UNDERSTANDING WATER RETENTION IN WOOD FIBRE

Researchers at Mpact, one of the leading local paper and plastic packaging manufacturers and recyclers, realised the need to deepen their understanding of the water retention of wood fibres across their paper mills. This important property has been shown to govern certain formation and strength properties of papers. While their laboratory already had the capability for physically analysing fibres and characterising the morphology, they had to find a way to analyse the water retention of the fibres.

To do this, they decided to acquire a Hettich Universal 320 benchtop centrifuge supplied by Labotec that would allow them to measure the Water Retention Value (WRV) of wood fibres specifically and relatively easily.

Fibre characterisation capabilities

The Hettich centrifuge is located at Mpact’s Performance Packaging Innovation Centre in Springs. According to Lead Scientist, Michelle du Preez, this laboratory focuses on the physical testing of paper and paperbased packaging and its function is to support all Mpact operations by providing research, development and technical support services. She added, “the centrifuge is located in the Pulp & Coating section of our laboratory and forms part of our fibre characterisation capabilities. After developing and validating the test method, we now offer it as part of our analytical services to internal and external customers.”

“At the moment, the only test method that has been developed for the centrifuge is for the testing of the water retention value of wood fibres used in the papermaking process. The water retention value is an indication of the extent of fibrillation of the fibre, as well as the swelling ability of the fibre. Both these properties relate to the formation and strength properties of the paper, and hence it provides valuable data that can be used to characterise the raw materials used in our products,” says du Preez.

WRV in accordance with ISO 23714:2007

Normally additional centrifuge sample holders for this value are specially manufactured and therefore expensive, but on account of a new centrifuge adapter with sample holder type A.1 as given in ISO 23714:2007, this part was included as a standard accessory. After developing and validating the test method, the centrifuge allows for straightforward measurement of the WRV as it rises and changes during the course of the manufacturing process. This consequently provides valuable information on the impact of the individual steps in the digestion process on the fibres produced,

Xihluke Mabasa, Research Technologist from Mpact’s Performance Packaging Innovation Centre in Springs working with the Hettich Universal 320 benchtop centrifuge supplied by Labotec. This centrifuge allows him to measure the Water Retention Value (WRV) of wood fibres specifically and relatively easily.

Future prospects and plans T

he Mpact Performance Packaging Innovation Centre supports its three company paper divisions; recycling, paper manufacturing and paper converting. Recycling collects recyclable paper, plastics and liquid cartons to recycle these. Paper manufacturing makes virgin and recycled fibre-based packaging and industrial paper grades (such as containerboard), while paper converting makes printed and unprinted converted corrugated products, including board used to manufacture corrugated packaging, corrugated boxes, cases, trays, point-of-sale displays, cups, lids, bags and trays. Mpact’s aim is focused on closing the loop in plastic and paper packaging through recycling and beneficiation of recyclables through innovation.

According to Michelle du Preez, “our laboratory has extensive paper strength testing capabilities that have been built up over a number of years. Our focus now is to expand on our pulp, coating and print test capabilities.”

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