maintain deformation declined with time. This behavior is characteristic of viscoelastic materials (17), (20),

[FIGURE 2 OMITTED]

Table 4 presents the results of maximum force (F0) and the deformation percentages for the formulations with 20% and 25% glycerol. The relaxation force is associated not only with the intrinsic characteristics of the material but also with the conditions during the test, which makes a comparison with other results found in the literature difficult. Viscoelastic characteristics were also observed in biofilms by Muller et al. (8), who studied the incorporation of cellulose fibers in starch films produced through casting. Similarly, Cuq et al. (21) and Chandra and Sobral (20) studied myofibrillar protein films. However, no data was encountered in the literature for the viscoelastic strands of extruded strands.

For the extrusions containing 20% glycerol in the formulation, the encountered maximum force ([F.sub.0]) values varied from 3.7 to 9.5 N. The forces of extruded strands [C.sub.a] 20 and E20 were nearly equal. However, formulation La20 presented a lesser force among the analyzed formulations that was nearly three times less than the force presented by the control formulation (C20).

The maximum force was related to the plasticizing effect of the different fatty acids, and therefore it may be inferred that lauric acid has a greater plasticizing effect than the stearic and caproic acids. The same behavior may be observed for the formulations with 25% glycerol. The maximum force of the [L.sub.a] 25 strands differed from the other formulations. These formulations had values less than half the force presented by formulations [C.sub.a] 25 and E25, and roughly 10 times less than the force values for the control (C25).

In general, the formulations with 25% glycerol presented a lower maximum force, a behavior that may be associated with the increase in plasticization of the extruded strands that paralleled the increase in glycerol content. The results of the relaxation percentage indicated that the PBAT sample presented a lower decrease in force relative to the initial force compared with the other studied formulations. This behavior was indicative of the more pronounced elastic characteristics in this sample.

According to Peleg [17], the value (1 - [C.sub.1]) may be considered a degree of solidity, whereas ([C.sub.1]/ [C.sub.2]) is the initial relaxation rate. When (1 - [C.sub.1]) approaches one, the material behaves as an elastic solid. When this value approaches zero, the material behaves as a viscous liquid. Values of the constants for the model are presented in Table 5.

With the exception of formulation [C.sub.a] 25, the addition of 1.5% fatty acids did not appear to influence the degree of solidity (1 - [C.sub.1]). In other words, the fatty acids did not alter the viscoelastic character of the extruded strands. Strand [C.sub.a] 25 was the formulation that presented the best elastic characteristic (0.35) within the proposed formulation. This behavior may be due to the interaction between the smaller carbonic chain and starch.

The PBAT strand was more elastic with a greater value of (1 - [C.sub.1]), which was 0.67 according to the results of the relaxation percentage. This high value may be an indicator of the characteristics extruded strands should have for the formation of films through blown extrusion.

The initial relaxation rate, characterized by the value of ([C.sub.1]/ [C.sub.2]), was influenced by three factors: glycerol concentration, presence of fatty acids, and the size of the fatty acids that were present. When this value approached zero, the material presented a lower relaxation, further resisting the force to which it was submitted. The ([C.sub.1]/ [C.sub.2]) values of the extruded strands decreased by approximately 18% when the glycerol concentration increased from 20% to 25%, which may be due to the plasticizing effects of glycerol (18), (19).

Among the formulations containing fatty acids, those with caproic acid presented lower initial relaxation rates, likely due to the greater interaction between caproic acid and starch. The formulations containing lauric and stearic acid presented greater initial relaxation rates, and this result may be related to the greater hydrophobic characteristics of these components as well as the minimal interaction between these components and starch, which makes up the polymer matrix.

The PBAT extruded strand presented the lowest value for the initial relaxation rate (0.29) and presented greater elasticity. Therefore, the PBAT strand is better able to withstand the applied force. Similar to the degree of solidity, the value of the initial relaxation rate may be an indicator of film formation.

CONCLUSIONS

It was not possible to correlate the properties of the extruded strands from the mechanical tests of maximum tension, elongation at break, and maximum resistance to film formation via blown extrusion. The viscoelastic characteristics (initial rate and percentage of relaxation and degree of solidity) are determinant in the processability of polymer blends studied with the goal of film formation by blown extrusion.

ACKNOWLEDGMENTS

The authors acknowledge CAPES, CNPq, and the Araucaria Foundation for their financial support as well as the Postdoctoral and Productivity in Research scholarship program.

