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VISCOSPEED in HFFR compounds: Big impact with minimal dosage
INTRODUCTION Demand for halogen free flame retardant cable materials (HFFR) has grown consistently over the past few decades, due largely to the reduction in smoke and the absence of toxic and corrosive fumes in the event of fire when compared to traditional halogenated flame retardant materials. These HFFR materials are typically polyolefin compounds with a high loading of inorganic flame-retardants such as aluminium hydroxide (ATH) and magnesium hydroxide (MDH). A new harmonised European
Construction Products Regulation (CPR) came into effect in July 2017 with the aim of further reducing fire risk. It requires that cables should delay the outbreak of fire and cause minimal smoke emissions. This goal is generally achieved by increasing the inorganic flame retardant filler content. For the most demanding applications it may be necessary to add as much as 65-80% of appropriate filler. This, of course, has challenging consequences with regard to processability and mechanical properties for both producers of cable compounds and for cable manufacturers. In VISCOSPEED, Innospec Leuna GmbH
has developed a halogen-free, low-dosage, organic processing aid that minimises the
Table 1. EVA-based sheathing compound Ingredient
EVA VAc=28% MFI=3 C8
-POE d=0.868 MFI=0.5 mLLDPE MFI=3-5 LLDPE-g-MAH VISCOSPEED
Fine pp ATH BET=4 m2 /g
Coated milled MDH 3.5µm Silicone Masterbatch Stabiliser TOTAL
PROPERTIES
MFI – 21,6kg@190°C Tensile strength [N/mm2 Elongation at break [%]
4 ]
14,5 190
7 13 190
12 11
190 (1A)
Standard 19,5 5 5 5 -
52 12 1
0,5 100
negative impact of increased filler loading on processing without negatively affecting flame retardant properties. VISCOSPEED has been shown to improve the dispersion of ATH and MDH, as well as carbonates and silica-based nano-materials, across many different cable compounds, demonstrating improved flow during processing and manufacturing. VISCOSPEED, which is polar by nature,
enables fast wetting and dispersion of inorganic filler particles in the polymeric matrix. Moreover, it prevents fine filler particles re-agglomerating during processing, which ensures the filler makes the maximum contribution to flame retardancy. This is especially useful where milled natural fillers are deployed, such as milled MDH, and where inorganic synergistic additives such as nano- silica, sepiolite and nanoclays are used. Ultimately, the interaction between the polar filler and the VISCOSPEED additive results in optimised dispersion and char formation and reduces dripping tendency.
VISCOSPEED IN SHEATHING COMPOUNDS The sheathing of the cable is a critical component in terms of protection from mechanical shocks and flame retardancy.
(1B) 1%
VISCOSPEED 19,5 5 5 4 1
52 12 1
0,5 100 (1C) 2%
VISCOSPEED 19,5 5 5 3 2
52 12 1
0,5 100
Addition of VISCOSPEED to highly flame retardant sheathing compounds has been shown to significantly improve processability without negative effect on elongation at break, aging behaviour or flame retardancy. Data for an EVA-based cable sheathing compound (Table 1) shows that, despite a reduction in the level of maleated coupling agent in the formulations using VISCOSPEED (compounds 1B and 1C) the tensile strength is maintained above the critical value of 10 N/mm2
. Due to its polarity, VISCOSPEED acts as a
co-compatibiliser and can partially replace the maleated coupling agent. As the data in Tables 1 and 3 show, replacing 2% LLDPE- g-MAH with the same level of VISCOSPEED allowed a substantial increase in flowability (MFI) to be achieved without affecting elongation at break. The improvement in processability means that costly synthetic fillers can be replaced by much less expensive natural milled materials (Table 2). VISCOSPEED can also be used to
advantage in sheathing compounds based on POE (polyolefin elastomer) resins. POE is of interest to cable producers for its excellent combination of mechanical properties, flexibility, and very wide application temperature range (extending from -60°C to 125°C). However, standard POE cable sheathing formulations tend to drip when burning (see results for compound 3A in Table 3). A number of studies have been carried
out by Innospec Leuna to explore the effect of the addition of VISCOSPEED to POE-based formulations containing both coated and uncoated natural MDH. All have shown similar results in that processing was improved without deterioration of the most important performance parameters. Data in Table 3, for example, shows that the introduction of VISCOSPEED both eliminates burning drops during vertical fire tests and improves elongation. These effects are attributed to the ability of VISCOSPEED to allow a finer dispersion of the natural filler in the compound.
VISCOSPEED IN BEDDING COMPOUNDS Finally, the use of VISCOSPEED has also been investigated in several different bedding compounds. Similar to the earlier examples, VISCOSPEED has been demonstrated to maintain easy processing
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