[away3d] Change material on .obj

[mika]

Hi list

I'm starting with away3d and I find mysel blocked at the beginning og my
project.

I can load an obj, with its associated texture :

protected override function _createScene():void
        {
            loader = new Loader3D();
            loader.addOnSuccess(_onSuccess);

            loader.loadGeometry("ballon_HiRes_ok1.obj", obj);
        }

no problem, if i set another material on load, no problem :

        protected function _onSuccess(e:Loader3DEvent):void
        {
            trace('Finished Loading: ' + e.currentTarget)
             mesh = loader.handle as Mesh;
             mesh.scale(25)
             mesh.y = 0;
             mesh.bothsides = false
             mesh.material = _wireMat
            _view.scene.addChild(mesh);
        }

But, if I try to change the material after the obj is added to scene, no
success :

        public function changeMaterial(texture:Bitmap)
        {
            var newMat:BitmapMaterial = new
BitmapMaterial(texture.bitmapData)
            obj.material = newMat
        }

I have try to access the material like this :

mesh.materialLibrary.getMaterial("1_uv-test-position.jpg").material =
_wireMat

but without any success.

Help would be greatly appreciated