**5. Results and discussion**

Comparison of mechanical properties of organic-inorganic hybrids and cellulose acetate butyrate with different plasticizers is shown in Table 2 and Figures 1-18.


Table 2. Mechanical properties of CAB samples containing various plasticizers.

Comparison of mechanical properties of organic-inorganic hybrids and cellulose acetate

Tensile strength (MPa)

TEA 25 24.9 ± 0.5 7.0 ± 0.4 23.0 ±1.3 16.2 ± 1.1 20.1 ± 1.5 26.3 ± 3.0

TEA 30 24.9 ± 1.1 37.8 ± 8.5 23.1 ± 1.3 44.8 ± 9.1 21.6 ± 1.0 34.3 ± 6.1

TEA 35 21.2 ± 1.4 45.6 ± 5.4 21.8 ± 0.8 53.6 ± 4.1 20.4 ± 0.7 48.7 ± 1.1

TBC 25 17.4 ± 0.7 16.7 ± 4.1 16.4 ± 0.4 13.9 ± 1.4 15.5 ± 1.7 24.3 ± 2.3

TBC 30 25.3 ± 2.8 40.9±13.6 23.6 ± 2.5 42.4 ± 7.6 21.8 ± 2.3 30.2 ± 6.9

TBC 35 15.7 ± 1.5 53.1 ± 8.4 14.3 ± 0.8 53.9 ± 2.1 13.4 ± 1.0 38.1 ± 4.4

TEC 25 24.0 ± 0.8 5.0 ± 0.6 17.0 ± 1.6 7.6 ± 1.1 21.5 ± 0.8 14.7 ± 2.4

TEC 30 14.4 ± 0.1 25.8 ± 1.6 13.3 ± 0.4 21.6 ± 3.5 12.7 ± 0.5 29.0 ± 6.3

TEC 35 12.8 ± 0.3 29.3 ± 4.2 11.5 ± 0.3 25.8 ± 0.8 11.2 ± 0.4 32.0 ± 3.8

DEP 25 15.9 ± 0.5 5.5 ± 0.9 13.8 ± 1.7 5.5 ± 0.3 12.5 ± 1.5 8.7 ± 1.7

DEP 30 20.9 ± 0.8 16.3 ± 1.5 19.2 ± 1.1 14.0 ± 2.0 17.6 ± 1.0 10.6 ± 1.7

DEP 35 21.7 ± 1.1 19.9 ± 0.4 17.4 ± 0.9 15.0 ± 3.0 14.1 ± 0.9 17.8 ± 0.6

DBP 25 23.2 ± 1.7 19.3 ± 3.5 20.5 ± 1.6 23.6 ± 2.8 21.0 ± 1.7 25.5 ± 2.5

DBP 30 26.4 ± 0.8 33.9 ± 5.0 25.0 ± 0.6 35.6 ± 4.6 24.8 ± 0.3 31.8 ± 5.5

DBP 35 20.3 ± 0.7 48.6 ± 5.6 16.4 ± 0.5 36.1 ± 3.1 14.6 ± 0.2 37.2 ± 2.8

DOP 25 27.3 ± 2.8 28.7 ± 0.4 23.7 ± 1.6 21.4 ± 1.7 22.3 ± 1.6 13.8 ± 2.8

DOP 30 31.1 ± 1.2 52.1 ± 1.5 28.1 ± 2.5 42.5 ± 4.5 28.3 ± 1.8 34.3 ± 2.0

DOP 35 23.5 ± 3.9 50.1 ± 3.3 19.9 ± 2.1 40.4 ± 6.1 16.7 ± 1.1 38.0 ± 5.0

Table 2. Mechanical properties of CAB samples containing various plasticizers.

Polymer/TEOS ratio

Elongation at break (%)

Tensile strength (MPa)

Elongation at break (%)

87.5/12.5 93.75/6.25 100

butyrate with different plasticizers is shown in Table 2 and Figures 1-18.

Elongation at break (%)

**5. Results and discussion** 

Tensile strength (MPa)

Type of the plasticizer The aim of adding plasticizer to CAB-hybrids is to reduce natural brittleness of the polymer and to enhance plastic elongation, while providing optimal tensile strength and stiffness.

