(6) Property, plant and equipment, net

As of March 31, 2018 and December 31, 2017, property, plant and equipment consisted of the following:

	March 31,			December 31,
	2018			2017
Property, Plant, and Equipment:
Land use rights	$	12,968,241		$	12,479,814
Building and improvements		102,736,091			98,866,703
Machinery and equipment		123,474,514			118,670,578
Vehicles		616,484			593,265
Construction in progress		38,023,949			36,077,498
Totals		277,819,279			266,687,858
Less: accumulated depreciation and amortization		(84,066,178	)		(77,299,149	)
Property, Plant and Equipment, net	$	193,753,101		$	189,388,709

As of March 31, 2018 and December 31, 2017, land use rights represented two parcel of state-owned lands located in Xushui County of Hebei Province in China, with lease terms of 50 years expiring from 2061 to 2066.

Construction in progress mainly represents payments for the new 15,000 tonnes per year tissue paper manufacturing equipment PM8, the tissue paper workshops and general infrastructure and administrative facilities in the Wei County Industrial Park. The tissue paper development project at the Wei County Industrial Park is expected to be completed in 2018. For the three months ended March 31, 2018 and 2017, the amount of interest capitalized is $nil and $5,164, respectively.

As of March 31, 2018 and December 31, 2017, certain property, plant and equipment of Orient Paper HB with net values of $7,782,238 and $7,963,285, respectively, have been pledged pursuant to a long-term loan from credit union of Orient Paper HB. Land use right of Orient Paper HB with net values of $6,651,641 and $6,437,419 as of March 31, 2018 and December 31, 2017 were pledged for the bank loan from Bank of Industrial & Commercial Bank of China. In addition, plant and equipment of Orient Paper Shengde with net values of $15,440,870 and $nil as of March 31, 2018 and December 31, 2017, respectively, and another land use right with net value of $5,279,211 and $nil as of March 31, 2018 and December 31, 2017 were pledged for the bank loan from Bank of Cangzhou. See “Short-term bank loans ” under Note (7), Loans Payable, for details of the transaction and asset collaterals.

Depreciation and amortization of property, plant and equipment was $3,730,585 and $3,615,359 for the three months ended March 31, 2018 and 2017, respectively.