In both mechanical and Kraft pulp mills wood chip is required to produce pulp.

 

Wood chip is produced both on site and externally. Pulp mills can produce their own wood chip using a chipping mill. This is either a drum or disk chipper in which debarked logs (logs with the bark peeled off) are fed into it to produce chip. The types of logs used are broken down into

 

• Thinnings

  • Produced whilst a forest is thinned out, these logs/ stems are too small to be processed by sawmills.

• Top Logs

  • The narrow part of the stem of a tree which aren't wide enough to be processed in saw mills.

• Pulp Logs

  • These are logs which have a defect (such as too much bow) and aren’t viable for use in saw mills.

 

Theses logs are transported to site using logging trucks. And are harvested from private plantations that are either owned by the company or a forestry management company such as Timberlands. See:

 

http://www.tll.co.nz/

 

The other source of chip is from sawmills. When a log is processed a lot of chip is produced while chipping off rounded edges to make square boards. Sawmills either use this chip as fuel in boilers or they sell it on to pulp mills. The chip is stored in large overhead bins or silos, which truck drivers can park underneath to dump chip into the trailer units. Sawmills have very strict contracts regarding the quality of chip they produce and have to ensure it’s free of any impurities such as rubbish. 

 

The quality of the chip is affected by many factors:

 

• Species of the tree.

• Age of the tree.

• Part of the tree which the chip was produced from.

• Location that the tree was grown.

 

The quality of chip directly affects the quality of the pulp which is measured in its strength and optical attributes. Pulp mills in New Zealand use Radiata pine a softwood which is grown in abundance (approximately 90% of plantation forestry is Radiata pine (Ministry for Primary Industries, 2014)) due to its fast growth rate in this climate/ environment and the fact it still strong enough that sawn Radiata meets structural timber grades. In Carter Holt Harvey’s Kraft pulp mills they have a ratio of 1:20 eucalyptus chip to Radiata pine chip (R. Ennis, Graduate Process Engineer Carter Holt Harvey Kinleith, personal communication, July 30, 2015). The eucalyptus is hardwood and is a replacement to the native Tawa that used to be used as a supplement to modify the resultant pulp properties.