The plasticizing efficiency of the investigated phthalates and citrates evaluated by tensile testing is summarized in Table 2. At concentration 25% samples of the cellulose acetate butyrate plasticized with TEA, TEC, DBP and DOP exhibited similar tensile strength in the range of 20 – 22 MPa, however high values of elongation at break (24 – 26%) showed only samples containing TBC, DBP and TEA. In case of CAB hybrids the introduction of inorganic phase into polymer matrix caused hardening and reinforcing of the material, thus an increase of tensile strength in comparison with unmodified CAB was observed. Regarding organic-inorganic hybrids prepared from 93.75/6.25 and 87.5/12.5 polymer/TEOS formulations the highest values of tensile strength (23 – 24 MPa and 25 – 27 MPa) were obtained for samples 6.25TEA25, 6.25DOP25, and 12.5TEA25, 12.5DOP25, respectively. However, at the same time, obtained samples exhibited lower values of elongation at break as compared with plasticized CAB, due to the higher brittleness of the material. The results showed that the presence of 25% of plasticizer in organic-inorganic CAB hybrids was insufficient for providing acceptable flexibility.

Considering the effect of plasticizer concentration it can be concluded that all of the plasticizers investigated, excluding TEC, caused an antiplasticization at concentration 30% of the plasticizer, resulting in an increase in tensile strength in comparison with the values at 25%. To the contrary, samples plasticized with TEC showed a common trend: with increasing plasticizer content, the tensile strength decreased, while elongation at break increased. Antiplasticizing effects were previously observed by Donempudi et al. for PVC membranes plasticized with phthalates [37], reported for citrate esters used as plasticizers for poly(methyl methacrylate) (PMMA) [38], and also has been found for polycarbonate, polysulfone, polystyrene plasticized with various plasticizers [39]. Even though the phenomenon of antiplasticization has been already long observed in synthetic polymers, the mechanisms involved are not perfectly known. According to Anderson et al. the phenomenon can be attributed to a chain end effect. Antiplasticizers initially fill unoccupied lower volume at the chain end and then the overall polymer free volume. Chain end mobility is restricted, resulting, thus, in higher modulus and resistance, generally followed by polymer hardness. Jackson and Caldwell suggested that antiplasticization can be attributed to a free volume reduction due to antiplasticizers [40]. Another explanation is an increase in the degree of order or the crystallinity of the system, resulting in an increase in tensile strength. Antiplasticization of the samples may be attributed to the hindered local mobility of the macromolecules, and thus reduced flexibility, due to the strong interaction between polymer and plasticizer (i.e. hydrogen bonding, van der Waals' forces) [39, 41]. Antiplasticization in polymers depends on molecular weight and concentration of the diluent and occurs over a concentration range below the plasticization threshold. This point, dividing antiplasticization and plasticization behavior, is typical for each polymer– plasticizer system [42]. Gutierrez-Villarreal [38] reported an antiplasticization effect for PMMA plasticized with TEC at low concentration of plasticizer (about 13 wt%). The plasticization threshold for TEC plasticized samples based on CAB was not observed in the range of concentrations used in this study. For the samples prepared with lower concentration of TEC (below 25%) the measurement using a universal tensile machine was

The Effect of Concentration and Type of Plasticizer

than for the plasticized CAB.

0

5

10

15

[MPa]

20

25

30

containing longer alkyl groups was found to be the most efficient.

Fig. 1. The tensile stress-strain curves for samples prepared with 25% of TEA.

0 5 10 15 20 25 30

[%]

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 151

an increased dilution of the polymer solution. Hence, the high molecular weight implied a further reduction in the number of macromolecules per unit volume. Therefore, the use of higher concentration of larger size phthalate molecules in the PVC matrix caused significant dilution effect, and as a result an increase in the flexibility of the polymer [37]. Similar results were obtained also for citrate plasticizers applied in the study. The lowest plasticizing efficiency of TEC, among citrate plasticizers used in this work, may be attributed to its low molecular weight. On the contrary, the highest molecular weight TBC,

The stress-strain curves for the samples prepared with different plasticizers are presented in Fig. 1-18. The characteristic type of the curve for hard and rigid materials, exhibiting low values of elongation at break, showed organic-inorganic hybrids prepared with 25% of TEC and DEP (Figure 7, 10). Hard, tough behaviour is observed for the samples exhibiting sufficient and good plasticizing efficiency (Fig. 1-6, 8, 9, 11-18). All the curves showed cold drawing and strain hardening in the final section of the curve. However, for the samples prepared from the formulations exhibiting the best mechanical properties, the curves showed better defined yielding point. In case of organic-inorganic hybrids with the highest content of inorganic phase the curves exhibited elastic deformation in smaller strain ranges

> 12.5TEA25 6.25TEA25 TEA25

difficult to perform due to the high brittleness of the organic-inorganic hybrids (cutting of the samples might induce micro-cracking on the edge of the samples and influence the reliability of the test results).