REFERENCES

(1.) X. Tang, S. Alavi, and T.J. Herald, Carbohydr. Polym., 74, 552 (2008).

(2.) J. Ren, H. Fu, T. Ren, and W. Yuan, Carbohydr. Polym., 77, 576 (2009).

(3.) S. Mali, M.V.E. Grossmann, and F. Yamashita, Semina-Ciencias Agrarias, 31, 137 (2010).

(4.) R. Chandra and R. Rustgi, Polym. Degrad. Stab., 56, 185 (1997).

(5.) A. Rouilly and L. Rigal, J. Macromol. Sci. Polym. Rev., 42, 441 (2002).

(6.) C.M.O. Muller, F. Yamashita, and J.B. Laurindo, Carbohydr. Polym., 72, 82 (2008).

(7.) C.M.O. Muller, J.B. Laurindo, and F. Yamashita, Food Hydrocoll., 23, 1328 (2009).

(8.) C.M.O. Muller, J.B. Laurindo, and F. Yamashita, Carbohydr. Polym., 77, 293 (2009).

(9.) F.A.B. Ferreira, M.V.E. Grossmann, F. Yamashita, and L.P. Cardoso, Braz. Arch. Biol. Techno?., 52, 1505 (2009).

(10.) M.C. Galdeano, S. Mali, M.V.E. Grossmann, F. Yamashita, and M.A. Garcia, Mater. Set. Eng. C, 29, 532 (2009).

(11.) A.P. Bilck, M.V.E. Grossmann, and F. Yamashita, Polymer Test., 29,471 (2010).

(12.) M.R.S. Scapim, Producao, caracterizacao, aplicacao e biode-gradabilidade de filmes de blendas de amido e poli (butileno adipalo co-tereftalato) produzidos por extrusao, Londrina Tese de doutorado (Doulorado em Ciencia de Alimentos), Univcrsidade Estadual de Londrina, 2009.

(13.) D.L.M.G. Costa, Producao por extrusao de filmes de alto teor de amido termoplastico de mandioca com poli (butileno adipato co-tereftalato) (PBAT). Londrina Dissertacao de mestrado (Mestrado em Ciencia e Tecnologia de Alimentos), Universidade Estadual de Londrina, 2008.

(14.) R.P.H. Brandelero, F. Yamashita, and M.V.E. Grossmann, Carbohydr. Polym., 82, 1102 (2010).

(15.) L. Averous and C. Fringant, Polym. Eng. Sci., 41, 727 (2001).

(16.) F.M. Fakhouri, L.C.B. Fontes, L.H. Innocentini-Mei, and F.P. Collares-Queiroz, Starch Starke, 61, 528 (2009).

(17.) M. Peleg, J. Food Sci., 44, 277 (1979).

(18.) Y.P. Chang, A.A. Karim, and C.C. Seow, Food Hydrocoll., 20, 1 (2006).

(19.) S. Mali, L.S. Sakanaka, F. Yamashita, and M.V.E. Grossmann, Carbohydr. Polym., 60, 283 (2005).

(20.) P.K. Chandra and P.J.d.A. Sobral, Ciencia e Tecnologia de Alimentos, 20, 250 (2000).

(21.) B. Cuq, N. Gontard, J.L. Cuq, and S. Guilbert, J. Agric. Food Chem., 44, 1116 (1996).

Marcelo Medre Nobrega, (1) Evandro Bona, (2) Carmen Maria Olivera Muller, (1) Fabio Yamashita (1)

(1) Department of Food Science and Technology, State University of Londrina, P.O. Box 6001, C.E.P. 86051-990, Londrina, PR, Brazil

(2) Post-Graduation Program of Food Technology (PPGTA), Federal University of Technology - Parana (UTFPR), P.O. Box 271, C.E.P. 87301-006, Campo Mourao, PR, Brazil

Correspondence to: Marcelo Medre Nobrega; e-mail: marcelo.medre@ gmail.com

DOl 10.1002/pen.2204l
TABLE 1. Formulations of the extruded strands.

Formulation   Fatty   Fatty   Starch   Glycerol  PBAT
               acid     acid     (%)       (%)     (%)
                         (%)

PPBAT        --       --       37.5      12.5    50

C128         --                86.9      13.1    --

C20          --       --         80        20    --

C25          --       --         75        25    --

[C.sub.a]    Caproic    1.5    85.7      12.8    --
l28

[C.sub.a]    Caproic    1.5    78.8      19.7    --
20

[C.sub.a]    Caproic    1.5    73.9      24.6    --
25

[L.sub.a]    Laurie     1.5    85.7      12.8    --
l28

[L.sub.a]    Laurie     1.5    78.8      19.7    --
20

[L.sub.a]    Laurie     1.5    73.9      24.6    --
25

E128         Stearic    1.5    85.7      12.8    --

E20          Stearic    1.5    78.8      19.7    --

E25          Stearic    1.5    73.9      24.6    --


TABLE 2. Subjective evaluation of films made of starch,
glycerol, and PBAT with the addition of fatty acids.

