Method for manufacturing low-molecular-weight polytetrafluoroethylene
The invention relates to a method for manufacturing low-molecular-weight polytetrafluoroethylene, comprising: a) a first step of mixing high-molecular-weight polytetrafluoroethylene with at least one additive selected from the group consisting of ethers having formula R 1 —O—R 2 , wherein R 1 and R 2 are independently selected among C 1 -C 10 straight or branched aliphatic group, C 4 -C 10 alicyclic or heterocyclic groups, C 5 -C 10 aromatic or heteroaromatic groups; (per)fluorinated vinyl ethers; (per)fluorinated olefins; and optionally substituted aromatic hydrocarbons, and b) a second step of irradiating the so obtained mixture with ionizing radiation, said second step b) being carried out substantially in the absence of oxygen.
1 . A method for manufacturing low-molecular-weight polytetrafluoroethylene (PTFE), comprising:
a) a first step of mixing high-molecular-weight polytetrafluoroethylene (PTFE) with at least one additive selected from the group consisting of:
ethers having formula R 1 —O—R 2 , wherein R 1 and R 2 are independently selected among C 1 -C 10 straight or branched aliphatic group, C 4 -C 10 alicyclic or heterocyclic groups, C 5 -C 10 aromatic or heteroaromatic groups and wherein R 1 and R 2 may form a C 4 -C 10 aliphatic cyclic structure, optionally comprising heteroatoms; (per)fluorinated vinyl ethers; (per)fluorinated olefins; and aromatic hydrocarbons substituted with one or more straight or branched alkyl or alkoxy group and/or halogen atom, and
b) a second step of irradiating the so obtained mixture with ionizing radiation,
said second step b) being carried out substantially in the absence of oxygen.
2 . The method according to claim 1 wherein the low-molecular-weight PTFE has a melt flow index of at least 0.1 g/10 min, determined according to ASTM D 1238 by applying a weight of 10 Kg at 372° C.
3 . The method according to claim 1 wherein the high-molecular-weight polytetrafluoroethylene (PTFE) has a standard specific gravity, determined according to ASTM D4895, of at least 2.130.
4 . The method according to claim 1 , wherein said at least one additive is an ether of formula R 1 —O—R 2 , wherein R 1 and R 2 are independently selected from the group consisting of C 3 -C 6 straight or branched aliphatic groups.
5 . The method according to claim 4 , wherein R 1 and R 2 are butyl groups or isopropyl groups.
6 . The method according to claim 1 , wherein said at least one additive is a (per)fluoroalkyl vinylether (MVE) having formula:
CF 2 ═CFOR f
wherein R f is selected from the group consisting of C 1 -C 6 (per)fluoroalkyls, C 5 -C 6 cyclic (per)fluoroalkyls, and C 2 -C 6 (per)fluorooxyalkyls.
7 . The method according to claim 1 , wherein said at least one additive is a (per)fluoro-alkylmethylenoxy-vinylether (MOVE) having formula:
CF 2 ═CFOCF 2 OR f
wherein R f is selected from the group consisting of C 1 -C 6 (per)fluoroalkyls, C 5 -C 6 cyclic (per)fluoroalkyls, and C 2 -C 6 (per)fluorooxyalkyls.
8 . The method according to claim 7 , wherein R f is selected from the group consisting of —CF 2 CF 3 (MOVE1), —CF 2 CF 20 CF 3 (MOVE2), or —CF 3 (MOVE3).
9 . The method according to claim 1 , wherein said at least one additive is a (per)fluorinated vinyl derivative having formula:
CF 2 ═CFR f
wherein R f is selected from the group consisting of C 1 -C 6 (per)fluoroalkyls, C 5 -C 6 cyclic (per)fluoroalkyls, and C 2 -C 6 (per)fluorooxyalkyls.
10 . The method according to claim 1 , wherein said at least one additive is a aromatic hydrocarbon substituted with one or more straight or branched alkyl or alkoxy groups and/or halogen atoms.
11 . The method according to claim 10 , wherein said at least one additive is an aromatic hydrocarbon substituted with one or two groups selected from the group consisting of straight or branched alkyl or alkoxy groups and/or halogen atoms.
12 . The method according to claim 10 , wherein said at least one additive is a substituted C 6 aromatic hydrocarbon.
13 . The method according to claim 1 , wherein said at least one additive is in an amount from 0.001 wt. % to 10 wt. %, based on the total weight of the high-molecular-weight PTFE.
14 . The method according to claim 1 , wherein the second step b) is carried out in the presence of an inert gas and/or an oxygen adsorbent.
15 . The method according to claim 1 , wherein the ionizing radiation is selected from the group consisting of electron beams, ultraviolet rays, gamma rays, X-rays, neutron beams and high energy ions.
16 . The method according to claim 1 , wherein said at least one additive is an ether of formula R 1 —O—R 2 , wherein R 1 and R 2 are independently selected from the group consisting of C 3 -C 4 straight or branched aliphatic groups.
17 . The method according to claim 1 , wherein said at least one additive is an aromatic hydrocarbon substituted with one or more C 1 -C 8 alkyl and/or alkoxy groups.
18 . The method according to claim 10 , wherein said at least one additive is a substituted C 6 aromatic hydrocarbon, said C 6 aromatic hydrocarbon being substituted with C 1 alkyl and/or alkoxy groups.
19 . The method according to claim 1 , wherein said at least one additive is in an amount from 0.01 wt. % to 5 wt. %, based on the total weight of the high-molecular-weight PTFE.