Effect of calcium carbonate content on the properties of PBAT
As a thermoplastic biodegradable material, PBAT is formed by the polycondensation of butanol adipate (PBA) and butylene terephthalate (PBT). It has good ductility, processability, safety, and biodegradability. Advantages have become a hot topic in recent years.
However, the crystallinity of PBAT is high, the viscosity during processing is high, and the price of PBAT is high, which limits the popularization and use of PBAT.
Calcium carbonate has the characteristics of low cost and is helpful for plastic processing. Therefore, adding calcium carbonate to PBAT can improve its processing performance and reduce costs. However, different contents of calcium carbonate have different effects on the performance of PBAT, as follows:
1. The effect of calcium carbonate content on the density of PBAT
Figure 1 shows the effect of calcium carbonate content on the density of PBAT. It can be seen from the figure that the density of pure PBAT is 1.21 g/cm3. With the increase of calcium carbonate content, the density of PBAT increases. When the content of calcium carbonate masterbatch is 10%, the density is 1.26 g/cm3, the difference between the two is 0.05, and the density is improved. When the content of calcium carbonate masterbatch is 40%, the density is 1.44 g/cm3, and the increase rate increases. The density of calcium carbonate is 2.75 g/cm3, and the density of calcium carbonate is greater than that of PBAT, so the density of PBAT/calcium carbonate composite increases with the increase of calcium carbonate.
2. The effect of calcium carbonate content on the tensile strength of PBAT
Figure 2 shows the effect of calcium carbonate content on the tensile strength of PBAT. It can be seen from the figure that with the increase of calcium carbonate content, the tensile strength of PBAT decreases. When the calcium carbonate content is 10 %, the tensile strength of PBAT drops to 14.45 MPa, which is 6.73 MPa and 31.78 % lower than that of pure PBAT, which is 21.18 MPa. It shows that with the continuous addition of calcium carbonate particles, the continuity of the molecular structure of PBAT is broken, and the continuity of calcium carbonate particles is poor, which reduces the stress of the PBAT/calcium carbonate composite, thereby reducing the tensile strength.
In addition, the poor interfacial bonding strength of PBAT and calcium carbonate is also one of the important reasons for the decrease of the tensile strength of PBAT. It is necessary to carry out research on strengthening the interfacial bonding ability of PBAT and calcium carbonate in the later stage.
3. Effect of calcium carbonate content on elongation at break of PBAT
The elongation at break refers to the ratio of the elongation after tensile fracture to the original length before stretching when the material is stretched to break. The elongation at break of PBAT showed a decreasing trend as a whole with the increase of calcium carbonate content. Calcium carbonate content between 30 % and 40 % decreased significantly faster than calcium carbonate content between 0 and 30 %.
Due to the presence of ester groups in the molecular structure of PBAT, its own flexibility is better. As an inorganic material, calcium carbonate has a small molecular weight and almost no deformation ability. In addition, the addition of calcium carbonate particles into PBAT reduces the mobility and force transfer of macromolecular chains, resulting in a decrease in the elongation at break of the PBAT/calcium carbonate composite.
4. The effect of calcium carbonate content on the impact strength of PBAT
Figure 3 shows the effect of calcium carbonate content on the impact strength of PBAT. The study found that the impact strength of PBAT increased with the increase of calcium carbonate content. The toughness of pure PBAT spline is 39.36 KJ/m2, the impact strength is 42.38 KJ/cm2 when the content of calcium carbonate masterbatch is 10%, and the impact strength reaches the highest 57.67 KJ/m2 when the content of calcium carbonate masterbatch is 40%.
When the calcium carbonate content is low, the impacted splines will deform at the notch. When the content increases, cracks and silver streaks will appear in the notch of the punched sample, indicating that the calcium carbonate particles are dispersed in the PBAT/calcium carbonate composite. Under the action of external force, concentrated stress will be generated, and the craze will absorb the force, thereby improving the impact performance of the composite material.
In addition, calcium carbonate, as an inorganic rigid particle, has higher hardness and rigidity than PBAT. When PBAT/calcium carbonate is damaged by impact, the presence of calcium carbonate rigid particles will make the composite material produce higher performance compared to the PBAT flexible matrix. Reaction force, thereby improving the impact strength test results of PBAT.