Film          Film forming  Homogeneity  Handling  Tendency
                                                    to tear

PPBAT         Yes           XXX          XXX       No
C20           Yes           XX           XXX       No
C25           Yes           XXX          XXX       No
[C.sub.a] 20  Yes           XXX          XXX       No
[C.sub.a] 25  Yes           XXX          XXX       No
[L.sub.a] 20  Yes           XXX          XXX       No
[L.sub.a] 25  Yes           XXX          XXX       No
E20           Yes           X            XXX       Yes
E25           Yes           X            XXX       Yes

PPBAT - extruded with 50% PBAT and 25% glycerol in
relation to 50% starch. C20 and C25 - films with 30%
of PBAT, 20% and 25% of glycerol compared with 70% of
thermoplastic starch, respectively.[C.sub.a] 20,
[C.sub.a] 25, [L.sub.a] 20, [L.sub.a] 25, E20, and
E25 - films with 30% of PBAT, 20$ and 25% of glycerol
compared with TPS and 1.5% of caproic, lauric, and
stearic acid, respectively, x - deficient, xx - good,
and xxx - excellent.


TABLE 3. Maximum tension (7), elongation at rupture
(member of). Young's modulus (10, and Maximum shear
stress (F) of the extruded strands composed of starch
and glycerol with the addition of fatty acids.

Formulation    T [(MPa).                         Y            F
                sup.a]        [pounds
                                            [(MPa)       [(MPa).
                             Sterling]                     sup.a]
                            [(%).sup.a]     .sup.a]

PPBAT         4.4 [+ or-]   189 [+ or -]   20[+ or -]  19.4[+ or-]
              [0.1.sup.a]     [25.sup.a]    [1.sup.a]  [1.2.sup.c]

C20             1.5 [+ or   106 [+ or -]   5 [+ or -]  12.0[+ or-]
                       -]
              [0.0.sup.e]    [6.sup.b,c]    [0.sup.e]  [0.4.sup.d]

C25            1.4[+ or-]   119 [+ or -]    4[+ or -]  11.6[+ or-]
              [0.0.sup.e]      [4.sup.b]    [0.sup.e]  [0.3.sup.d]

[C.sub.a]     1.9 [+ or-]   108 [+ or -]    7[+ or -]   7.6[+ or-]
20
              [0.0.sup.d]    [8.sup.b,c]    [0.sup.d]  [0.2.sup.f]

[C.sub.a]      0.7[+ or-]    74 [+ or -]    2[+ or -]   8.7[+ or-]
25
              [0.0.sup.g]    [2.sup.c,d]    [0.sup.f]  0.3.sup.e,f

[L.sub.a]     3.2 [+ or-]    87 [+ or -]   14[+ or -]  14.1[+ or-]
20
              [0.0.sup.b]  [2.sup.b,c,d]    [0.sup.b]  [0.3.sup.d]

[L.sub.a]      1.1[+ or-]    59 [+ or -]    4[+ or -]   8.3[+ or-]
25
              [0.0.sup.f]      [2.sup.d]  [0.sup.e,f]  [0.1.sup.f]

E20           2.4 [+ or-]    90 [+ or -]    8[+ or -]  12.8[+ or-]
              [0.0.sup.c]  [2.sup.b,c,d]    [0.sup.c]  [0.3.sup.d]

E25           1.0 [+or -]    58 [+ or -]    4[+ or -]   8.3[+ or-]
              [0.1.sup.f]      [3.sup.d]  [0.sup.e,f[  [0.3.sup.f]

[C.sub.a]    14.3 [+ or-]    10 [+ or -]   362[+ or-]  24.4[+ or-]
l28                                    1
                      0.2                          16  [0.5.sup.b]

[L.sub.a]    13.9 [+ or-]     2 [+ or -]   537[+ or-]  36.5[+ or-]
l28
                      1.2              0           44  [2.7.sup.a]

E128           8.4[+ or-]      3[+ or -]   288[+ or-]   26.9[+or-]
                      1.1              0           42  [0.9.sup.b]

PPBAT - extruded with 50% PBAT and 25% glycerol in relation
to 50% starch. C20 and C25 - extruded with 20% and 25%
glycerol in relation to starch, respectively. [C.sub.a]
20, [C.sub.a] 25, [L.sub.a ]20, [L.sub.a] 25, E20, and
E25 -extruded with 20% and 25% glycerol in relation to
starch and 1.5% caproic, lauric, and stearic acid,
respectively. Cal28, La 128, and El28 -extruded with
12.8% glycerol in relation to starch and 1.5% caproic,
lauric, and stearic acid, respectively.

