Pliant Corp., an Illinois-based manufacturer of packaging projects, is closing its Massachusetts plant and will lay off 103 people. The company filed details of its plans with the state in May, and began reducing its workforce at the South Deerfield, Mass., facility recently. Pliant said the company's Massachusetts employees would be laid off in stages over as long as seven months. Pliant said it would negotiate with the Union Electrical, Radio & Machine Workers of America, which represents the affected employees, over the effects of the plant closing. Pliant makes packaging for personal care, medical, food, industrial and agricultural markets.