Method for preparation of decontaminated natural rubber, that comprises a decontamination step in which wet natural rubber coagulum with a humidity level greater than 12% by weight passes through a system comprising an extruder and a filter installed at the extruder outlet, the extruder comprising a grooved sheath , a screw arranged in the sheath and comprising a hub and a thread which extends radially outwardly relative to the hub, a grooved sheath having an axially symmetrical structure comprising in its thickness grooves opening on the inner surface of the sheath , each groove comprising - a bottom face delimited by two bottom ridges , - two side faces extending towards the inside from the bottom face , each being delimited by a bottom ridge and a ridge intersecting the inner surface of the sheath , the process being characterized in that the sheath is such that, in any plane perpendicular to the axis of the sheath , R expressed in mm being the distance between the sheath centre and the inner surface of the sheath : a. the ratio (total length of groove openings expressed in mm )/(2πR), designated A, is at least equal to 0.25 and at most equal to 0.9; b. the ratio (number of grooves/2R), designated B, is greater than or equal to 0.1; c. the ratio (depth of grooves expressed in mm)/ , designated C, is greater than 0.02, and d. the plane passing through the two bottom ridges forming, with each plane passing through a bottom ridge and an intersection ridge delimiting a side face , an angle δ at least equal to 60° and at most equal to 90°. the extruder comprising a grooved sheath , a screw arranged in the sheath and comprising a hub and a thread which extends radially outwardly relative to the hub, a grooved sheath having an axially symmetrical structure comprising in its thickness grooves opening on the inner surface of the sheath , each groove comprising - a bottom face delimited by two bottom ridges , - two side faces extending towards the inside from the bottom face , each being delimited by a bottom ridge and a ridge intersecting the inner surface of the sheath , - a bottom face delimited by two bottom ridges , - two side faces extending towards the inside from the bottom face , each being delimited by a bottom ridge and a ridge intersecting the inner surface of the sheath , the process being characterized in that the sheath is such that, in any plane perpendicular to the axis of the sheath , R expressed in mm being the distance between the sheath centre and the inner surface of the sheath : a. the ratio (total length of groove openings expressed in mm )/(2πR), designated A, is at least equal to 0.25 and at most equal to 0.9; b. the ratio (number of grooves/2R), designated B, is greater than or equal to 0.1; c. the ratio (depth of grooves expressed in mm)/ , designated C, is greater than 0.02, and d. the plane passing through the two bottom ridges forming, with each plane passing through a bottom ridge and an intersection ridge delimiting a side face , an angle δ at least equal to 60° and at most equal to 90°. a. the ratio (total length of groove openings expressed in mm )/(2πR), designated A, is at least equal to 0.25 and at most equal to 0.9; b. the ratio (number of grooves/2R), designated B, is greater than or equal to 0.1; c. the ratio (depth of grooves expressed in mm)/ , designated C, is greater than 0.02, and d. the plane passing through the two bottom ridges forming, with each plane passing through a bottom ridge and an intersection ridge delimiting a side face , an angle δ at least equal to 60° and at most equal to 90°. <EOS>