Twin-screw extruder, blending performances

The aliphatic-aromatic poly(ester)s discussed above are prepared from butanediol and a mixture of adipic acid and terephthalic acid. Blending can be performed on twin-screw extruder equipped with a medium shear mixing screw. 

Several studies have been performed to evaluate the mixing capabilities of twin screw extruders. Noteworthy are two studies performed by Lim and White [12,13] that evaluated the morphology development in a 30.7 mm diameter screw co-rotating [28] and a 34 mm diameter screw counter-rotating [3] intermeshing twin screw extruder. In both studies they dry-mixed 75/25 blend of polyethylene and polyamide 6 pellets that were fed into the hopper at 15 kg/h. Small samples were taken along the axis of the extruder and evaluated using optical and electron microscopy. 

To toughen PA, 2-5 wt% of either PO, elastomer, ionomer, acidified or epoxidized copolymer may be added. PA/PO blends of type (2) were developed to improve dimensional stability and to reduce water absorbency of PA. Alloying PA with PO reduces the rate of water migration to and from the blend, but not the inherent water absorption of PA [Utracki and Sammut, 1991, 1992]. The alloying is either a two- or three-step reactive process (1°) acidification of PO, (2°) preparation of a compatibilizer, and (3°) compounding PP, PA, and the compatibilizer. Usually, the reactive blending is carried out in a twin screw extruder [Nishio et al., 1990 Hu and Cartier, 1998], Since it may cause reduction of the blend crystallinity (thus performance), the extend must be optimized. The rigid PA/PP blends usually comprise PA PP =... 

PP/EPDM Blends To improve impact properties of PP, the resin is usually modified by incorporation of an elastomer. Since the performance depends on morphology, radiation crosslinking was used in its stabilization [van Gisbergen et al., 1989a] (Table 11.9). The blends were made either in a two-roll miU, at 185°C, then compression molded into 1-mm-thick sheets, or in a co-rotating twin-screw extruder, then pelletized. The irradiations (100 kGy) were done using a 3-MeV electron accelerator. Irradiated and non-irradiated pellets were injection-molded. Eor the DSC measurements, the samples were melted at 200°C, quenched to 110°C, and then heated at a rate of 10°C/min. 

For example, twin-screw extruders with 80 tons/hr throughput and injection (100,000 kN) molding presses with shot size of 100 liters of polymer are available. Composites where the matrix is a polymer blend that comprises six different polymers have been introduced. Gas and multiple injection processes, melt-core technology, solid-state forming, microcellular foams all lead to new products with advanced performance. The polymer industry is becoming increasingly sophisticated. 

A peroxide-induced reactive compounding of PP/GRT blends in a corotating twin-screw extruder was carried out to prepare thermoplastic elastomer alloys (Wiessner et al., 2012). The extrusion experiments showed that the width of the residence time distribution was the key parameter determining the mechanical properties of elastomer alloys, whereas the mean residence time had little effect. This was confirmed by performing both quasi-static and cyclic tensile tests. 

In 1987 Utracki and Schlund characterized a series of ten Z-N-LLDPEs, LDPE, and their LLDPE/LDPE blends (Utracki and Schlund 1987 Schlund and Utracki 1987a, b). Properties of the ten experimental resins are listed in Table 18.8. Since for full evaluation of performance a large quantity of material was needed, the blends were compounded in a corotating twin-screw extruder (TSE), using commercial LPX-30, LLDPE-10 (both Z-N-LLDPE), and LDPE-102. Two series of blends were prepared Series 1 of LPX-30 with LLDPE-10 and Series 11 of LPX-30 with LDPE-102. The miscibility was judged from the location of the Gross relaxation spectra maximum (Eqs. 18.12, 18.13, and 18.14). Two dependencies for the... 

Materials used, kindly obtained from DSM (the Netherlands), were PP 13E 10 (polypropylene) and two types of EPDM, Keltan 514 and Keltan 578. Before exposure to irradiation PP was first compression moulded into sheets with a thickness of 1 mm. Blends were made on a two roll mill (Schwabentahn, T = 185°C) and the blends were also compression moulded into 1 mm thick sheets. Some of the blends were made on a corotating twin-screw extruder (Berstorff ZE25) and were pelletized. Both sheets and pellets were exposed to electron beam irradiation which was performed... 

Melt blending is also carried out using a twin-screw extruder. The serew speed is determined by the ease of processing and mechanical properties of the blends. The extrudate is quenched in a water bath at room temperature and pelletized. The blends are dried in a vacuum oven and re-extruded using the previous extrusion conditions. The blends are again dried in an oven and kept in a desiccator at room temperature. Tanrattanakul et performed melt... 

Performance of EFM attached to a singe-screw extruder, SSE, was evaluated examining its suitability for 1. Dispersion of viscous polymer in low viscosity matrix (where X > 4) 2. Impact-modification of engineering resins 3. Elimination of gel particles from either R-TPO or EVAc reactor powders 4. Dissolution of UHMWPE in HDPE, etc. For comparison, the blends were also pr ared using a co-rotating, intermeshing twin-screw extruder, TSE, equipped with high dispersion screws [42, 43 ]. 

In the blending process, whiskers may become damaged or even broken because of the impact and collision between whiskers and resin particles and the shear caused by the rotation of the screw. The constant length-to-diameter (Z/D) ratio of whiskers is the key for filling modification, so the speed of extrusion, the temperatures of different sections, and the position of the feed inlet of whiskers greatly influence the performance of the composite materials. Ge adds whiskers from the feed inlet of the twin-screw extruder and the first outlet respectively, and the performances of the composite material are shown in Table 4.2. 

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