Aramid fibrils
Aramid fibrils having in the wet phase a Canadian Standard Freeness (CSF) value less than 100 ml, after drying a specific surface area (SSA) less than 7 m 2 /g, and a weight weighted length for particles having a length >250 μm (WL 0.25) less than 1.2 mm, are described. A method of preparing the fibrils includes the steps (a) polymerizing an aromatic diamine and an aromatic dicarboxylic acid halide to an aramid polymer, in a mixture of N-methylpyrrolidone or dimethylacetamide and calcium chloride or lithium chloride to obtain a dope wherein the polymer is dissolved in the mixture and the polymer concentration is 2 to 6 wt. %, (b) converting the dope to fibrils by using a jet spin nozzle under a gas stream, and (c) coagulating the fibrils using a coagulation jet.
1. Aramid fibrils having in the wet phase a Canadian Standard Freeness (CSF) value less than 300 ml and after drying a specific surface area (SSA) less than 7 m 2 /g and a weight weighted length for particles having a length >250 μm (WL 0.25 ) less than 1.2 mm, wherein the fibrils are substantially free of fiber stems.
2. The fibrils of claim 1 wherein the aramid is poly(para-phenylene terephthalamide).
3. A paper made of constituents comprising at least 2 wt. % of the aramid fibrils of claim 1 .
4. A paper made of constituents comprising at least 5 wt. % of the aramid fibrils of claim 1 .
5. A paper made of constituents comprising at least 10 wt. % of the aramid fibrils of claim 1 .
6. The fibrils of claim 1 wherein in the wet phase the CSF value is less than 150 ml and after drying the SSA is less than 1.5 m 2 /g.
7. A paper made of constituents comprising at least 2 wt. % of the aramid fibrils of claim 6 .
8. A paper made of constituents comprising at least 5 wt. % of the aramid fibrils of claim 6 .
9. A paper made of constituents comprising at least 10 wt. % of the aramid fibrils of claim 6 .
10. The fibrils of claim 1 wherein the aramid is para-aramid.
11. A paper made of constituents comprising at least 2 wt. % of the aramid fibrils of claim 10 .
12. A paper made of constituents comprising at least 5 wt. % of the aramid fibrils of claim 10 .
13. A paper made of constituents comprising at least 10 wt. % of the aramid fibrils of claim 10 .
14. A method of preparing the fibrils of claim 1 comprising
a. polymerizing an aromatic diamine and an aromatic dicarboxylic acid halide to an aramid polymer, in a mixture of N-methylpyrrolidone or dimethylacetamide and calcium chloride or lithium chloride, to obtain a dope wherein the polymer is dissolved in the mixture and the polymer concentration is 2 to 6 wt. %,
b. converting the dope to fibrils by using a jet spin nozzle under a gas stream, wherein the fibrils are derived directly from the dope and are not derived from a pulp, and
c. coagulating the fibrils using a coagulation jet.
15. The method according to claim 14 wherein at least part of the hydrochloric acid formed is neutralized to obtain a neutralized dope.
16. The method according to claim 15 wherein the ηrel (relative viscosity) of the aramid polymer is between 2.0 and 5.0.