Considering the fact that different factors may be involved in the antiplasticization phenomenon, the present study was not designed to provide evidence in support of any one of these mechanisms. Further experiments including dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) or X-ray measurements could confirm suggested hypothesis.

At concentration 30% the CAB samples plasticized with DOP and DBP showed the highest tensile strength (28.3 MPa and 24.8 MPa, respectively). Among citrate plasticizers the higher tensile strength values were obtained for CAB samples plasticized with TBC and TEA (21.8 MPa and 21.6 MPa, respectively). The lowest values of tensile strength showed CAB samples plasticized with TEC (12.7 MPa) and DEP (17.6 MPa) due the high brittleness of the material, indicating low plasticizing efficiency of those plasticizers. Interestingly, organicinorganic hybrids showed both high values of tensile strength, regardless of the plasticizer type and concentration, as well as elongation at break in comparison with plasticized CAB. Organic-inorganic hybrid prepared from 87.5/12.5 polymer/TEOS formulation and DOP (12.5DOP30) exhibited the highest tensile strength (31.1 MPa) as well as very high elongation at break (52.1%). Regarding the citrate plasticizers at 30% concentration the best mechanical properties were obtained for TBC and TEA. In this case, organic-inorganic hybrids prepared from 87.5/12.5 polymer/TEOS formulation plasticized with TBC and TEA showed similar values of tensile strength and elongation at break: 25.3 MPa and 40.9%, and 24.9 MPa and 37.8% , respectively.

At higher concentration of plasticizers used in this study (35%) the additives caused plasticization reflected as a decreases in tensile strength and an increase in elongation at break values. Regarding CAB samples, the highest values of elongation at break showed material plasticized with TEA (48.7%). Among phthalates, at level of 35%, the highest value of elongation at break CAB reaches for DOP and DBP (38.4% and 37.2%, respectively). The highest values of elongation at break for the organic-inorganic hybrids obtained from 93.75/6.25 polymer/TEOS formulation were observed for samples plasticized with TBC, TEA and DOP (53.9%, 53.6% and 40.4%, respectively). In case of organic-inorganic hybrids obtained from 87.5/12.5 polymer/TEOS formulation the highest values of elongation at break provided TBC, DOP and DBP plasticizers (53.1%, 50.1% and 48.6%, respectively).

If one considers the effect of plasticizer molecular weight on the mechanical properties of investigated samples, one might conclude that the higher molecular weight, the better efficiency of the plasticizer. Regarding phthalate esters, plasticizer with the lowest molecular weight produced the less flexible samples and the efficiency varied in the order DEP>DBP>DOP. Similar behavior was previously observed for phthalate esters used as plasticizers for PVC membranes [37]. Donempudi at al. found that the tensile strength of the membranes decreased as the size of the alkyl group of the phthalate molecule increased from methyl to octyl, meanwhile the elongation at break values increased. They referred that an increase in the size of the alkyl chain length of the phthalate molecule brought about

difficult to perform due to the high brittleness of the organic-inorganic hybrids (cutting of the samples might induce micro-cracking on the edge of the samples and influence the

Considering the fact that different factors may be involved in the antiplasticization phenomenon, the present study was not designed to provide evidence in support of any one of these mechanisms. Further experiments including dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) or X-ray measurements could confirm suggested

At concentration 30% the CAB samples plasticized with DOP and DBP showed the highest tensile strength (28.3 MPa and 24.8 MPa, respectively). Among citrate plasticizers the higher tensile strength values were obtained for CAB samples plasticized with TBC and TEA (21.8 MPa and 21.6 MPa, respectively). The lowest values of tensile strength showed CAB samples plasticized with TEC (12.7 MPa) and DEP (17.6 MPa) due the high brittleness of the material, indicating low plasticizing efficiency of those plasticizers. Interestingly, organicinorganic hybrids showed both high values of tensile strength, regardless of the plasticizer type and concentration, as well as elongation at break in comparison with plasticized CAB. Organic-inorganic hybrid prepared from 87.5/12.5 polymer/TEOS formulation and DOP (12.5DOP30) exhibited the highest tensile strength (31.1 MPa) as well as very high elongation at break (52.1%). Regarding the citrate plasticizers at 30% concentration the best mechanical properties were obtained for TBC and TEA. In this case, organic-inorganic hybrids prepared from 87.5/12.5 polymer/TEOS formulation plasticized with TBC and TEA showed similar values of tensile strength and elongation at break: 25.3 MPa and 40.9%, and

