Study On The Improvement Of Recycled Polypropylene Resin Spinnability

Polypropylene (PP) is a kind of cheap general resin with excellent performance such aselectrical insulation, small density, etc. So it is widely used in plastics, fiber, daily necessities,packaging film, industrial products, coatings and other fields. In recent years, with the increasingproduction and consumption of polypropylene products, waste PP materials are also increasing.Generally, waste PP materials contain a certain amount of high density polyethylene (HDPE),since PP and HDPE are very similar in appearance, density, etc., it is difficult to separate. Thisaffects recycled polypropylene (rPP) spinnability, and makes the production of recycledpolypropylene fiber performance fluctuations, unstable. To solve this problem, this study aims to:through the research on composition and spinnability of different contents of HDPE in PP blendedcomposite resin, PP/HDPE composition analysis methods were established and their spinnabilityimprovement schemes were developed. Further, the above findings applied to rPP spinnabilityimprovements. The main contents and the corresponding results were summarized as follows:(1) The structure and thermal performance of five kinds of rPP were tested and analyzed byFTIR-ATR, DSC and TGA. The results showed that five kinds of rPP contained HDPEcomposition. Further use of FTIR-ATR analysis of PP/HDPE blends, it was defined the HDPEcharacteristic absorption peak (720cm-1) peak area and PP characteristic absorption peak (1375cm-1) peak area ratio as the dependent variable, HDPE percentages as independent variables, andthen a standard curve measured the contents of HDPE in rPP were established. The results showedthat the contents of HDPE in Chenshuihei were4.38wt%, Motou(5.25wt%), Gousheng(14.35wt%),Chenshuilv(10.27wt%), Lanse(1.36wt%) respectively. By SEM-EDS, the results showed that eachrPP contained a certain amount of Si, Mg, Al, Ca, Fe, Na, Ti impurities and the contents ofimpurities in the rPP were analyzed by ICP. In addition, GPC was carried out on the rPPmolecular weight distribution, the results showed that the molecular weight of the different rPP was obviously different and the molecular weight of material-Lanse was the biggest.(2) Research on the effects on spinnability when HDPE and PP-g-MAH were introduced intoPP/HDPE blends, the conclusions were: through SEM observation of PP/HDPE composite resin,the results showed that PP and HDPE were completely incompatible. In addition, with the increaseof contents of HDPE, melt flow rate was decreased. And by spinning experiment, it was found thatwhen the contents of HDPE were up to20wt%in PP/HDPE blends, the fiber quality became theworst and the maximum draft ratio was only3.3times. On the mechanical properties, by adding20wt%HDPE of PP/HDPE fiber mechanical strength reached2.0cN/dtex (the lowest).However, the compatibility of PP and HDPE was greatly improved with the introduction ofPP-g-MAH, and the best additive amount of PP-g-MAH was50wt%of the content of HDPE inPP/HDPE blends. In addition, the liquidity of PP/PP-g-MAH/HDPE was also improved. The fiberspinnability and draft ratio were greatly increased, and the maximum draft ratio was3.7times.Finally the fiber performance test results showed that the sonic orientation value (fs) ofPP/PP-g-MAH/HDPE fiber was larger than PP/HDPE fiber. On the mechanical properties, byadding10wt%PP-g-MAH of PP/PP-g-MAH/HDPE fiber mechanical strength reached4.9cN/dtex(the largest).(3) The above research conclusions were applied to improve the spinnability of three rPPwith different impurities contents. Three kinds of rPP: Lanse, Motou, Chenshuilv and theirmodified rPP by adding PP-g-MAH were tested by capillary rheometer. The results showed thatrPP melts were shear thinning fluids. At different shear rate, the apparent viscosity of rPPdecreased as the temperature rose, and the flow of rPP/PP-g-MAH composite resin was higherthan rPP resin. According to apparent viscosity of PP at shear rate1387S-1at250?, the spinningtemperature range of three rPP and rPP/PP-g-MAH composite resin were identified. Finally thefiber performance test results showed that as for the rPP/PP-g-MAH fibers, the sonic orientationdegree and their sound sonic modulus were larger than rPP fibers. And the mechanical strength ofrPP/PP-g-MAH fiber increased0.3~0.4cN/dtex accordingly. However they were not improvedsignificantly. This was due to there were a large number of inorganic impurities in the rPP, whichreduced their spinnability and fiber properties. As for the factory, the inorganic impurities shouldbe strengthened to remove firstly, and then to improve rPP spinnability and fiber performance withthe introduction of compatibilizer.