Study On Polypropylene Foaming By Low Temperature Expandable Graphite

Because expanded polypropylene (EPP) material has high rigidity, good mechanical properties, good heat resistance and chemical stability, as well as good photodegradability and many other advantages, it is a very competitive rival in many industrial applications and has a very bright future. It is interesting to study these foam materials.Low-temperature expandable graphite (LTEG) was prepared in this paper; and then used as a blowing agent in the polypropylene foaming.The LTEG was prepared by using the co-oxidation and intercalation of a variety of oxidants. The effects of the amount of oxidants, intercalation agent concentration and reaction time on the expansion volume of the products were discussed. The structure of the expandable and expanded graphite was characterized and analyzed through infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG) and so on. Research results showed that, the most significant effect of the level of the oxidants and intercalation agents on the expansion volume of EG was the amount of perchloric acid, then sodium bromide, chromium trioxide, potassium permanganate, and ferric chloride in sequential order. The reaction was preferably conducted; at room temperature for 40 minutes, and with the mass ratio of graphite, perchloric acid, sodium bromide, potassium permanganate, chromium trioxide, and ferric chloride by 1:4.0:0.15:0.15 0.13:0.03. The expansion volume of EG product got under the condition can reach as high as 201mL/g at 220℃. FTIR and XRD of the product proved that intercalation agents had been successfully intercalated into the graphite layers. The oxidational intercalation proceeded in the order of oxidation, insertion, and the change of the structure of graphite intercalation sequently.In the study of expandable polypropylene with LTEG as a blowing agent, the effect of the amount of LTEG, foaming temperature and foaming time on the PP foaming process were investigated. The cellular morphology was observed by scanning electron microscopy (SEM), thereafter the foaming process was analyzed. Research results showed that, the EPP foaming in heating oil should be conducred, for better foaming rate, at 220℃for 9 seconds on EG of 17 phr. The density of obtained foam products can go down to 0.64g/cm3. The study of preparing foam PP material by transferring heat through air (oven heating) showed that the foam expansion ratio of PP increased with the increasing the amount of EG, but excessive amount of EG lead to too big bubbles. Considering both of the expansion ratio of EPP and the foam morphology, the preferable amount of expanded graphite in PP was 15 phr. The bubble morphology investigation by SEM and the TG curve of EPP showed that the foam process occurred by both of the EG self expanding and the gas emitted, and then the cellular PP confirmed after cooling.