PBAT/PLA/Calcium Carbonate Composite

PBAT/PLA/Calcium Carbonate Composite

PBAT/PLA films and PBAT/PLA/CaCO3 composite films were prepared by melt blending and blow molding, and the effects of CaCO3 on the thermal stability, mechanical properties and rheological properties of PBAT/PLA blends were investigated.

01. Specimen Preparation

The PBAT, PLA and CaCO3 samples were first dried in an electric blast drying oven at 70 °C for 48 h. Then PBAT, PLA, compatibilizer polystyrene maleic anhydride copolymer and CaCO3 were mixed uniformly according to the proportions in Table 1, placed in a co-rotating twin-screw extruder for melt blending, the screw speed is 80 r/min, the temperature distribution from the feeding section to the head is 150~175℃, water-cooled pelletizing and drying, the dried pellets are blown with a small film blowing machine, the winding speed is 2.8 m/min, and the film thickness is 0.04 mm. The three samples were marked as PBAT, PBAT/PLA and PBAT/PLA/CaCO3, respectively. 15 parts of PLA and 85 parts of PBAT are selected. If too much PLA is added, it will affect the elongation at break, which is not suitable for the production process of film bags. However, if too little PLA is added, there is no good strengthening effect, so the author chooses to add 15 parts of PLA.

02. Thermal stability analysis of PBAT/PLA/CaCO3 composites

Figure 1 shows the TG curves of PBAT, PLA, PBAT/PLA and PBAT/PLA/CaCO3. PBAT, PLA, and PBAT/PLA/CaCO3 all left carbon residues, indicating the presence of additives and stabilizers in these commercial polymers. In the PBAT/PLA/CaCO3 added with CaCO3, the carbon residue rate reaches 19.2%, which is the residue of CaCO3. Generally, the thermal stability of composite materials is considered as T10% at the temperature at which 10% of the material decomposes. The T10% of PBAT/PLA obtained by the blending of PBAT and PLA was 329.47°C, while the T10% of PBAT/PLA/CaCO3 reached 341.88°C after adding CaCO3. It can be seen that the addition of CaCO3 greatly improves the thermal stability of PBAT/PLA blends, indicating that the addition of CaCO3 can further increase the compatibility of the two.

03. DSC analysis of PBAT/PLA/CaCO3 composites

Figure 2 is the DSC cooling curves for PBAT, PLA, PBAT/PLA and PBAT/PLA/CaCO3. Table 2 is the relevant parameters of its cooling crystallization process at 5°C/min. It can be seen from Figure 2 and Table 2 that both the crystallization temperature and the melting temperature shifted to high temperature after adding PLA to PBAT. Compared with the PBAT/PLA system, the Tc and Tm of the composite membrane materials after adding CaCO3 were significantly increased, which was consistent with the previous TG analysis. The addition of CaCO3 improved the thermal stability of the PBAT/PLA blends. After adding CaCO3, the crystallinity of PBAT/PLA was significantly reduced, which may be because the addition of CaCO3 hindered the movement of molecular chains, resulting in a weakening of the crystallization ability.

04. Mechanical properties of PBAT/PLA/CaCO3 composites

Table 3 lists the mechanical properties of PBAT, PBAT/PLA and PBAT/PLA/CaCO3 composites. It was tested in composite blow molding as a 0.04 mm film. It can be seen from Table 3 that after adding a certain amount of PLA to PBAT, the transverse and longitudinal tensile strengths of the PBAT/PLA film are improved, and the high-strength characteristics of PLA are introduced into the PBAT/PLA blend material. By adding CaCO3 to the PBAT/PLA blend, the transverse and longitudinal tensile strengths of the film were further improved, reaching 24.35 MPa and 28.7 MPa, respectively. This shows that the addition of CaCO3 improves the bonding strength of the two-phase interface between PBAT and PLA. At the same time, the isotropy of PBAT/PLA blends can be improved to varying degrees after the addition of CaCO3, and the tear resistance can be significantly improved.