At higher concentration of plasticizers used in this study (35%) the additives caused plasticization reflected as a decreases in tensile strength and an increase in elongation at break values. Regarding CAB samples, the highest values of elongation at break showed material plasticized with TEA (48.7%). Among phthalates, at level of 35%, the highest value of elongation at break CAB reaches for DOP and DBP (38.4% and 37.2%, respectively). The highest values of elongation at break for the organic-inorganic hybrids obtained from 93.75/6.25 polymer/TEOS formulation were observed for samples plasticized with TBC, TEA and DOP (53.9%, 53.6% and 40.4%, respectively). In case of organic-inorganic hybrids obtained from 87.5/12.5 polymer/TEOS formulation the highest values of elongation at break provided TBC, DOP and DBP plasticizers (53.1%,

If one considers the effect of plasticizer molecular weight on the mechanical properties of investigated samples, one might conclude that the higher molecular weight, the better efficiency of the plasticizer. Regarding phthalate esters, plasticizer with the lowest molecular weight produced the less flexible samples and the efficiency varied in the order DEP>DBP>DOP. Similar behavior was previously observed for phthalate esters used as plasticizers for PVC membranes [37]. Donempudi at al. found that the tensile strength of the membranes decreased as the size of the alkyl group of the phthalate molecule increased from methyl to octyl, meanwhile the elongation at break values increased. They referred that an increase in the size of the alkyl chain length of the phthalate molecule brought about

reliability of the test results).

24.9 MPa and 37.8% , respectively.

50.1% and 48.6%, respectively).

hypothesis.

an increased dilution of the polymer solution. Hence, the high molecular weight implied a further reduction in the number of macromolecules per unit volume. Therefore, the use of higher concentration of larger size phthalate molecules in the PVC matrix caused significant dilution effect, and as a result an increase in the flexibility of the polymer [37]. Similar results were obtained also for citrate plasticizers applied in the study. The lowest plasticizing efficiency of TEC, among citrate plasticizers used in this work, may be attributed to its low molecular weight. On the contrary, the highest molecular weight TBC, containing longer alkyl groups was found to be the most efficient.

The stress-strain curves for the samples prepared with different plasticizers are presented in Fig. 1-18. The characteristic type of the curve for hard and rigid materials, exhibiting low values of elongation at break, showed organic-inorganic hybrids prepared with 25% of TEC and DEP (Figure 7, 10). Hard, tough behaviour is observed for the samples exhibiting sufficient and good plasticizing efficiency (Fig. 1-6, 8, 9, 11-18). All the curves showed cold drawing and strain hardening in the final section of the curve. However, for the samples prepared from the formulations exhibiting the best mechanical properties, the curves showed better defined yielding point. In case of organic-inorganic hybrids with the highest content of inorganic phase the curves exhibited elastic deformation in smaller strain ranges than for the plasticized CAB.

Fig. 1. The tensile stress-strain curves for samples prepared with 25% of TEA.

The Effect of Concentration and Type of Plasticizer

0

0

5

10

15

[MPa]

20

25

30

2

4

6

8

10

[MPa]

12

14

16

18

20

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 153

 12.5TBC25 6.25TBC25 TBC25

 12.5TBC30 6.25TBC30 TBC30

Fig. 4. The tensile stress-strain curves for samples prepared with 25% of TBC.

0 4 8 12 16 20

[%]

Fig. 5. The tensile stress-strain curves for samples prepared with 30% of TBC.

0 10 20 30 40 50

Fig. 2. The tensile stress-strain curves for samples prepared with 30% of TEA.

Fig. 3. The tensile stress-strain curves for samples prepared with 35% of TEA.

 12.5TEA30 6.25TEA30 TEA30

 12.5TEA35B 6.25TEA35 TEA35

Fig. 2. The tensile stress-strain curves for samples prepared with 30% of TEA.

0

0

5

10

15

[MPa]

20

25

5

10

15

[MPa]

20

25

30

0 5 10 15 20 25 30 35 40 45 50

[%]

Fig. 3. The tensile stress-strain curves for samples prepared with 35% of TEA.

0 10 20 30 40 50 60

Fig. 4. The tensile stress-strain curves for samples prepared with 25% of TBC.

Fig. 5. The tensile stress-strain curves for samples prepared with 30% of TBC.

