(6) Property, plant and equipment, net

As of September 30, 2018 and December 31, 2017, property, plant and equipment consisted of the following:

	September 30,			December 31,
	2018			2017
Property, Plant, and Equipment:
Land use rights	$	11,853,936		$	12,479,814
Building and improvements		93,908,421			98,866,703
Machinery and equipment		112,865,579			118,670,578
Vehicles		596,094			593,265
Construction in progress		35,796,450			36,077,498
Totals		255,020,480			266,687,858
Less: accumulated depreciation and amortization		(83,751,196	)		(77,299,149	)
Property, Plant and Equipment, net	$	171,269,284		$	189,388,709

As of September 30, 2018 and December 31, 2017, land use rights represented two parcel of state-owned lands located in Xushui District 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 the fourth quarter of 2018. For the three months ended September 30, 2018 and 2017, the amount of interest capitalized are $nil. For the nine months ended September 30, 2018 and 2017, the amount of interest capitalized is $nil and $9,761, respectively.

As of September 30, 2018 and December 31, 2017, certain property, plant and equipment of Dongfang Paper with net values of $6,214,258 and $7,963,285, respectively, have been pledged pursuant to a long-term loan from credit union of Dongfang Paper. Land use right of Dongfang Paper with net values of $6,011,133 and $6,437,419 as of September 30, 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 Baoding Shengde with net values of $13,311,236 and $nil as of September 30, 2018 and December 31, 2017, respectively, and another land use right with net value of $4,734,031 and $nil as of September 30, 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 $3,462,703 and $3,729,002 for the three months ended September 30, 2018 and 2017, respectively. Depreciation and amortization of property, plant and equipment was $10,873,536 and $10,928,502 for the nine months ended September 30, 2018 and 2017, respectively.