What properties of polyethylene are improved by calcium carbonate?

Calcium carbonate (CaCO₃) serves as a high-quality filler and white pigment, characterized by high whiteness, good biocompatibility, and being non-toxic and odorless. It is widely used in fields such as rubber, plastics, papermaking, coatings, inks, pharmaceuticals, and cosmetics. Modified calcium carbonate has lower costs and excellent thermal properties, making it an outstanding inorganic filler in plastic manufacturing.

Modified heavy calcium carbonate₃
      Modified heavy calcium carbonate particles play a role in heterogeneous nucleation within the system, enhancing the crystallinity of the material, increasing the crystallization rate, compressing the crystallization time, refining the grain size, improving material rigidity, and enhancing impact strength. Researchers conducted modification experiments on high-density polyethylene films using titanate-activated heavy calcium carbonate. The study found that in the HDPE/POE/CaCO3 system, when the mass fractions of polyolefin elastomer (POE) and heavy calcium carbonate are 10% and 5% respectively, the unit drop weight impact strength of the film increases by 95.6% compared to pure HDPE, while the tensile strength remains unchanged. However, excessive use of calcium carbonate reduces the dispersion of the composite material, leading to increased drawbacks from agglomeration and decreased impact strength.

Nano calcium carbonate filler
      Nano calcium carbonate particles have a small particle size and a large specific surface area, providing a larger contact area with the matrix. They can act as stress concentration points within polyethylene matrices. When nano calcium carbonate fills polyolefin products subjected to external forces, shear stress around the particles is transferred, allowing the connected matrix to yield locally and absorb more energy, thereby enhancing toughness. At the same time, it can hinder or blunt crack propagation when polymers are impacted by external forces. However, when the addition of nano calcium carbonate exceeds a certain amount, agglomeration occurs due to high surface energy, leading to decreased dispersion and increased interfacial defects, which reduces the toughness of polyethylene products filled with nano calcium carbonate. A small amount of nano calcium carbonate added to high-density polyethylene can also act as a nucleating agent to promote polyethylene crystallization, facilitating tight and orderly molecular chain arrangement and enhancing intermolecular interactions beneficial for increasing tensile strength; it can also improve polyethylene's crystallinity and heat resistance significantly raising the Vicat softening temperature of the material. However, excessive nano particles hinder molecular chain movement and can reduce tensile strength.

Research status
      Using different morphologies of calcium carbonate (CaCO₃) as fillers with low-density linear polyethylene (LLDPE) and high-density polyethylene (HDPE) as matrices, LLDPE/HDPE/CaCO₃composites were prepared using a twin-screw assisted secondary mixing injection molding process. The oil absorption value, whiteness, activation degree, etc., of different morphologies of calcium carbonate fillers were characterized. The cross-sectional morphology and thermodynamic properties of LLDPE/HDPE/CaCO₃composites were analyzed.

Results
       (1) Using a method of pre-mixing once and processing twice during mixing allows for more uniform dispersion of calcium carbonate in the resin matrix. The resulting LLDPE/HDPE/CaCO₃composites exhibit better thermal stability and mechanical performance.

(2) The inclusion of calcium carbonate effectively enhances the thermal decomposition temperature of LLDPE/HDPE/CaCO₃composites, providing corresponding thermal shielding properties; the decomposition temperature of LLDPE/HDPE resin matrix increases by about 20°C, improving material thermal stability.

(3)The five different morphologies of filled calcium carbonate significantly improve the mechanical properties of LLDPE/HDPE composites. Ultrafine active heavy calcium disperses uniformly in LLDPE/HDPE matrices with complementary particle sizes; its impact strength is 4.15 times that of LLDPE/HDPE; rod-shaped active light calcium also disperses uniformly in the resin matrix with a bending strength twice that of pure LLDPE/HDPE composites. Polyethylene (abbreviated as PE) is a thermoplastic resin obtained from polymerizing ethylene with a chemical formula of (C2H4)n. In industry, it also includes copolymers of ethylene with small amounts of α-olefins. Pure polyethylene is milky white, non-toxic, odorless, tasteless, and has a wax-like feel. Polyethylene has good chemical stability and can resist most acid-base corrosion but has poor tolerance to oxidizing acids. It is insoluble in common solvents at room temperature with low water absorption and excellent electrical insulation properties. Due to its outstanding physical and chemical properties, polyethylene is one of the most widely used plastics globally. It can be used to produce films, packaging materials, pipes for transporting acids and various solvents, container linings as well as insulation materials for wires and cables; it is also used in daily necessities and construction materials as well as high-frequency insulation materials for devices like televisions and radars. Additionally, nano calcium carbonate has extensive applications in agriculture such as agricultural films and irrigation pipes.

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