The Effect of Concentration and Type of Plasticizer

0

0

2

4

6

8

[MPa]

10

12

14

2

4

6

8

[MPa]

10

12

14

16

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 155

 12.5TEC30 6.25TEC30 TEC30

 12.5TEC35 6.25TEC35 TEC35

Fig. 8. The tensile stress-strain curves for samples prepared with 30% of TEC.

0 5 10 15 20 25 30

[%]

Fig. 9. The tensile stress-strain curves for samples prepared with 35% of TEC.

0 5 10 15 20 25 30 35

Fig. 6. The tensile stress-strain curves for samples prepared with 35% of TBC.

Fig. 7. The tensile stress-strain curves for samples prepared with 25% of TEC.

 12.5TBC35 6.25TBC35 TBC35

 12.5TEC25 6.25TEC25 TEC25

Fig. 6. The tensile stress-strain curves for samples prepared with 35% of TBC.

0

0

5

10

15

[MPa]

20

25

2

4

6

8

10

[MPa]

12

14

16

18

0 10 20 30 40 50 60

[%]

Fig. 7. The tensile stress-strain curves for samples prepared with 25% of TEC.

0 2 4 6 8 10 12

Fig. 8. The tensile stress-strain curves for samples prepared with 30% of TEC.

Fig. 9. The tensile stress-strain curves for samples prepared with 35% of TEC.

The Effect of Concentration and Type of Plasticizer

0

0

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[MPa]

20

25

5

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[MPa]

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25

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 157

 12.5DEP35 6.25DEP35 DEP35

 12.5DBP25 6.25DBP25 DBP25

Fig. 12. The tensile stress-strain curves for samples prepared with 35% of DEP.

0 5 10 15 20

[%]

Fig. 13. The tensile stress-strain curves for samples prepared with 25% of DBP.

0 5 10 15 20 25

Fig. 10. The tensile stress-strain curves for samples prepared with 25% of DEP.

Fig. 11. The tensile stress-strain curves for samples prepared with 30% of DEP.

 12.5DEP25 6.25DEP25 DEP25

> 12.5DEP30 6.25DEP30 DEP30

Fig. 10. The tensile stress-strain curves for samples prepared with 25% of DEP.

0

0

5

10

15

[MPa]

20

25

2

4

6

8

10

MPa]

12

14

16

18

01234567

[%]

Fig. 11. The tensile stress-strain curves for samples prepared with 30% of DEP.

0 2 4 6 8 10 12 14 16 18

Fig. 12. The tensile stress-strain curves for samples prepared with 35% of DEP.

Fig. 13. The tensile stress-strain curves for samples prepared with 25% of DBP.

The Effect of Concentration and Type of Plasticizer

0

0

5

10

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20

MPa]

25

30

35

5

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MPa]

25

30

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 159

 12.5DOP25 6.25DOP25 DOP25

 12.5DOP30 6.25DOP30 DOP30

Fig. 16. The tensile stress-strain curves for samples prepared with 25% of DOP.

0 10 20 30

[%]

Fig. 17. The tensile stress-strain curves for samples prepared with 30% of DOP.

0 10 20 30 40 50 60

Fig. 14. The tensile stress-strain curves for samples prepared with 30% of DBP.

Fig. 15. The tensile stress-strain curves for samples prepared with 35% of DBP.

 12.5DBP30 6.25DBP30 DBP30

 12.5DBP35 6.25DBP35 DBP35

Fig. 14. The tensile stress-strain curves for samples prepared with 30% of DBP.

0

0

5

10

MPa]

15

20

5

10

15

[MPa]

20

25

30

0 10 20 30 40

[%]

Fig. 15. The tensile stress-strain curves for samples prepared with 35% of DBP.

0 10 20 30 40 50

Fig. 16. The tensile stress-strain curves for samples prepared with 25% of DOP.

Fig. 17. The tensile stress-strain curves for samples prepared with 30% of DOP.

The Effect of Concentration and Type of Plasticizer

strength and satisfactory elongation at break.

1998, C6, p. 75-90.

118, p. 3499-3508.

Science 2004, 29, p. 1223-1248.

films and coatings Sothornvit R., Krochta J. M..

Polymer Science 2006, vol. 102, p. 1366-1373.

VCH GmbH&Co. KGaA, Weinheim 2003.

[10] Wypych G. editor, Handbook of Plasticizers, ChemTec Publishing 2004.

Verlag, Munich 2001, chapter 4.2.2. Plasticization, p. 112-116.

p. 402-411.

