(6) Property, plant and equipment, net

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

	June 30,			December 31,
	2018			2017
Property, Plant, and Equipment:
Land use rights	$	12,324,396		$	12,479,814
Building and improvements		97,635,464			98,866,703
Machinery and equipment		117,344,995			118,670,578
Vehicles		619,752			593,265
Construction in progress		36,617,247			36,077,498
Totals		264,541,854			266,687,858
Less: accumulated depreciation and amortization		(83,484,424	)		(77,299,149	)
Property, Plant and Equipment, net	$	181,057,430		$	189,388,709

As of June 30, 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 June 30, 2018 and 2017, the amount of interest capitalized is $nil and $4,499, respectively. For the six months ended June 30, 2018 and 2017, the amount of interest capitalized is $nil and $9,663, respectively.

As of June 30, 2018 and December 31, 2017, certain property, plant and equipment of Dongfang Paper with net values of $6,927,618 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 $6,285,552 and $6,437,419 as of June 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 $15,001,701 and $nil as of June 30, 2018 and December 31, 2017, respectively, and another land use right with net value of $4,991,336 and $nil as of June 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 $3,680,248 and $3,584,141 for the three months ended June 30, 2018 and 2017, respectively. Depreciation and amortization of property, plant and equipment was $7,410,833 and $7,199,500 for the six months ended June 30, 2018 and 2017, respectively.