After measurement, PBAT has good transverse and longitudinal fracture nominal strains, which are 449.3% and 365.3%, respectively, while the two fracture nominal strains of PBAT/PLA after adding PLA have decreased. It can be seen that the longitudinal tensile strength of PBAT and PBAT/PLA is higher than the transverse tensile strength, which is mainly because the PBAT and PBAT/PLA films undergo oriented crystallization in the longitudinal direction during the blowing and winding process, and the crystallinity in the longitudinal direction is higher than that in the transverse direction. The nominal strain at transverse fracture is further reduced after the addition of CaCO3, which is due to the high rigidity of CaCO3 which reduces the original ductility of PBAT/PLA and at the same time, the mobility of its macromolecular chains is reduced, resulting in a decrease in the nominal strain at transverse fracture of the PBAT/PLA/CaCO3 composites. On the other hand, after adding CaCO3, the nominal longitudinal fracture strain of PBAT/PLA blends increased, indicating that the addition of CaCO3 destroyed the crystallinity of PBAT/PLA to a certain extent, which was consistent with the DSC characterization. In terms of hardness, the hardness (HD) of PBAT/PLA blends after adding PLA can reach 44, and the hardness (HD) of PBAT/PLA/CaCO3 composites adding CaCO3 can reach 51, indicating that the addition of CaCO3 improves the hardness of PBAT/PLA blends.

05. Rheological behavior analysis of PBAT/PLA/CaCO3 composites

Figure 3 is the curve of the complex viscosity (η*) of PBAT and PBAT/PLA, PBAT/PLA/CaCO3 composites as a function of frequency. It can be seen from Figure 3 that with the increase of frequency, the η* of PBAT, PBAT/PLA and PBAT/PLA/CaCO3 composites all decrease gradually, showing obvious shear thinning characteristics. This is because with the increase of the external shear force, the entanglement ability of molecular chains in the composite material is weakened, and there is a good fluidity, which leads to the decrease of its η*. After the addition of CaCO3, the η* of the PBAT/PLA/CaCO3 system increases significantly, and the shear thinning property is stronger, which is because the addition of CaCO3 can improve the two-phase compatibility of PBAT/PLA composites.

In the dynamic rheological test of polymer melt, not only can it show reversible elastic deformation, usually the storage modulus (G') is used to characterize the elasticity of the material, but also irreversible viscous flow deformations of polymers can be exhibited. The loss modulus (G″) is usually used to characterize the viscosity of materials.

图4是PBAT与PBAT/PLA，PBAT/PLA/CaCO3两种复合材料的G'和G″随频率的变化曲线图。

Fig. 4 is a graph showing the variation of G' and G" with frequency of PBAT, PBAT/PLA, and PBAT/PLA/CaCO3 composites.

It can be seen from Figure 4 that the G' of pure PBAT and PBAT/PLA, PBAT/PLA/CaCO3 composites all increase with the increase of frequency. In the low frequency range, the G' value of the PBAT/PLA composite is significantly higher than that of pure PBAT. This is due to the interaction between PLA and PBAT matrix after adding PLA, and the degree of entanglement between molecular chains also increases accordingly. It is difficult to destroy this structure under a small force, and the G' of the material increases significantly. After adding CaCO3, because it is evenly dispersed in the matrix, it greatly increases the molecular chain motion resistance of the matrix, and at the same time CaCO3 has a certain compatibilization effect between PBAT and PLA matrix, so the G' value keeps increasing. It can be seen from Figure 4 that the G' of the PBAT/PLA/CaCO3 composite is significantly higher than that of PBAT/PLA in the entire frequency range. At the same time, the G″ also increases significantly after adding CaCO3, which is also due to the compatibilizing effect of CaCO3, which increases the internal friction of the molecular chain during the movement, and also increases the viscous dissipation of the molecular chain movement.

06. Conclusion

(1) The characterization by TG and DSC shows that the addition of CaCO3 greatly increases the thermal stability of PBAT/PLA composites, while reducing the crystallinity of PBAT/PLA composites.

(2) The addition of CaCO3 greatly improved the mechanical properties of the PBAT/PLA composite film. The transverse and longitudinal tensile strengths increased from 21.06 MPa and 24.3 MPa to 24.35 MPa and 28.7 MPa, respectively, and the hardness (HD) reached 51. It shows that CaCO3 has a significant strengthening effect on PBAT/PLA composites.

(3) In the rheological test, the addition of CaCO3 increases the complex viscosity, storage modulus and loss modulus of PBAT/PLA, which further proves that CaCO3 improves the bonding strength of the two-phase interface.

Nanjing Haisi Extrusion supply twin screw extrusion line for PBAT/PLA Caco3 compounding.

Any interest please feel free to contact us!