Modification and utilization of recycled PP materials

Enhanced modification

The tensile strength of the recycled PP is relatively low. The general product is about 18 to 25 MPa. After being reinforced with short glass fiber (SGF), the tensile strength can reach about 30 to 35 MPa. In order to improve the interfacial properties of fiber and resin, commonly used coupling agents such as KH550, KH560, KH570, etc., the amount of coupling agent is generally 0.2% to 1.5% of the fiber content, it is necessary to test and determine for different situations.

Chlorination of polypropylene

Recycling PP can also be chlorinated like recycled PE, which has a wide range of applications. For example, aPP can be chlorinated to obtain chlorinated aPP (CaPP), which has excellent bonding properties and can be used to bond binders for PE, PVC, Pa, metal, etc., such as packaging composite film, double A binder such as a layer PP film, a PP film-paper, a PP film, or an aluminum foil. In addition, CaPP can also be used as a processing aid for coatings, printing inks and polar resins.

Graft modification of polypropylene

The chemical modification of polypropylene also has copolymerization modification such as grafting and block. The purpose of graft modification of polypropylene is to improve the adhesion or solubilization of polypropylene to metals, polar plastics, and inorganic fillers. The grafting monomers used are generally acrylic acid and its esters, maleic anhydride and its esters, maleimides and the like. The grafting method includes: 1 solution method, adding a peroxide initiator to the solvent for copolymerization; 2 radiation method, grafting under high energy rays; 3 melt mixing method, in the presence of peroxide, in a molten state The mixture is kneaded and grafted, often in a twin-screw extruder. The properties of the graft modified polymer materials are related to the physicochemical properties of the grafts, and also related to the content of the grafts, the length of the graft chains, etc. The basic properties are similar to those of polypropylene, but with polar polymer materials. The compatibility of inorganic materials and rubber can be greatly improved. The crystallinity and melting point of grafted PP decrease with the progress of graft content, and the transparency and low-temperature heat sealability are improved.

Crosslinking modification of recycled polypropylene

The recycled polypropylene can also be cross-linked modified like polyethylene, and the modification mechanism is similar to that of the polyethylene described above.

Catalytic cracking and thermal cracking of polypropylene

Polypropylene is cracked at about 380 ° C for thermal cracking and catalytic cracking. Using a silicon/aluminum powder (SiO 2 /al:03) as a catalyst, the catalyst can be contacted with the gas phase and liquid phase of the cracked product. Studies have shown that by liquid phase contact catalyst method, 69% liquid product can be obtained, with a boiling point of 30-270 ° C, 2 · C6 to n-C1s paraffin oil; gas phase contact catalysis, can obtain 54% (mass fraction) liquid product And the speed of getting the product is much lower. Studies on both catalytic and non-catalytic degradation have shown that the unsaturation of the catalytically degraded liquid product is much higher than that of the non-catalytic degradation, and the cleavage products are also different.

Polypropylene decomposes under the action of a catalyst at around 40013 to produce a series of substances. Studies have shown that advances in catalyst levels can improve liquid yields while reducing the amount of gases and residues; the type of catalyst has little effect on yield and composition. The temperature has an effect on the cracking reaction, the temperature is improved, the liquid forming rate is improved, and the percentage of the residue is lowered, and the gas amount is slightly lowered. The cracking atmosphere has an effect on the cracked product, and cracking in a water vapor atmosphere can improve the liquid formation rate. In addition, the mixing of other waste plastics did not reveal products other than the cracking products of the respective polymers, that is, no interaction such as a synergistic reaction occurred in the cracking reaction. Under medium temperature cracking conditions, the liquid formation rate is about 70%, and the appropriate improvement technique can increase the liquid formation rate to about 85%.