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Processing aid for production of HFFR composites
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Novel high-speed silane-based XL-HFFR formulations
In 2023, the fastest growing energy generation technology was photovoltaic (PV), with a total addition of 447 GW capacity. Typically, 5% of the total investment for PV is allocated to cables, especially crosslinked halogen free flame retardant (XL-HFFR) cables play a crucial role. The cables need to have high heat resistance level, good mechanical properties and long durability. These properties are achieved during a cross-
linking process, as polymer chains are linked to each other, forming covalent bonds. In this case, a thermoplastic polymer such as polyethylene is transformed into a thermoset polymer. Performing crosslinking using silanes, brings
many benefits, as it is e.g. initiated by moisture from air after the processing step. Therefore, it does not require an additional plant investment. Thus far, many companies fail to produce XL-HFFR compounds using a twin-screw extruder. The high friction during processing initiates the degradation of the inorganic flame retardant (ATH or MDH) yielding an undesired premature crosslinking. This filler degradation at increased
temperatures is the reason why presently only cost-intensive synthetic MDH is used in Si-based cross-linkable HFFR compounds produced using a twin screw extruder. VISCOSPEED, as powerful dispersing aid and effective internal lubricant, is able to prevent this issue. The quick wetting and therefore smooth processing reduces local hot spot formation which permits the use of more thermally labile FR filler, such as ATH. In our recent study we show that synthetic
ATH or even natural MDH can be applied to achieve easily processable and cost-beneficial XL- HFFR formulations produced applying one-step compounding. Initially the replacement of high temperature stable synthetic MDH by less stable synthetic ATH was not successful as the temperature went too high. Once we introduced VISCOSPEED, all process parameters and especially the flowability was improved massively (Formulation 1 in the table). The next and ultimate step is the use of
natural, commercially abundant and cost- beneficial MDH. To achieve this, we introduced it in the form of a concentrate (MB MDH 80%) to solve all issues related to the high surface area of
Table 1. XL-HFFR Formulation
VISCOSPEED HP POE 0.87 MFI 6
mLLDPE 0.918 MFI 3 Additives
Grafting mixture MB MDH 80% Synthetic ATH
Process parameter Pressure [bar] Torque [%] T max [°C]
Properties MFI 160°C@21,6 kg Surface
Tensile [N/mm2 E@B [%]
] HST@200°C [N/mm] Graph 1: Cable extrusion
Formulation 1 3
18 18 2 1
58 44
70-80 201
16
smooth 12
292 250 - 15
Formulation 2 3
16 16 2 1
20 42
47
70-80 203
11
smooth 10
320 50 - 5
the natural form. VISCOSPEED is also a key ingredient to achieve a homogeneous and well flowing compound. Such a concentrate of 80 % natural MDH was
used in Formulation 2. Yielding almost the same processability compared to the synthetic filler. The mechanical properties of both formulations are in a similar and good range. Our formulations were even tested during
cable extrusion, and the addition of VISCOSPEED yielded an increased processing speed at our customer (Graph 1).
To learn more about VISCOSPEED and the beneficial pre-dispersion of natural fillers and how your formulation can benefit please check
www.VISCOSPEED.com and get in touch with us.
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