[' ', 'MAKE', 'oe', '.', 'oy', '\\', 'the', 'die', 'increases', 'to', 'the', 'point', 'that', 'the', 'surface', 'of', 'the', 'ex-', 'truded', 'product', 'becomes', 'porous', 'and', 'rough,', 'which', 'results', 'in', 'a', 'less', 'than', 'desirable', 'degree', 'of', 'foaming.', 'At', 'water', 'contents', 'in', 'excess', 'of', 'about', '50', 'wt.', '%,', 'without', 'alteration', 'of', 'tempera-', 'ture,', 'insufficient', 'energy', 'is', 'supplied', 'to', 'the', 'formulation', 'to', 'generate', 'foam', 'formation', 'as', 'the', 'product', 'exits', 'the', 'die.', '|', 'Optionally,', 'in', 'step', '(a),', 'in', 'step', '(b)', 'or', 'in', 'step', '(c),', 'a', 'foaming', 'agent', 'may', 'be', 'added', 'to', 'the', 'blend.', 'The', 'foaming', 'agent', 'is', 'preferably', 'selected', 'from', 'the', 'group', 'con-', 'sisting', 'of', 'air,', 'nitrogen,', 'carbon', 'dioxide,', 'ammonium', 'carbo-', 'nate,', 'ammonium', 'carbamate,', 'an', 'azide,', 'a', 'hydrazide,', 'pentane,', 'hexane,', 'heptane,', 'a', 'halogenated', 'fluorocarbon,', 'pyrrole,', 'acetone,', 'ethanol,', 'a', 'peroxide,', 'and', 'azodicarbonamide.', 'Some', 'of', 'these', 'foaming', 'agents', 'require', 'the', 'addition', 'of', 'an', 'acid.', 'In', 'step', '(c),', 'the', 'wet', 'blend', 'is', 'fed', 'into', 'an', 'extruder', 'and', 'processed', 'as', 'set', 'forth', 'in', 'greater', 'detail', 'below.', 'The', 'wet', 'blend', 'is', 'extruded', 'under', 'extrusion', 'conditions', 'o£', 'tempera-', 'ture', 'and', 'pressure', 'such', 'that', 'as', 'the', 'wet', 'blend', 'is', 'extruded,', 'the', 'moisture', 'in', 'the', 'blend', 'is', 'converted', 'to', 'steam,', 'thereby', 'foaming', 'the', 'article,', 'Preferred', 'extruders', 'include', 'single', 'screw', 'cooking', 'extruders,', 'which', 'are', 'high', 'temperature/short', 'time', 'extruders', 'that', 'are', 'essentially', 'Archimedean', 'pumps', 'and', 'which', 'have', 'heretofore', 'been', 'employed', 'in', 'the', 'food', 'industry,', 'hydraulic', 'piston', 'extruders,', 'ram', 'extruders,', 'and', 'extruders', 'employing', 'an', 'extrusion', 'chamber', 'consisting', 'of', 'a', 'male', 'auger', 'and', 'a', 'sleeve', 'which', 'incorporates', 'a', 'female', 'auger,', 'a', 'spacer', 'ving,', 'and', 'a', 'face', 'plate', '(or', 'die)', 'to', 'shape', 'the', 'foamed', 'product.', 'It', 'is', 'important', 'that', 'the', 'tobacco', 'particles,', 'the', 'cellulose', 'binder,.', 'and', 'any', 'preferred', 'additional', 'ingredients', 'be', 'mixed', 'to', 'form', 'a', 'homogeneous', 'mixture', 'prior', 'to', 'introduction', 'into', 'the', 'feeding', 'bin', 'of', 'the', 'extruder.', '13', ' ', ' ', ' ', '28840b9202']