In recent years, with the rapid development of calcium carbonate processing technology and the rapid development of calcium carbonate surface treatment technology, it can improve many properties of products while reducing the cost of products, and some properties are unique.
Positive Modification of Calcium Carbonate
1. Environmental benefits of calcium carbonate
(1) Save oil resources
Based on 30% calcium carbonate filling in PE, the annual output of plastic packaging bags is 3 million tons, which can save 900,000 tons of petroleum-based resin and 2.7 million tons of oil.
(2) Giving environmental protection performance
Adding calcium carbonate to the incinerated plastic garbage bags can increase the burning speed and greatly shorten the burning time. The specific reason is that the calcium carbonate in the plastic film expands when it is burned and generates numerous tiny pores, which increases the combustible area in contact with oxygen and promotes the burning speed. For example, for polyethylene plastic film containing 30% calcium carbonate, the burning time is reduced from 12 seconds for pure plastic film to 4 seconds.
The plastic film filled with calcium carbonate, due to the wicking effect of calcium carbonate, can promote more thorough burning and reduce the release of black smoke. It can also use the alkalinity of calcium carbonate in the film to absorb a large amount of dispersed acid gas, reduce the release of toxic smoke, and greatly reduce the probability of acid rain.
2. Universal Modification Efficacy of Calcium Carbonate
(1) Improve the rigidity of composite materials
Calcium carbonate can improve the flexural strength, flexural modulus, hardness, wear resistance and other properties of the composite material. For plastic films, the improvement of the rigidity of the composite material can significantly increase the stiffness of the film, which is beneficial to the flat curling of the film.
(2) Improve the dimensional stability of composite materials
The improvement of dimensional stability is reflected in the reduction of shrinkage, warpage, linear expansion coefficient, creep, and isotropy. Calcium carbonate filling can significantly improve dimensional stability.
(3) Improve the heat resistance of composite materials
Calcium carbonate can improve the thermal stability of composites because calcium carbonate can absorb substances that promote decomposition. For example, the thermal stability of PBAT/calcium carbonate composite is significantly higher than that of pure PBAT. Another example, especially adding light calcium carbonate to PVC products, can absorb the hydrogen chloride generated by decomposition, and greatly improve the thermal stability of PVC processing.
(4) Improve the tear resistance of the film
General plastic films have the shortcomings of high longitudinal strength and low transverse strength, especially PBS, PLA, PHA aliphatic polyester films are more obvious. After adding calcium carbonate, the degree of isotropy of the composite material can be improved, and the tear resistance performance can be obviously improved.
3. Special modification properties of calcium carbonate
(1) Effects on tensile and impact properties
Not all calcium carbonate can improve the tensile strength and impact strength of plastic films, which are affected by calcium carbonate particle size and surface treatment.
The effect of particle size: The particle size of calcium carbonate is different, and the modification effect on plastic is different, as shown in Table 1. Generally, the particle size is below 1000 mesh, which is mainly used for incremental modification; the particle size is 1000~3000 mesh, and the addition amount is below 10%, which has a certain modification effect; the particle size is above 5000 mesh, which belongs to functional calcium carbonate, with The obvious modification effect can improve the tensile strength and impact strength. Although nano-scale calcium carbonate has a finer particle size, it can only achieve the same modification effect as 8000 mesh calcium carbonate because it is difficult to disperse at present.
Negative Modification of Calcium Carbonate
1. Increase the density of composite materials
When calcium carbonate is added to the resin, the density of the composite increases rapidly, so that for products sold by number, length or area, the increased density can offset some of the cost advantage. Of course, the degree of weight gain of different varieties of calcium carbonate is slightly different, and the specific density order is light calcium carbonate < large calcite calcium carbonate < marble calcium carbonate < dolomite calcium carbonate < small calcite calcium carbonate.
How to reduce the density of calcium carbonate composite plastics?
(1) Product stretching and weight reduction
Stretching can create deformation voids between the plastic and calcium carbonate, which can slightly reduce the density of the product. For example, the density of the stretched 30% calcium carbonate filled polyethylene film is 1.1g/cm3, while the unstretched 30% The density of calcium carbonate filled polyethylene film is 1.2g/m3. Stretch-formed plastic products such as flat yarn, blown film, packing tape, tear film, etc.
(2) Micro-foaming weight reduction of products
Micro-foaming is carried out by using the moisture absorbed by the filler, the density is greatly reduced, and the performance is basically not reduced. For example, the 50% lightweight calcium carbonate composite we produce can achieve a minimum density of 0.7 when used in the production of thin films, which is as much as 45% lighter.
(3) Hollow filling to reduce weight
Using simple and low-cost inorganic powder hollowing technology, calcium carbonate can be easily made into hollow products, and its density can be greatly reduced. The lowest density of calcium carbonate hollow products can be reduced to about 0.7g/cm3.
2. Reduce the gloss of composites
The effect on the surface gloss of composite products is related to the processing method and variety of calcium carbonate. The order of the gloss of specific composite materials is wet process > dry process (light calcium carbonate > large calcite calcium carbonate > marble calcium carbonate > small calcite calcium carbonate > dolomite calcium carbonate).
3. Reduced transparency of composites
The refractive index of calcium carbonate is very different from that of commonly used resins such as polyethylene and polypropylene, so the filling of calcium carbonate of regular size will affect the transparency of the film. Affect the transparency of composite products.
4. Reduced elongation at break of composites
The high rigidity of calcium carbonate will reduce the original ductility of the composite material and reduce the mobility of the macromolecular chain, resulting in a decrease in the elongation at break of the product.
5. Decreases tensile and impact strength of composites in most cases
Too large particles of calcium carbonate or poor surface treatment of calcium carbonate will lead to the decrease of tensile strength and impact strength of composite materials, especially the decrease of tensile strength is the most obvious.
6. Increased stress whitening
The resin is filled with a large amount of calcium carbonate, because the stretching of the product will produce a large number of voids and silver streaks, which will further strengthen the inherent stress whitening phenomenon of the resin.
7. Accelerates product aging
All inorganic powder materials accelerate the aging of composite materials, and calcium carbonate is no exception.
8. Reduce the strength of the connection between materials
For the film, reduce the heat seal strength of the film, and for the pipe, reduce the welding strength of the pipe.