Studies Of The Modification Of Recycled Low Density Polyethylene Materials

Polyethylene is the largest output, the most widely used and the largest ofconsumption variety in the plastic industy. With the expanding of polythelene’sconsumption market and the growing diversity of consumer products, thequantity of the litter is also increasing. By modified regeneration to producehigh value-added materials is the main way to recover polyethylene wasteplastics. It’s also the emphasis and focus of recycling research. This researchwas supported by the National Science and Technology Support Program ofChina (2007BAE42B04). Recycled low density polyethylene was used as themain raw materials. Different types and proportions virgin materials, plasticizers,lubricants were blended to modified recycled basic research. Infrared, electronmicroscopy and mechanical properties and oeher analytical methods were used.The practical performance and processing performance were studied betweenrecycled materials and virgin materials. Finally, by orthogonal experiment, thebest formula of modified recycled materials was studied. The results wereconcluded as follows:(1) The density, melt flow rate, element, molecular weight, group, thermalperformance, rotation of the rheological properties, torque rheological properties,mechanical properties and other aspects of recycled materials were measured andanalyzed. From IR spectroscopy and DSC analysis, the main component of therecycled material can be seen. LDPE and LLDPE were the main component ofthe recycled materials. Some part of the group is oxidized. By high temperaturegel permeation chromatography, it is can be found that the weight-averagemolecular weight of recycled materials (207,200) is larger than the weight ofvirgin LDPE (171,579). The molecular weight distribution index of recycledmaterials is5.2, which is less than6.7of virgin LDPE. The new materials hasmore low molecular weight fraction than the recycled materials. However. Therecycled materials has more high molecular weight fraction than virgin materials.The mechanical analysis shows that the tensile strength of recycled materials(22.423MPa) is higher than virgin LDPE (14.740MPa). However, the elongationat break (172.39%) of recycled materials is lower than virgin LDPE______________________________________________________________________________________________ (200.06%).The flexural strength of recycled materials (5.5MPa) is lower thanvirgin LDPE (6.2MPa). From rotating rheological and torque rheological test, wecan found that the processability of recycled materials is bad compared withvirgin LDPE. The equilibrium torque of recycled materials is13.3N.m, howerer,the equilibrium torque of virgin LDPE is4.6N.m.(2) The virgin polyolefin can influence the mechanical properties ofrecycled materials. When the content of virgin materials are10%, the influencesof the four virgin materials to tensile strength are small. With the increasing ofthe content of virgin materials, the influence is increasing, except forRLDPE/HDPE, which the largest rate of change is10%. When the content ofvirgin materials is50%, the tensile strength of RLDPE/HDPE is23,3MPa, thetensile strength of RLDPE/LDPE is18.6MPa, the tensile strength ofRLDPE/EVA is13.8MPa. As can be seen, the tensile strength of recycledmaterials modified by EVA is similar to virgin LDPE. LLDPE, HDPE, EVA canall improve the elongation at break of recycled materials. When the content ofvirgin materials is50%, the elongation at break of RLDPE/LLDPE is391.7%,RLDPE/HDPE is321.9%, RLDPE/EVA is224.6%, RLDPE/LDPE is146.2%. Allof HDPE, LDPE, LLDPE can increase the flexural strength of recycled. Theinfluence of HDPE to the flexural strength if largest. When the content of virginmaterials is50%, the flexural strength of RLDPE/HDPE is14.1MPa,RLDPE/LLDPPE is7.9MPa, RLDPE/LDPE is7.9MPa. EVA can decrease theflexural strength of recycled materials. When the content of EVA is50%，theflexural strength of RLDPE/EVA is5.4MPa.(3) The two plasticizers can all improve the processability of recycledmaterials. Both DOP and ESO can decrease the complex viscosity, storagemodulus and loss modulus. In the frequency sweep, when the content ofplasticizers is10phr, the complex viscosity of RLDPE/DOP reduced by35.9%compared with pure recycled materials. The storage modulus reduced by37.3%.The loss modulus reduced by33.6%. In the temperature scanning, when thecontent of plasticizers is10phr, the complex viscosity of RLDPE/DOP reducedby32.7%compared with pure recycled materials. The storage modulus reducedby33.3%. The loss modulus reduced by31.1%. In the torque rheological test,Both the two plasticizers can decrease the equilibrium torque. When the content of plasticizer is10phr, the equilibrium torque of RLDPE/DOP is7.8N.m,RLDPE/ESO is8.9N.m, which indicate both the plasticizers can improve theprocessability especially DOP.(4) Lubricants have a good effect on the processability of recycled materials.When the increasing of the content of polyethylene wax, the complex viscosity,storage modulus and loss modulus of the blends decrease gradually. When thecontent of PEW is40phr, In the frequency sweep, the complex viscosity ofRLDPE/PEW blend reduced by63.7%compared with recycled materials, thestorage modulus reduced by67.6%, the loss modulus reduced by57.9%. In thetemperature scanning, the complex viscosity of RLDPE/PEW blends reduced by71.9%, the storage modulus reduced by76.4%, the loss modulus reduced by67.4%. The data of the blends is similar to virgin LDPE. In the torque rheologicaltest, whih the increasing of the content of PEW, the equilibrium torque andlargest torque decrease. When the content of PEW is30phr, the equilibriumtorque of the blend is4.9N.m, which is similar to the index of virginLDPE(4.6N.m).(5) Multi-index orthogonal experiment was used to search the optimumformula of recycled material modification. The influence of the four factors totensile strength is: DOP (B)> DCP (D)> EVA (A)> PEW (C);(b) The influenceto elongation at break is: DCP (D)> DOP (B)> PEW (C)> EVA (A);(c) Theinfluence to equilibrium torque is: PEW (C)> DCP (D)>EVA (A)> DOP (B);(c)The influence to flexural strength is: DOP (B)> EVA (A)> DCP (D)> PEW (C).The optimum formula of recycled material modification is15phr EVA,6phr DOP,30phr polyethylene wax,15phr DCP.