Results and discussion- Mechanical Properties-Project1

3.1. Mechanical properties

3.1.1. Tensile strength

Table- 1 shows the tensile strength, tensile modulus and elongation at break of PBAT, PBAT bio-nanocomposite hybrids respectively. It is evident that incorporation of nanoclays results in an increase in the tensile modulus of matrix polymer in both transverse and as well as in machine direction respectively. Test results represented in Table-1 summarizes that the young’s modulus of PBAT virgin is 26.20 MPa in transverse direction and 30.17 MPa in machine direction respectively. Incorporation of nanoclays leads to substantial increase in the young’s modulus in both the directions. In case of the nanocomposite prepared using C30B nanoclay an increase of young’s modulus to the tune of 30.59% and 31.99% respectively was observed. This increase in the modulus is probably due to high aspect ratio of the nanoclays that results in strong interaction between PBAT matrix and nanofiller. A similar increase in young’s modulus of PBAT/B109, PBAT/C20A nanocomposite hybrids was also noticed to the tune of 38.88% 46.94%, and 14.50% 7.22% in transverse and machine direction respectively as compared with the virgin matrix. The increase in young’s modulus of virgin PBAT matrix follows the following order PBAT/B109>PBAT/C30B>PBAT/C20A> PBAT/Na⁺MMT.

The nanocomposite hybrid with B109 exhibited optimum performance as compared with the other nanocomposite hybrids. This behavior is probably due to the homogeneous distribution and micro dispersion of nanoclay facilitating separation of tactoids and platelets resulting in partial exfoliation and intercalation accomplished through shear stress during melt compounding. Furthermore, B109, a hectorite layered Mg silicate variant of smectite clay provides more particles per gram as well as smaller platelets thus, creating more surface area exhibiting improved performance characteristics as compared with other organically modified montmorillonites, i,e, C20A and C30B respectively.

In all the cases, the nanocomposite hybrids exhibited higher performance in the machine direction, which is probably due to the uniform alignment and improved interfacial adhesion of the nanoscale reinforcement within the PBAT matrix.

However addition of nanoclays leads to a decrease in tensile strength as well as elongation at break. This decrease can be correlated with the nanoclay content wherein more pronounced effect was observed for PBAT/Na⁺MMT hybrid, which further indicates lower affinity of PBAT matrix with hydrophilic Na⁺MMT.

The tensile properties of blown films derived from maleic anhydride grafted PBAT (MA-g-PBAT) bio-nanocomposite hybrids using various organically modified nanoclays: B109, C30B, C20A at 3wt% is depicted in table-2. It is observed that the grafted samples exhibited improved tensile modulus as compared with the ungrafted bio-nanocomposite hybrids. In case of MA-g-PBAT/C30B, an increase of 44% and 86.32 % of tensile modulus in transverse and machine direction respectively as well as marginal increase in tensile strength from 6.8 to 10.21 MPa in transverse direction and 10.78 to 15.31 MPa in machine direction were observed. This behavior is primarily due to modification of interfacial region between PBAT matrix and C30B organoclay. MA acts as a bridge forming an ester linkage with the –OH group of C30B. Furthermore, an intra molecular hydrogen bond is also formed between the carbonyl group of PBAT and hydroxyl –OH groups of MA.

A similar increase in elongation at break was also observed in both the directions. Nanocomposite hybrids of B109, C20A with MA-g-PBAT also exhibited an increase in the young’s modulus to approximately 84% and 74% in machine direction and 100%, 61% in transverse direction respectively. This is probably due to the formation of inter molecular hydrogen bonding between hydrogenated tallow groups of B109 and C20A and MA-g-PBAT matrix. However, the bio-nanocomposite hybrid prepared using B109 clay exhibited maximum young’s modulus, which can be explained due to similar cause that B109 provides increased clay platelets per surface area of contact with virgin matrix.

The existence of interfacial bonds in grafted nanocomposite hybrids system have already been corroborated using FTIR spectroscopy. In all cases the elongation at break in the transverse direction increased which is presumably assumed because of formation of chemical/physical network between the polyester chains and the organoclays, while restricting the extension of the matrix chains in the machine direction to the same extent .

3.1.2. Tear strength

The tear resistance of PBAT matrix and the bio-nanocomposite hybrids is shown in table 3. The virgin biopolymer exhibits tear strength of 335.3 g/mm. Incorporation of nanoclays results in an increase in the tear resistance of the matrix polymer. Nearly 19% increase in the tear strength of PBAT matrix was observed in PBAT/B109 bio-nanocomposite hybrid, which indicates effective stress transfer from the organically modified nanoclays to the virgin matrix. Furthermore, formation of an intercalated structure also might have contributed to an increase in the tear resistance. PBAT/C30B as well as PBAT/C20A bio-nanocomposite hybrid also exhibited an increase in tear strength of PBAT from 335.3 g/mm to 343.17 g/mm and 283.00 g/mm respectively.

Further, functionalization of PBAT matrix with MA through reactive extrusion results in modification of the interfacial region between PBAT and nanoclays through formation of covalent bonds/hydrogen bonds with suitable chemical/pendent groups. The bio-nanocomposite hybrid of MA-g-PBAT/B109 exhibited a tear resistance of 445.39gm/mm where as MA-g-PBAT/C30B exhibited a tear resistance of 375.05gm/mm respectively. Bio-nanocomposite hybrid prepared using C20A showed marginally high tear resistance as compared with virgin PBAT matrix which is probably due to less affinity of C20A clay, organically modified with methyl dihydrogenated tallow quaternary ammonium salt with the PBAT matrix. Furthermore grafted nanocomposite hybrid MA-g-PBAT/C20A also could not exhibit any appreciable change in the tear resistance.