The pvc brittleness of the pvc profile is basically fully reflected in the physical and mechanical properties of the product.
Its main features are: collapse during cutting, cold explosion and cracking.
There are many reasons for the poor physical and mechanical properties of profile products, mainly in:
First, the formulation and mixing process is unreasonable.
1-excessive filler
In view of the current decline in the price of finished products on the market and the rise in raw material prices, profile manufacturers are reducing costs.
Formal combinations of formulators reduce costs without sacrificing quality; some manufacturers reduce product quality while reducing costs.
Due to the formulation ingredients, the most direct and effective method is to increase the filler. A commonly used filler in U-PVC plastic profiles is calcium carbonate.
Most of the previous formulation systems were filled with calcium to increase rigidity and reduce costs. Due to the irregular shape of the particles and the relatively large particle size and poor compatibility with the pvc resin body, the heavy calcium is very small.
Low, the number of parts increases the color and appearance of the profile.
With the development of technology, ultra-fine and light activated calcium carbonate, even nano-scale calcium carbonate, not only plays a role in increasing rigidity and filling, but also has a modifying effect, but the filling amount is not
Unlimited, the ratio should be controlled.
Some manufacturers now add calcium carbonate to twenty to fifty parts by mass to reduce costs, which greatly reduces the physical and mechanical properties of the profile, leading to the brittleness of the profiles described in this chapter.
Type and number of 2-added impact modifiers
The impact modifier is a high molecular polymer that increases the total energy of the cracking of the polyvinyl chloride under stress.
The main varieties of rigid PVC impact modifiers are MBS (methyl methacrylate, butadiene, styrene terpolymer), ABS (acrylonitrile (A), butadiene (B), benzene). Ethylene (S) terpolymer of three monomers), EVA (ethylene-vinyl acetate copolymer), CPE (chlorinated polyethylene), ACR (acrylate). Among these varieties, EVA (ethylene-vinyl acetate copolymer), CPE (chlorinated polyethylene), ACR (acrylate), and a modification enhancer have a structure which does not contain a double bond and has relatively good weather resistance.
As outdoor building materials, they are mixed with PVC to effectively improve the impact resistance of rigid PVC, subsequent processability, and weather resistance, and improve the welding angle strength within a certain range. In the PVC--CPE blend system, the impact strength increases with the increase of the amount of CPE, showing an S-shaped curve.
When the amount added is less than eight parts by mass, the impact strength of the system is rarely increased; when it is eight to fifteen parts by mass, the amount of addition is increased the most; then the growth rate tends to be mild.
When the amount of CPE is less than eight parts by mass, it is not sufficient to form a network structure; when the amount of CPE is eight to fifteen parts by mass, it is continuously and uniformly dispersed in the blend system to form a network in which phase separation is not separated. Structure to thereby blend.
The impact strength of the system increases the most; when the amount of CPE exceeds 15 parts by mass, continuous and uniform dispersion cannot be formed, but some CPE forms a gel, so we can say that there is no suitable dispersed CPE particles at the interface of the two phases. .
In order to absorb the impact energy, the impact strength tends to increase slowly.
And PVC / ACR mixture
In this system, ACR can significantly improve the impact resistance of the blend. In addition, the "core-shell" particles can be uniformly dispersed in the PVC matrix. PVC is the continuous phase, ACR is the dispersed phase, which is dispersed in the continuous phase of PVC to interact with PVC. PVC acts as a processing aid to promote the plasticization of PVC.
Solid-state gelation, plasticization time is short, and subsequent processing performance is better.
The molding temperature and plasticizing time have little effect on the notched impact strength, and the bending elastic modulus decreases little.
In general, the ACR-modified rigid PVC product is used in an amount of 5 to 7 parts by mass, and has excellent room temperature impact strength or low-temperature impact strength.
Experimental evidence indicates that the impact strength of ACR is 30% higher than that of CPE.
The PVC--ACR blend system should be used as much as possible in the formulation. If the modified amount of CPE is less than eight parts by mass, the profile will become brittle.