New collaborative results on high performance HFFR compounds

摘要

Halogen Free Flame Retardant (HFFR) compounds have taken an increased market share over the last 40 years. The requirement of higher temperature performance of the compounds can be reached either through crosslinking or using high temperature polymers. These applications are increasingly to be found in photovoltaic, railroad (rolling stock) and automotive applications. Usually the use of a crosslinkable polymer base and ATH as a flame retardant is the cost efficient way for applications with a high volume compound demand. Nowadays, most compound manufacturers are producing crosslinkable (XL)-HFFR compounds in 2 steps: first grafting the base polymer and then filling the grafted polymer in a second step. This work reviews the use of the new 4 flight reciprocating single screw Kneader technology to produce a silane crosslinkable HFFR compound in a one-step compounding process. The one step development leads to a big improvement in energy efficiency, lower heat history and much easier material handling and production logistics for the compounder. The ability to achieve this complicated reaction in a single compounding step is possible due to an extended process length of 22L/D which is 7L/D longer than the "standard" 15L/D process length. The split barrel construction of the reciprocating single screw Kneader is a very practical feature that allows the machine to be stopped and opened. It also allows for directly observing the correlation between temperature profile as measured in the thermocouples and that as seen in the actual process according to the various stages of mixing along the length of the barrel. This paper describes the results obtained with a HFFR formulation based on a polar and a non-polar polymer mixture. Also the influence of ATH loading in the non-polar PE base formulation was evaluated. The following properties were tested in the laboratory: degree of crosslinking, tensile strength, elongation, aging, water take up and flame retardant performance (Cone Calorimeter). The measured properties are shown and are extremely promising for further development into the formulation of the final application. The lower energy consumption of the 1-step compounding process leads to remarkably lower energy costs and clearly allows a much improved ecological footprint. The energy savings are some 60kWh/t on the kneading step corresponding to a reduction of around 29%. This translates during one year to a cost saving on electrical energy of 70'000USD (Energy price: 10Cents/kWh; output of compounder: 2000kg/h). The shelf live of a crosslinkable compound is often limited to 6 month when packed in hermetic sacks. The polar and non polar formulations were both stocked in the warehouse at ambient conditions in regular PE bags to test for any premature crosslinking during storage. The samples were extruded every 3 months. After 6 months no significant change in the MFI, tape quality or mechanical properties was observed nor any precrosslinking. The cross-linkable HFFR compound can also be used as a thermoplastic HFFR compound when extruded without the catalyst masterbatch.