HDPE, additives Carbon-blacks

For the experiments a multimode frequency microwave system was applied. The effectiveness differs between carbon based and the reference susceptors. Suitable heating conditions to melt HDPE by carbon black heating promoters were 400 W at a time of only 20 s. With those parameters the remaining noncarbon based additives did not show any heating. It was necessary to fix the power up to 1000 W and 120 s to ensme a suitable and comparable heating process for all tested material combinations (Table 2.3). 

Elongation was better retained also by the addition of 5% soot to LDPE. The material underwent a rapid erosslinking at 50-60 kGy whieh improved its elongation by a faetor of 4. At the same time, its tensile strength was decreased by 30%." Polyethylene eontaining earbon blaek was found to be resistant to ionizing radiation. The impact strength of carbon black filled HDPE and HDPE/EPDM was improved after exposure to Y-radiation. ... 

The results presented here illustrate the general feasibility of this technique. They relate primarily to the behavior of thermal and current noise in the glass transition (Tg) or melting (Tm) region of an amorphous (polystyrene) and a crystalline (HD-polyethylene (HDPE)) polymer rendered conductive by the addition of minor amounts of carbon black, and further they relate to the noise of aqueous solutions of certain polymers during Couette flow. Because of experimental diflBculties, noise measurements on solid polymers during deformation and flow have not yet produced useful results. 

The HDPE, LDPE, and LLDPE can be stabilized by UV absorbers of type benzophenone or benzotriazole and also combination of HALS and UV-absorbers. Usually pipes used in irrigation are pigmented with white titanium dioxide or carbon black. Titanium dioxide may be used up to an additional level of 0.5 wt%. Each of the HALS and UV absorber may be added up to 0.05 wt% [50-53]. 

Fig. 18.21 (a) Effects of addition of Irganox B225 (1 1 blend of Irganox 101 and Irgafos 168) on repetitively extruded (up to five times) HDPE. The stabilizer was added in the amount of 0, 0.05, and 0.20 wt% (After Herbst et al. 1997). (b) Stabilization effects of HALS on a virgin and recycled LLDPE/LDPE blends with and without carbon black (CB) (After Herbst et al. 1997)... 

Oxidative degradation and the importance of antioxidant additives have already been discussed in detail in Sect. 5.2.2. T q)ically, phosphite and a hindered phenol are used as the main components of the antioxidant package for most of the HDPE geomembranes available on the market. Normally, carbon black is added as UV stabiliser. The concentration of the antioxidant components is t3 ically in the range of a few thousand ppm (mg/kg). Depletion of these antioxidants was identified as the relevant... 

Most of the resins used for HDPE geomembranes are ethylene-a-olelhi-co-polymers and should therefore rather be classified as hnear low density or linear medium density HDPE. Although only the carbon black additive places them formally into the high-density range, the geosynthetic cormnunity customarily refers to them as HDPE geomembranes. 

It is well known from pipe pressure tests that immersion in water enhances antioxidant migration in comparison to air, as was observed in our experiments. Smith et al. attributed this to the influence of carbon black (Smith et al. 1992). Antioxidants are adsorbed at the earbon black surface, whereby the migration process is retarded considerably. During immersion in water some moisture is also present in the HDPE bulk material and this is preferentially adsorbed by the carbon black aggregates. The adsorption of water thereby supersedes that of the antioxidants and decreases the retardation coefficient and increases the apparent diffusion coefficient of the latter. In addition, it was suggested that the antioxidant forms loosely bonded clusters within the dry PE bulk material which may disperse slowly in contact with diffusing water thus enhancing the antioxidant diffusion coefficient (Le Poidevin 1977). 

As mentioned previously, the most important pigment additive employed for light stability purposes is carbon black. The addition of 2% by weight of a well-dispersed carbon black of fine particle size should extend the outdoor life of most low- and HDPE to as much as 20 years in temperate climates, while even the addition of 0.2% should give 10 years ... 

Fig. 82 Stabilization effects of the addition of carbon black into HDPE. Temperature 180°C.Environment air. The data were taken from [03J2]. (a) CL curves CB concentration (1) free, (2) 0.075 %, (3) 0.15 %, (4) 0.25 %. (b) dependence of the induction time of oxidation on carbon black concentration.

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