LDPE melt, additives

Verlaek et al. [50] have examined additives in LDPE by means of both UV and mid-IR absorption spectroscopy in film and melt samples. For the measurements a 14 mL-volume mini-extmder was used equipped with a melt-cell provided with optical channels for both UV and mid-IR measurements. UV measurements were carried out with fibre optic coupling mid-IR was performed in transmission. Single-component analysis with UV absorption on LDPE melt gave excellent results for Chi-massorb 944, Irganox 1010/1076 and Irgafos 168, all with a Standard Error of Prediction (SEP), i.e. 

Verlaek et al. [50] have used mid-IR for the determination of the non-UV absorbers Zn-stearate, Ca-stearate and oleamide (SEP values 29, 12 and 49 ppm, respectively in the melt as compared to 57, 37 and 34 ppm on film for typical nominal values of 450-1000 ppm oleamide and 1500 ppm stearates). It is again noticed that melt measurements using a 14 mL mini-extruder at 190°C often outperform polymer film measurements. SEP values for mid-IR measurements on LDPE melt containing Chimas-sorb 944, Irgafos 168, Irganox 1010/1076 were ca. 16 ppm for a complete additive package in fixed ratio concentrations (combinations of Chimassorb... 

Polyolefins are produced in a variety of forms HDPE and PP are produced as powders, while LDPE emerges from the melt preferably in the form of lenticular granules. All types, however, are supplied primarily as granules. As a rule, any thermoplastic transformation of a polymer powder to a granulate is carried out in the presence of additives. This is also partly true for pigments. 

The heat capacity is the amount of energy required to increase the temperature of a unit mass of material. It is commonly measured using a differential scanning calorimeter (DSC). The heat capacity depends on the resin type, additives such as fillers and blowing agents, degree of crystallinity, and temperature. A temperature scan for the resin will reveal the Tg for amorphous resins and the peak melting temperature and heat of fusion for semicrystalline resins. The heat capacities for LDPE and PS resins are shown in Fig. 4.15. 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Upon exiting the die, the sheet extrudate will swell to a level determined by the polymer, the melt temperature, the die length-to-opening ratio, and the shear stress at the die walls. Additionally, flow instabilities will occur at values of the corrected shear stress at the wall, of the order of, but higher than 105 N/m2, as found by Vlachopoulos and Chan (58), who also concluded that, for PS, HDPE, and LDPE, the critical Sr in slits is 1.4 times higher than in tubes of circular cross section. Aside from these differences, the information presented in Section 12.1 and 12.2 applies to slit flow. 

Tomboulian et al. (2002) has reported that butylated hydroxytoluene (BHT) can impart a "burnt plastic" odor and is an additive in HDPE pipes. Quinone may be derived from BHT due to interactions with residual chlorine in pipes (Anselme et al., 1985). Yam et al. (1996) reported that antioxidants, such as vitamin E, Irganox 1010, and BHT, contributed to off-flavors in water. Vitamin E yielded less off-flavor, possibly due to lower aldehyde and ketone concentrations. Extrusion temperatures over 280 °C and exposure time for melt contributed to more oxidation of LDPE films and higher intensities of off-flavors in water in contact with LDPE with different antioxidants (Andersson et al., 2005). 

Optionally, in the case of Fe- and Co-containing nanoparticles, the mineral oil was substituted for a mineral oil-low density polyethylene (LDPE) solution-melt. The thermal destruction was carried out at vigorous stirring at a constant temperature in the argon flow. The MCC solution was introduced into the reaction system dropwise at a constant rate. The black material produced after the addition of all the MCC solution was stirred at the synthesis temperature for 0.5 h and cooled down to room temperature. The product was extracted via rinsing the mixture with hexane. The calculated concentrations of metal-containing nanoparticles in the product resulted varied from 1 to 50 wt.%. 

As illustrated in Fig. 4, the course of changes in MWD for the additive free HDPE are very similar to those for LDPE at temperatures above its melting range. This is also the case for both the degree of LCB and the formation of insoluble material. However, compared to LDPE the formation of low MW material is more rapid for HDPE. This might be due to catalyst residues, influencing the way of decomposition of hydroperoxide groups. 

In addition to short branches from back-biting reactions, long branches are seen to be formed both in LDPE and in PVC from intmmolecular chain transfer to polymer. These are much less frequent ( 1 per 2000 repeat units) but have a great effect on the viscosity of the melt and thus the processing. This is discussed in more detail in later chapters. 

Polyethylene and polypropylene blended with iron carboxylate complexes, for example, acetylacetonate (FeAcAc) and stearates (FeSt), and irradiated by UV light under accelerated aging conditions were shown to act as effective phtoactivators giving rise to rapid photoxidation as shown from the rapid rate of carbonyl formation without any induction period (see Fig. 16.4a for FeAcAc in HDPE) and with a reduction in molar mass (see Fig. 16.2a for FeSt in LDPE). However, these complexes have been shown to cause considerable oxidation to both PE and PP during processing reflected in a sharp increase in the polymer s melt flow index (reflecting chain scission and drop in molar mass) (Fig 16.4b) and act, therefore, as thermal prooxidants and cannot be used without the use of additional antioxidants in the system [2,3,17-19,48,49]. 

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