The treatment was conducted at Borica lab with 1kg batch glassware
Dosage of titanate coupling agent: 1wt% based on CaCO3 weight

Procedure
1. Preheat CaCO3 at 100C for 1 hr
2. Dilute titanate with hexane at 1:25 ratio
3. Add titanate solution into CaCO3, stirring at around 60~70C
4. Strip off hexane then put dried CaCO3 at oven at 110C for 2hrs.

Loading of CaCO3: 50% in PP for all test groups.
Temperature profile of twin extruder: 210C for all sections
Screw rotation speed: 200~300 rpm with 400~600g/hr feeding rate
PP/CaCO3 was extruded twice to ensure the uniformity of the composite
The sample was then pelletized and injection molded into test specimen.

Table 1. Performance of titanate couplings and stearic acid

Coupling agent	Pretreatment	Dosage (wt% on CaCO3)	Tensile strength (MPa)	Stress at break (MPa)	Elongation at break (%)
N/A	N/A	N/A	21.14	17.39	163.69
Stearic acid	Yes	2%	24.13	21.54	305.93
CP-326	Yes	1%	23.89	22.07	543.01
CP-317	Yes	1%	23.89	22.07	543.01
CP-219	Yes	1%	22.66	21.43	497.08

Surface treatment of CaCO3 shows positive effect on mechanical properties of the composite. Elongation at break was improved significantly for all 5 groups without sacrificing the tensile strength or stress at break. Elongation for titanate treated composite was higher than stearic acid treated composite with lower dosage. One possible explanation is that titanate is a bulkier molecule than stearic acid. When CaCO3 is coated by titanate, the bulkier structure may exert more distance between CaCO3 particles, giving better dispersion in the polypropylene. Good dispersion means less CaCO3 agglomeration hence less voids are created in the composite. Another reason might be that the 3 long carbon chains attached on Ti provide higher extent of entanglement with polypropylene polymer chain than stearic acid, which contains only 1 carbon chain.