Lay down a spoonful of prepared pulp next to a glass of diluted fiber suspension and compare both with a finished sheet of paper. All of them could contain cellulose fibers, but they are in fact completely different things at different steps in the papermaking process. Knowing the difference is helpful, as it makes it easier to understand the rest of the process. Concepts like refining, consistency, drainage, pressing, and drying only make sense if you know what you’re talking about! Pulp is the fibrous material obtained after processing plant material or recycled paper to obtain clean and useable cellulose fibers. Depending on the method of preparation, the pulp may vary in fiber length, quality, color, etc., but at this stage, it is not yet suitable to make a sheet of paper.
Rather, you should consider pulp the raw material, or base material for fibers that goes on to undergo mixing, conditioning, etc. before being fed into the paper machine. Stock is the fibrous suspension used for papermaking. It consists of pulp, water, and, depending on the grade of paper, additional materials such as fillers or size. Stock preparation may involve dilution, refining, blending, screening, and cleaning. Consistency refers to the amount of fiber material present as compared to the total volume of the suspension.
Anyone calling everything wet and containing fibers “pulp” is missing out on a significant aspect of papermaking process since the stock is now ready to be metered into the paper machine. Here’s another way of explaining the difference: Add a process diagram and label where pulp goes into stock preparation, where the prepared stock flows into the headbox, and where water is removed from the stock on the wire to form the web.
What’s happening? Pulp becomes part of a finely tuned suspension, the stock is evenly distributed over the forming fabric, and water leaves while the fibers stay behind. This is very useful because it helps you connect words to what is really happening. Paper is what you get after forming the fibers into a mat and going through further processing. The wet web leaving the forming section contains a lot of water and is not very strong. Presses remove some more water and improve the web structure. The dryer section removes more water and the final properties like smoothness, thickness, etc. may be improved by further post-processing.
Calling the wet suspension “paper” means skipping most of the processing! In addition, these three words help you understand where the problem may lie. Is it in the preparation of the fibers or the refining? Then you probably mean pulp or stock. Are you looking at the uniformity of delivery from the headbox or the drainage on the wire? Then stock and web formation may be more relevant. Is the issue related to the basis weight, thickness, opacity, moisture content, or smoothness? Then you’re dealing with paper. Using the correct word helps you focus on the correct part of the process!
An easy way to check your understanding: Take a single sheet of paper and walk backwards through the process, saying which words apply at which step. Paper comes from a pressed and dried web; the web was formed from stock; the stock was made from pulp, water, and other chemicals. If you can do this correctly, you’ve got a much better grasp of the papermaking process.