Cellulose-fiber dispersion polyethylene resin composite material, formed body and pellet using same, production method therefor, and recycling method for cellulose-fiber adhesion polyethylene thin film piece

A cellulose fiber dispersion polyethylene resin composite material, formed by dispersing a cellulose fiber into a polyethylene resin,

• wherein a proportion of the cellulose fiber is 1 part by mass or more and 70 parts by mass or less in a total content of 100 parts by mass of the polyethylene resin and the cellulose fiber,
• wherein the polyethylene resin satisfies a relationship:
• 1.7>half-width (Log(MH/ML))>1.0 in a molecular weight pattern obtained by gel permeation chromatography measurement;
• and
• wherein the composite material has a dispersibility of the cellulose fiber such that a number of mountains having a peak top of 30 μm or more and being convex upward, from a surface of a formed body toward an outside thereof, when counted in all of 10 lines of roughness curves, is less than 20, wherein the following method is used for evaluating the dispersibility of the cellulose fiber within the composite material:
• the composite material is dried by hot air at 80° C. to reduce a moisture content to 0.5% by mass or less;
• the composite material is shaped to the formed body, which is in a sheet form having a dimension of 100 mm×100 mm×1 mm;
• the formed body is immersed into water at 80° C. for 20 days;
• a square having a size of 40 mm×40 mm is drawn in an arbitrary place on a surface of the formed body;
• 9 line segments having a length of 40 mm are drawn inside the square at an interval of 4 mm;
• roughness on an intermediate line between adjacent two line segments is measured under conditions of cut-off value λc=8.0 mm and λs=25.0 μm by using a surface roughness measuring instrument to obtain 10 lines of roughness curves, specified by JIS B 0601 at an evaluation length of 40 mm;
• and
• the number of mountains having a peak top of 30 μm or more and being convex upward, from the surface of the formed body toward an outside thereof, is counted in all of 10 lines of the roughness curves.