254-263.

properties.

**7. References** 

on the Mechanical Properties of Cellulose Acetate Butyrate Organic-Inorganic Hybrids 161

most effective to enhance the mechanical properties of CAB and organic-inorganic hybrids, with the highest tensile strength of 31.1 MPa for sample prepared from 87.5/12.5 polymer/TEOS formulation (12.5DOP30). Among citrate plasticizers used in this work, TBC, as well as TEA at 30% concentration were the most effective to improve mechanical

As a final conclusion it can be stated that environmentally friendly citrate plasticizers can substitute phthalates in organic-inorganic CAB hybrids formulations. TBC and TEA can be used as valuable alternatives to DOP, producing materials displaying high values of tensile

[1] Ajayan P. M., Schadler L. S., Braun P. V., Nanocomposite Science and Technology,

[2] Kickelbick G. (Edit.), Hybrid Materials. Synthesis, Characterization, and Applications,

[3] Yano S., Iwata K., Kurita K., Physical properties and structure of organic-inorganic

[4] Kosaka P. M., Kawano Y., Petri H. M., Fantini M. C. A., Petri D. F. S., Structure and

[5] Benaniba M. T., Massardier-Nageotte V., Evaluation Effects of Biobased Plasticizer

[6] Rahman M., Brazel Ch. S., The plasticizer market: an assessment of traditional

[7] Vieira M. G. A., da Silva M. A., dos Santos L. O., Beppu M. M., Natural-based

[8] Han J. H. editor, Innovations in food packaging, Elsevier 2005, in Plasticizers in edible

[9] Gil N., Saska M., Negulescu I., Evaluation of the effects of biobased plasticizers on the

[11] Elias H. G., An introduction to plastics, Second, completely revised edition, WILEY-

[12] Ehrenstein G. W., Polymeric materials: structure, properties, applications, Carl Hanser

hybrid materials produced by sol-gel process, Materials Science and Engineering

Properties of Composites of Polyethylene or Maleated Polyethylene and Cellulose or Cellulose Esters, Journal of Applied Polymer Science 2007, Vol. 103,

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plasticizers and research trends to meet new challenges, Progress in Polymer

plasticizers and biopolymer films: A review, European Polymer Journal 2011, 47, p.

thermal and mechanical properties of poly(vinyl chloride), Journal of Applied

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2003.

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2007.

Fig. 18. The tensile stress-strain curves for samples prepared with 35% of DOP.

#### **6. Conclusions**

Taking into consideration obtained results we can conclude that type and amount of applied plasticizer as well as incorporation of inorganic phase into CAB matrix affected mechanical properties of the examined samples. Changing the type and concentration of the plasticizer, and amount of inorganic phase can modify the strength and extensibility of the materials. The higher the amount of incorporated silica, the harder and more brittle the material, however exhibiting good flexibility at 30 and 35% plasticizer concentration. All of the plasticizers investigated, excluding TEC, caused an antiplasticization effect at concentration 30% resulting in an increase in tensile strength, in comparison with the values at 25%. At higher concentration of plasticizers (35%) the additives caused plasticization reflected as a decreases in tensile strength and an increase in elongation at break values. Regarding the influence of inorganic phase incorporated into polymer matrix, the tensile strength was substantially improved, as compared with neat CAB, regardless of the plasticizer type.

Among all plasticizers, DEP was found to be the least efficient for CAB, as well as for organic-inorganic hybrids. Low plasticization efficiency showed also TEC. All samples prepared with DEP and TEC showed the noticeable low values of tensile strength as well as poor flexibility, as compared to the same formulations with other plasticizers used in this study. DOP, TBC and TEA were the most efficient plasticizers for CAB and organicinorganic CAB hybrids. The best formulations in terms of mechanical properties were those containing 30% of above mentioned plasticizers. DOP at 30% concentration was the most effective to enhance the mechanical properties of CAB and organic-inorganic hybrids, with the highest tensile strength of 31.1 MPa for sample prepared from 87.5/12.5 polymer/TEOS formulation (12.5DOP30). Among citrate plasticizers used in this work, TBC, as well as TEA at 30% concentration were the most effective to improve mechanical properties.

As a final conclusion it can be stated that environmentally friendly citrate plasticizers can substitute phthalates in organic-inorganic CAB hybrids formulations. TBC and TEA can be used as valuable alternatives to DOP, producing materials displaying high values of tensile strength and satisfactory elongation at break.
