LDPE, additives Accelerators

The plastic bottle and dispensing tip is made of low-density polyethylene (LDPE) resin, which provides the necessary flexibility and inertness. Because these components are in contact with the product during its shelf life, they must be carefully chosen and tested for their suitability for ophthalmic use. In addition to stability studies on the product in the container over a range of normal and accelerated temperatures, the plastic resins must pass the USP biological and chemical tests for... 

A high extrusion temperature, followed by corona treatment which causes oxidation, was used for the PE layer of the cartons, whereas the PE liner for the "bag in the box" is a LDPE extruded at a lower temperature and without corona treatment. This study, therefore, indicates that an oxidized polymer surface may accelerate reactions resulting in a reduced shelf-life. These results were confirmed by Durr (10) who presented the effect of high temperature extrusion lamination of an Ionomer on development of off-flavors. In recent years carton packs are coated with an additional layer of low temperature extruded PE in order to reduce the above effects. 

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]. 

For example, Tai et al. [54] investigated the reaction kinetics of foaming. The crosslinking reaction of an LDPE/DCP system is controlled by a first-order decomposition of DCP. The addition of ZnO into AZD not only lowers the decomposition temperature, but also accelerates its decomposition. The reaction kinetics of the LDPE/AZD/ZnO system was found to be similar to those of the AZD/ZnO system. The numerical results of this paper could be used as a framework for future prediction and simulation of these processes. 

Based on the findings of accelerated weathering by xenon tests and natural (outdoor) weathering for films of LLDPE and LDPE resins, it was concluded that PE films containing additives, particularly hindered amine stabilisers (HAS), have a UV stability four times higher than the corresponding pure films [43]. 

In a few cases, the addition of minor amounts of immiscible or miscible polymers results in the nucleation of a crystalline polymer. The nucleation of PP by PE and polyamides (e.g., PAl 1) (immiscible) as well as the addition of PP to poly(butene-l) (miscible) has been noted in the literature [138-141 ]. The addition of LDPE to PP showed a reduction in the spherulite size of PP, attributed to an increase in nucleation density of the a-crystalline form along with an increase in the rate of growth of the -crystalline form [141]. The nucleation of polycarbonate by the zinc salt of sulfonated polystyrene ionomers was noted to occur with both miscible and phase separated blends [142]. Nanometer sized ionic aggregates appeared to contribute to the polycarbonate nucleation. A liquid crystalline copolyesteramide (Vectra-B950 ) was shown to accelerate the crystallization of poly(phenylene sulfide) [143]. This effect was not concentration dependent and did not change the level of crystallinity. 

TPEs of SBS (and SEBS)-type are versatile. Compared to PVC compounds, ester plasticizers cannot be used in TPE compounds. Vulcanizing agents such as accelerators, sulfur, or peroxides are not required in SBS-type TPE block copolymers. EPDM is blended with SBS to increase ozone resistance. PS, polyethylene (LDPE, LLDPE, HDPE), and polypropylene (PP) are used as additive polymers with SBS and SEBS. Polystyrene (PS) is compatible with B-S block copolymers. Polystyrene is useful to adjust properties and cost of SBS compounds. The addition of polystyrene into SBS increases hardness, modulus, tensile strength, tear strength, and abrasion resistance. Styrenic resin (a-methyl styrene) can be used as a blend with PS or as an alternative for SBS compound. This resin can be used as a blend with polystyrene as an alternative. Styrenic resin enhances flow properties and physical properties. It is more compatible compared to polystyrene and assists in adhesion and coherent processing. 

Two PEs (HDPE and LDPE) were used with the addition of small amount of a nucleating agent masterbatch. The basic properties are listed in Table 1. The nucleating agent masterbatch is the exothermic particles in a PE base resin, and accelerates the small and uniform cell formation with the injected gas. 

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