Polyolefins processing

Choi, D. D. White, J, L. Polyolefins Processing, Structure, Development and Properties. (2004) Hanser Gardner Publications, Cincinnati. 

Fridman ML (1977) Crystalline polyolefins processing technology. Chimia, Moscow... 

Effect of Polyolefin Processing Temperatures on the Melt Stabilising Activity of Vitamin E... 

Spivack J D, Pastor S D, Patel A and Steihuebel L D (1985) Bis- and trisphosphites having dioxapho-sphepin and dioxaphosphocin rings as polyolefin processing stabilizers, In Polymer stabilization and degradation, Klemchuk P (Ed), ACS Symp Ser 280 247-257. 

Figure 4.1 Cracking and pyrolysis of waste polyolefin processing, main products and their application [1]. (Reproduced by permission of Hydrocarbon Processing)...

The reaction medium is initially homogeneous and the polymer forms a separate phase as the polymerization proceeds. Examples are dispersion reactions, described below, and polymerization of acrylonitrile. Various polyolefin processes discussed in Chapter 9 are other examples. 

Much of the work that has been and is being done in the field of polymer chemistry and processing is classified as confidential by many producers. In the remainder of this article, the characteristics and performance of several commercial centrifuges and their applicability to a typical, but nonspecific, multistage polyolefin process (Figure 3) are disscused. 

In the broadest sense, Ziegler Natta catalysts may be regarded as combinations of Group IV-VIII transition metal compounds with Group I-III organometallics which can effect polymerization of olefins and dienes under relatively mild conditions of temperature and pressure [82,83]. Titanium compounds and aluminum alkyls are used most frequently in commercial polyolefin processes. Both titanium and vanadium compounds are used in conjunction with aluminum alkyls in catalyst systems for synthetic rubber/elastomers. 

Bis- and Trisphosphites Having Dioxaphosphepin and Dioxaphosphocin Rings as Polyolefin-Processing Stabilizers... 

The latter is confirmed by the fact that the reaction proceeds with no loss of efficiency when performed in the presence of radical traps, or the thermal stabilizers usually used in polyolefin processing operations (38-45). The low grafting yield was obtained, both in terms of the number of bonded polar groups and of conversion levels. However, the experimental evidence reveals higher grafting yields obtained when the process occur in the melt rather than in solution (38,40,45). Scheme 13.2 once particularized for the molten state reaction media (46) drive us to the following. 

The investigation of the compatibilization and crystallization of blends of polyolefins with a semiflexible LCP leads to the following conclusions the compatibilization of polyolefin/LCP blends has been realized successfully by the addition of ad hoc synthesized polyolefin-g-LCP copolymers. The compatibilization results into materials, characterized by a stabilized morphology, improved crystallization kinetics under nonisothermal and isothermal conditions, and enhanced mechanical properties. Moreover, polyolefin processability has been enhanced by the addition of LCP, even in the presence of compatibilizers. New high quality materials with improved processability have been produced by technologies, which are economic, friendly to the environment, and socially acceptable. 

FIGURE 5.3. Gas-phase polyolefin process. From Burden, by permission of the American Chemical Society. 

Figure 2.20 Different length scales involved in a polyolefin process. Each length scale needs to be specifically integrated into a well constructed model.

Stream of oxygen, and the time is measnred between its first contact with oxygen and the onset of significant degradation as measnred by an exotherm or endotherm. This time (nsnally expressed in minutes) is the oxidation induction time of the material. The test temperature is at least 200°C (compatible with polyolefin processing temperatures) so that the specimen is molten during this test. The oxidation induction time is defined as a test method by ASTM D3895. 

In most polymers (e.g. polyolefins) process stabilisation for first use can be achieved with relatively low concentrations (0.05-0.1%) of hindered phenol or phosphite antioxidant. The stabihsation of PVC requires much higher concentrations (generally 2-4% on the PVC content) in order to combat the mechanically initiated HCl elimination referred to in Section 3. Some of them may also stabihse the polymer to the environment, but their abihty to do this depends entirely on the amormt of stabihser that remains after the reprocessing operation and how much chemical damage has been done to the pol3rmer dru ing the primary processing operation and in subsequent service. 

Next the polymer slurry is either treated in an alcohol and water wash system or fed directly to a slurry concentrating device (centrifuges) from where the wet polymer powder is fed to a dryer. After the dryer, the polymer powder is transferred to the extruder, where additives are mixed in, the powder is melted, homogenised and cut into pellets in a similar way as in other polyolefin processes. 

Polymer additives Low coefficient of friction Elame resistance Polyolefin processing to avoid surface defects Anti-dripping agents... 

Blong, T., Focquet, K. (1995) Fluoropolymer-Based Additives Improve Efficiency of Polyolefin Processing and Product Characteristics. Conference AddCon 1995, Brussels, RAPRA Technology, Shawbury, UK. 

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