New developments in solid-state modification of polypropylene
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - Poster (CPD&E - P)
Keywords: polypropylene, long chain branches, solid-sate modification, rheology, strain-hardening
Introduction
The modification of isotactic polypropylene (iPP) in the solid state has been widely investigated in the past 10 years in order to modify the chemical structure of the PP backbone, while at the same time the degradation reaction via beta-elimination should be avoided [1-3]. In particular an industrial process (Hivalloy), in which iPP is grafted with several vinyl monomers by means of a radical mechanism, has been developed by Basell. The final product is characterized by a very fine morphology in which the in-situ polymerized component is dispersed in the form of small droplets (inclusions of the order of 100 nm) in a PP matrix. On the other hand, long-chain branched iPP (LCB-iPP) constitutes a very important basic material for many applications and processes (among others blow molding and extrusion coating). Current technologies for production of LCB-iPP include the use of irradiation and melt modification techniques. Aim of this work is to investigate the possibility to combine the advantages of solid-state modification with the production of LCB-iPP.
Results and Discussion
In this work we present first the scientific basics of solid state modification of polypropylene via radical mechanism. In particular attention is paid to the use of radical reactions in the solid state and to the grafting reactions onto iPP. We then discuss the latest developments of iPP modification in the solid phase. In particular focus will be directed to the formation of long chain branches (LCB) via solid-state modification. From a product technology point of view, the presence of LCB is an essential prerequisite for applications of iPP in the production of foams or films. Indeed LCB-iPP, contrary to normal iPP, shows pronounced strain-hardening behavior in extension, i.e. a significant increase of viscosity with the strain. A radical initiator (peroxide) and several (multifunctional) co-agents have been used in this work to obtain the desired macromolecular structure. The rheological behavior together with the determination of the molecular weight by gel permeation chromatography (GPC) clearly indicate the formation of LCB-iPP. To the best of our knowledge this constitutes the first example of a solid-state process (not including the use of irradiation techniques) to obtain a LCB-iPP. This new process will be briefly compared to the established ones in order to underline its advantages and disadvantages as compared to the current technology. Due to the very large choice of possible co-agents, very simple criteria for the choice of the co-agent will be further discussed.
References
1. R.Rengarajan, M.Vicic, S.Lee, J.Appl.Pol.Sci., 39, 1783 (1990)
2. E.Borsig, L.Hrckova, J.Macromol.Sci-Pure Appl.Chem., A31(10), 1447 (1994)
3. M.Ratzsch, H.Bucka, C.Wohlfahrt, Angew.Makromol.Chem., 229, 145 (1995)
Presented Wednesday 19, 13:30 to 15:00, in session Chemical Product Design & Engineering - Poster (CPD&E - P).
