(Reuters) - U.S. chemicals producer DowDuPont's DWDP.N disappointing earnings forecast for 2018 overshadowed a strong fourth quarter, which was underpinned by robust demand and higher prices.

Shares of the company, formed by the merger of chemical giants Dow Chemical and DuPont, were down 2.5 percent at $73.56 on Thursday.

DowDuPont said it expected earnings per share to grow in the mid-to-high teens percentage range, implying earnings of $3.90-$4.05. That was below the market consensus of $4.22 per share, according to Cowen and Co analysts.

The forecast assumes higher interest expenses related to some new projects, Chief Executive Edward Breen said on a call with analysts.

The company, however, expects to see strong growth trends in 2018.

“In developed economies in particular, such as the United States, Germany, France, Canada and the U.K., we continue to see strong leading indicators of broad-based growth,” Executive Chairman Andrew Liveris said in the results statement.

The chemicals giant said it raised prices by about 5 percent across markets in the fourth quarter, while volumes - a proxy for demand - rose 6 percent.

Net sales in the quarter were $20.1 billion versus comparable net sales - which the company terms “pro forma” sales - of $17.7 billion a year earlier.

The company also said it was pushing ahead with its plans to split into three separate units, starting with the Materials Science business by the end of the first quarter of 2019. Agriculture and Specialty Products are expected to follow by June 1, 2019.

Currently trading at a market value of about $177 billion, Dow and DuPont completed the $130 billion merger in September.

The merger was welcomed by investors as a way to streamline the companies’ sprawling operations by combining overlapping businesses.

DowDuPont now expects to save $3.3 billion from the merger, slightly more than the $3 billion it had estimated earlier.

The company saw a $1.1 billion benefit from lower U.S corporate taxes in the fourth quarter, but still posted a net loss of $1.2 billion from continuing operations, largely due to merger-related costs.

Adjusted for the tax benefit and other one-time items, the company said it earned 83 cents per share. Wall Street was expecting 67 cents per share, according to Thomson Reuters I/B/E/S.