Opportunities in Wet-End Chemistry: Feature Essay, from Jan. 2002

"R&D Chemicals: How they Impact Papermaking"

Martin A. Hubbe
Dept. Wood & Paper Sci., N.C. State Univ., Box 8005, Raleigh, NC 27695-8005
Citation (public domain): http://www4.ncsu.edu/~hubbe/new

The letters "R and D," when you hear them in a paper mill, may have little to do with the R&D department. Yes, even papermakers eventually benefit from research and development, but their immediate focus is more likely to be retention and drainage. These two words can speak volumes about how a paper machine is running and whether the operation is profitable.

At one time it seemed to make sense to talk about the "R" and the "D" additives separately. The "R" stood for "retention aids," and those words almost always meant very high-molecular-mass copolymers of acrylamide. The "D" stood for stand-alone drainage aids such as alum or polyethylenimine (PEI). But, as experienced papermakers know, acrylamide copolymers can affect dewatering - either positively or negatively. And alum or PEI will affect first-pass retention. The merging of retention and drainage treatments has become more complete as chemical vendors have moved to implement multi-component additives systems to optimize both retention and drainage simultaneously. For example, consider the case where a high-charge cationic polymer is added first, followed by a high-mass flocculant, achieving both retention and drainage improvements to a greater extent than was possible by either of these additives by itself.

Britt Dynamic Drainage/Retention Jar device

Increased first-pass retention - the "R" word - can impact papermaking efficiency in at least three ways. One of these ways is by cutting down on solids losses, an issue that also depends on saveall performance. Another economically important impact of retention-promoting chemicals involves the frequency of downtime for boilouts, both scheduled and unscheduled. Retention chemicals usually help keep deposit-prone materials such as pitch and sizing agents bound to fibers, reducing the chance that they end up in deposits or a spots in the product. Another thing that retention aids can affect is the frequency of web breaks. That's because a high load of fine materials in the white water tends to make the system unstable. Any small shift in process chemistry is likely to cause the fine particles to retain more or less in the sheet, changing the composition of the product. A sudden increase in fines level often means that the sheet momentarily becomes too wet, and it will likely break at an open draw.

Faster drainage or dewatering - the "D" part of "R&D" also can be a factor in paper machine profitability. Many paper machines can be described as "drainage limited." That means that they could be running faster and making more product, but for the limitations of water removal in the forming section. Though most paper machine superintendents welcome any opportunity to make more product, there are other ways that papermakers can benefit from faster drainage induced by chemical treatment. One of these is to increase refining, usually a key strategy in achieving needed strength improvements. Another approach is to reduce headbox solids; under appropriate conditions a lower headbox solids will produce a more uniform, less flocculated product.

The next time you need to approve an expenditure for "R&D," don't be quite sure that the request is coming from Research and Development. Maybe it is the paper machine team wanting to make better use of chemicals. Retention and drainage chemicals have multiple benefits for paper machine operations, and they are usually well worth the investment.

Modified Schopper-Reigler freeness tester


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