PE blends

The interest in multicomponent materials, in the past, has led to many attempts to relate their mechanical behaviour to that of the constituent phases (Hull, 1981). Several theoretical developments have concentrated on the study of the elastic moduli of two-component systems (Arridge, 1975 Peterlin, 1973). Specifically, the application of composite theories to relationships between elastic modulus and microstructure applies for semicrystalline polymers exhibiting distinct crystalline and amorphous phases (Andrews, 1974). Furthermore, as discussed in Chapter 4, the elastic modulus has been shown to be correlated to microhardness for lamellar PE. In addition, H has been shown to be a property that describes a semicrystalline polymer as a composite material consisting of stiff (crystals) and soft, compliant elements. Application of this concept to lamellar PE involves, however, certain difficulties. This material has a microstructure that requires specific methods of analysis involving the calculation of the volume fraction of crystallized material, crystal shape and dimensions, etc. (Balta Calleja et al, 1981). 

For this reason, it is of interest to investigate the // of a model system composed of varying mixtures of two types of PE with well-differentiated microhardness values in such a way that the experimental microhardness data derived can be compared with predictions for the various component arrangements. In addition, the measurement of H of these blends at high temperature can provide direct information on the microhardness of the disordered phase. The mechanical characterization 

We can now use the new composition values and Wg to derive the microhardness H for blends of recycled PE in terms of a composite comprising two populations of crystals (the thick ones and the thinner ones). According to the additivity law 

The good agreement obtained between calculated and experimental data (Rueda et ai, 1994) confirms that the microhardness of these blends, if one uses the new 

PE/i-PP blend films were prepared by gel crystallization from semidilute decalin solution as reported by Balta Calleja et al. (1990b), using ultra-high-molecular-weight PE (M2 = 6 X 10 ) and i-PP (M , = 4.4 x 10 ). In addition to the individual PE and i-PP homopolymer dry gels, Baltd Calleja et al. investigated PE/i-PP compositions of 75/25, 50/50 and 25/75. For all compositions a concentration of about 

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Dynamic vulcanization as a method to improve the mechanical properties of NR-PE blends has been discussed in detail by Choudhary et al. [30]. The physical properties of unvulcanized and vulcanized NR-HDPE blends are given in Table 7 where notations A, B, and C indicate 70 30, 50 50, 30 70 NR-HDPE blends, respectively. The subscripts C and D denote blends containing DCP and high abrasion furnace (HAF) black (40 phr), respectively. 

In all the compositions, the DCP-cured blends showed better properties than the corresponding unvulcanized samples. Choudhary et al. [30] further demonstrated the use of EPDM, chlorinated PE, chlorosulfo-nated PE, maleic anhydride modified polyethylene, and blends of epoxidized natural rubber-sulfonated EPDM as compatibilizers in NR-LDPE (low-density PE) blends. 

The formation of the polyalloy results in improvement in the performance of the blends. This system is similar to the production of high-impact polystyrene (HIPS) where a rubber is dissolved in styrene monomer and then polymerized in the usual way. Even though the impact strength of the compatibilized PS-PE blend was higher than that of PS, it was much less than that of HIPS. In another study. Van Ballegooie and [55] have confirmed... 

For the compatible elastomer-thermoplastic blends, melting of the two polymers is the first step followed by subsequent vulcanization of the elastomeric phase. A typical mixing cycle for dynamically vulcanized NR-PE blend (DVNR) in a Brabender mixer is as follows [58] ... 

Akhtar et al. [444] have studied the effect of y-irradiation on NR-PE blend. The high-energy radiation at a high dose rate has been found to cause extensive cross-linking in the bulk. The rupmre energy values increase subsequently in the range of 15-25 Mrad and then decrease, as the absorbed dose increases further. 

The PP exhibits a sharp peak at the maximum on CL intensity whereas the HDPE curve shows a broad bimodal behavior that has been thoroughly described elsewhere [127]. In the CL curves of the blend all these features were observed, which may be a strong indication of the existence of a two-phase system in the molten state [128], although based on peroxide treatment of PP/PE blend melts. It appears that PP oxidises first and the oxidation sites created during this process accelerate, to some extent, the oxidation of the PE phase. The overlap between the PP and PE traces in the blend can be interpreted as the interface of these two phases where the PE starts oxidising. In addition, the shape of the curves confirms that the oxidation mechanisms of the resins are different and that this difference remains during the oxidation of the blend in the molten state. 

The physical interactions in TPE can be characterised by IR spectroscopy. A few examples of such studies are discussed here. Examples of PE based thermoplastic elastomers are NR/PE blends [50, 52]. TPE [49] based on 50/50 NR/LDPE, forms co-continuous morphological structure of both NR and LDPE. Thermal analysis shows that the blend is immiscible and from IR spectra of the 50/50 NR/LDPE blends [53], it is observed, the peaks of NR and PE exist almost in the same positions in the blend with a very little shift (Figure 5.12). The absorption band at 833 cm"1 for cis >C = C in NR (Figure 5.12) is shifted to 836 cm 1. Similarly the peak at 1370 cm"1 (C-H stretching of CH3 group) shifts to 1373 cm"1, while the peak for C=C double bond shifts from 1660 cm"1 to 1658 cm"1, and the band at 1467 cm"1 for -CH2 in LDPE (Figure 5.12) is shifted to 1462 cm 1. The spectra thus confirm that there exist only physical interactions in NR-PE blend. 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

Figure 17 80-K spectra of MEH-PPV/PE blend. Unoriented film. Solid line absorption. Dash-dotted line emission. (From Ref. 107.)...

The formation of keto-phosphonate structure within macromolecule leads to the removal of internal unsaturation. Triallyl cyanurate and ionizing irradiations [210] made a E-P block copolymer-PE blend thermally stable. Triallyl cyanurate increases the crosslinking density probably due to addition reactions between polymeric and allyl radicals produced by ionizing radiation. The addition of 2,2,4-trimethyl-l,2-di-hydroquinoline and bis[4(l-methyl-1-phenylethyl)pheny 1]-amine stabilized a PE-EPDM blend against heat [211]. Popov et al. [212] studied the ozone effect on PE-iPP blend. The oxidation rate was detected in relation to... 

ULDPE) enters the market as blends. One may distinguish several categories of PE-blends. 

I) PE blends with a small quantity of "external lubricant" fluoro-polymers, siloxanes, PE-waxes, etc. These blends are primarily formulated for Inqirovement of processability without affecting the PE performance (2 ). 

III) PE blends with up to 30 wt% of a rigid polymer. The additional polymer plays the filler role Increasing both the modulus and the heat deflection temperature. At low concentration, say below 5% of rigid polymer, the coiqiatlblllzatlon Is seldom necessary, but It Is a must for blends at higher loadings. 

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