HDPE/LDPE melt

Nova Chemicals HDPE, LDPE, LLDPE, MDPE, Melt Compounded Black Polystyrene HIPS, GPPS, Reprocessed, Specialty Polystyrene... 

Figure 3.13 shows the shift factors aT determined from time-temperature superposition as a function of temperature for melts of two semi-crystalline thermoplastics as well as the Arrhenius plot. For the two polyethylenes (HDPE, LDPE), the progression of log ax can be described with the Arrhenius equation. The activation energies can be determined from the slope as Ea(LDPE) 60 kj/mol and Ea(HDPE) 28 kj/mol. Along with polyethylenes (HDPE, LDPE, LLDPE), other significant semi-crystalline polymers are polypropylene (PP), polytetrafluoroethylene (PTFE) and polyamide (PA). 

In 1978 Union Carbide reported a special manufacturing process called Unipol that gave linear low-density polyethylene (LLDPE). Linear low-density polyethylene may contain small amounts of butene or octene as co-monomers. The structural differences between HDPE, LDPE, and LLDPE are shown schematically in Fig. 6.1. These structural features determine physical properties such as elasticity, crystallinity, melt-flow index, etc. of the resultant polymers. 

An illustrative example of the previous considerations may be given for polyethylene melts. It is admitted that low density polyethylene (LDPE) melts develop rapid vortex growth in an abrupt contraction, and that high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) melts do not. However, in exit flows, all these polyethylene melts can swell notably, and, for many years, there has been no clear understanding about differences in entry and exit flows of these polymer melts. 

Santamaria and White (24) studied melt flow behavior and splnnablllty of several polyolefin systems including HDPE/LDPE blends. Defining the steady state compliance as ... 

The most Important commercial blends of PE are those of LLDPE with LDPE (25, 26). The capillary flow data n (012) and B 8(012), Indicated (similar to HDPE/LDPE) PDB-type behavior (27-29). The latter authors also reported a PDB relation between melt strength and composition. Kecently (14, 15) these blende were studied under the steady state and dynamic shear flow as well as in uniaxial extension. A more detailed review of these results will be given in part 3 of this chapter. Like HDPE/LDPE blends, those of LLDPE/LDPE type are also consistently reported as immiscible. 

U.S. Pat. No. 7,022,751 [111] describes a fiber-reinforced composite plastic material comprising thermoplastic polymers such as HDPE, LDPE, polypropylene, PVC, and polystyrene a high melting point waste polymer fiber material such as polyethylene terephthalate and nylon, an inorganic filler, such as glass and other material, and an organic filler such as wood or particles of a thermoset plastic, such as rubber and polyurethane foam. 

HDPE LDPE Toughened HDPE with improved processing, especially melt strength HDPE and LDPE are immiscible... 

Figure 3.5 DSC melting curves for HDPE, LDPE, and their 1 1 blend.

These PE polymers offer a broad spectrum of structures, properties, and applications. However, the blending of different types of PEs (HDPE, LDPE, LLDPE, and UHMWPE) has attracted growing interest because of the potential for obtaining low cost materials with improved mechanical properties and better processabilities, as compared to those of the pure constituents (1-34). Nowadays, 70% of PEs in the market are blends (24). The processability and properties of PE blends are dependent on the melt miscibility. Moreover, the properties are also dependent on the morphological structure of the blend, which is basically a combination of the crystallization behavior and melt miscibility. Therefore, the miscibility and crystallization behavior of PE blends have been prevalent research topics over the last two decades. 

Uses Antioxidant, metal deactivator for polymers, PP, HDPE, LDPE, some thermoplastic elastomers used as primary insulation in wire/cable applies., EPDM, peroxide- and radiation-crosslinked PE, nylon, polyacetal, polybutene, PU, styrenic copolymers, unsat. rubber, PVC, PVB, hot-melt and sol n. adhesives, powd. coatings, metal coatings, rubber/plas-tic gaskets, plastic fabricated parts in contact with catalytic metals, oils/ lubricants in contact with metals, food pkg. 

SANS experiments have indicated that blends of high density (linear) and long-chain branched low density polyethylenes (HDPE/LDPE) are homogeneous in the melt, though the components may separate on slow cooling due to the difference in crystallization mechanisms [43]. The semicrystalline blends form effectively two-phase systems in the solid state, and it was shown [43,44] that the Debye-Bueche (DB) [45,46] model was appropriate to describe the morphology, with a SANS cross section of the form... 

Figure 11. DSC melting curves of HDPE/LDPE blends, = 2.5 K/min.

The different types of polyethylene derive from differences in the polymer chains, which in turn result in variations in melting points, densities, properties and therefore applications (see Table 2.4). It may be necessary to specify the type of polyethylene being referred to, e.g., HDPE, LDPE or LLDPE. 

Most of the thermoplastics used for extrusion and injection molding are used in the IBM process. Some of the resins are especially formulated for use on IBM machines. Easy flow, metal release, heat stability, and melt strength are some of the properties, which are specihcally designed into materials for IBM processing. Resins currently processed on IBM equipment include HDPE, LDPE, PS, ABS, PP, PVC, Barex, PET, TPR, polysulfones, polycarbonate, Amidel, acetal, and polyarylate. 

Monofilament is usually extruded using a conventional screw extruder of rather small size, through a die consisting of a series of holes. The monofilaments are extruded downward into a tank of water (quench tank) from which they go to pull-rolls to he drawn and oriented. The physical properties of the strands depend on the conditions of extrusion, on the degree of stretching, and on the temperature at which they are stretched. For HDPE, a melt temperature of between 260 and 290 °C is usually best. For LDPE, about 30 °C lower is better. Strength increases with draw ratio and generally levels out at ratios between 9 1 and 12 1. 

The properties of LDPE are those expected of a lower-crystallinity variant of HDPE the melting point is lower, approximately 115°C, varying with density, (Figure 6.5), with a more gradual melting process. It is almost a factor... 

As noted at the beginning of this chapter, the structure and properties of LLDPE are comparable with those of LDPE, with the notable difference that LLDPE does not have long-chain branching. The practical consequence is that LLDPE has much superior strain accommodation, which allows far greater draw-down, both in the melt and in the solid state. It is interesting to compare the tensile stress vs. strain curves for HDPE, LDPE and LLDPE (see Figure 6.8). 

The amounts of HDPE in a blend and the shear rate were chosen as independent variables in this study. Experiments were carried out in the melt state at 190°C. A Goodrich method was used for determination of effective instrument dimensions, which allows one to employ the Daane et al procedure in order to relate torque-rheometer data to more fundamental rheological values. The same HDPE/LDPE ratios were used in the study of mechanical behavior of HDPE/LDPE system of injected specimens. As said previously, DSC thermograms were used to determine weight concentration of two crystalline components both in HDPE/LDPE blends and wastes. 

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