(a) Averages with the same letters in the same column
did not present significant differences in the Tukey
test (p < 0.05).


TABLE 4. Maximum force (F0) and relaxation percentage
of strands extruded from cassava starch and fatty acids.

Formulation      %          [F.sub.0]             %
             glycerol    [(N).sup.a]    [relaxation.sup.a]

C                  20     9.5 [+ or -]         81 [+ or -]
                           [0.7.sup.a]         [2.sup.a,b]
                   25     9.7 [+ or -]         73 [+ or -]
                           [0.8.sup.a]         [1.sup.b,c]

[C.sub.a]          20     6.4 [+ or -]         70 [+ or -]
                           [0.3.sup.b]         [3.sup.b,c]
                   25     2.2 [+ or -]         65 [+ or -]
                         [0.1.sup.d,e]           [1.sup.c]

[L.sub.a]          20     3.7 [+ or -]         86 [+ or -]
                         [0.2.sup.c,d]           [4.sup.a]
                   25     0.9 [+ or -]         78 [+ or -]
                           [0.1.sup.e]         [3.sup.a,b]

E                  20     5.5 [+ or -]         80 [+ or -]
                         [0.3.sup.b,c]         [2.sup.a,b]
                   25     2.2 [+ or -]         70 [+ or -]
                         [0.1.sup.d,e]         [2.sup.b,c]

PPBAT              25        4.8 [+ or         32 [+ or -]
                       -][0.3.sup.b,c]           [2.sup.d]

C - starch extrusions with 20% and 25% glycerol. [C.sub.a],
[L.sub.a], and E -starch extrusions with 20% and 25%
glycerol in relation to TPS and 1.5% caproic, lauric,
and stearic acid, respectively. PPBAT - starch extrusion
with 50% PBAT and 25% glycerol in relation to TPS.

(a) Averages with the same letters in the same column
did not present significant differences in the Tukey
test (p < 0.05).


TABLE 5. Parameters of the Peleg model for relaxation
tests of the extruded starch strands with addition of
fatty acids, conditioned at 53% relative humidity.

                            Parameters
Formulation  % glycerol  [(1 - [C.sub.1])      [([C.sub.1]/
                             .sup.a]       [C.sub.2]).sup.a] (s)

C                    20     0.18 [+ or -]          0.96 [+ or -]
                           [0.02.sup.c,d]         [0.04.sup.b,c]
                     25     0.27 [+ or -]          0.83 [+ or -]
                           [0.01.sup.b,c]         [0.02.sup.d,e]

[C.sub.a]            20     0.29 [+ or -]          0.85 [+ or -]
                           [0.03.sup.b,c]         [0.01.sup.c,d]
                     25     0.35 [+ or -]          0.72 [+ or -]
                             [0.02.sup.b]           [0.02.sup.e]

[L.sub.a]            20     0.14 [+ or -]          1.19 [+ or -]
                             [0.04.sup.d]           [0.03.sup.a]
                     25     0.22 [+ or -]          0.96 [+ or -]
                           [0.03.sup.c,d]         [0.03.sup.b,c]

E                    20     0.19 [+ or -]          0.98 [+ or -]
                           [0.03.sup.c,d]           [0.01.sup.b]
                     25     0.29 [+ or -]          0.73 [+ or -]
                           [0.02.sup.b,c]           [0.01.sup.e]

PPBAT                25     0.67 [+ or -]          0.29 [+ or -]
                             [0.02.sup.a]           [0.01.sup.f]

C - starch extrusions with 20% and 25% glycerol. [C.sub.a],
[L.sub.a], and E -starch extrusions with 20% and 25% glycerol
in relation to TPS and 1.5% caproic, lauric, and stearic acid,
respectively. PPBAT - starch extrusion with 50% PBAT and 25%
glycerol in relation to TPS.

(a) Averages with the same letters in the same column did not
present signification differences in the Tukey test (p < 0.05).
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