When used as wet end additives, small amounts of derivatized guar, as well as at least one other gum, seem to have a remarkably beneficial effect on both the papermaking process and the physical properties of the final product. We begin by providing experimental data, and conclude by offering a conceptual hypothesis to explain the mechanisms underlying the synergism, and by providing a recommendation.

The control experiment 234 uses 40% fiber and 30% coated broke, to which was added 30%PCC plus polyDADMAC cationic scavenger, AKD internal size, and 0.5% cationic starch with a silica/anionic polymer retention system.

Experiment 239 replaces 5% (only 0.5 lb.) of the cationic starch with a cationic guar gum known as Rhodia CP-13. Experiment 240 replaces 5% of the cationic starch with a gum from a different plant species than guar, which is not derivatized.

All of our benchmark experiments, including this short series, are conducted at or very close to the optimum zeta potential for that particular process. They are also repeated. We are thereby assured that the results are highly reproducible. Following is the data.

We have concluded that cationic guar gum is distinguished by the following characteristics: 1. The cationic "derivatization" which makes it attractive to negatively charged particles, and 2. A molecular structure very close to that of cellulose which provides a strong attraction to fines and fibers, as well as to starch.

Use of cationic guar gum in experiment 239 results in a large increase in drainage, which we invariably observe. We suggest that it derives from the cationic guar gum attaching itself to the fines and fibers because of its structural similarity, and then participating fully in the microparticulate flocculation because of its cationic charge. The result is an unusually extensive and effective microflocculation of the fines and fibers.

The greatly increased sizing and Scott Bond are most significant, in fact counter-intuitive, given a 5% higher sheet ash level. We suggest that they both derive from the similarity of that guar gum molecular structure to that of starch, which greatly enhances starch retention, and therefore increases strength. The HST sizing numbers are higher because Hercules emulsifies AKD in starch, thereby cleverly increasing AKD retention.

The underivatized gum is not as attractive to PCC and therefore does not improve sheet ash, as does the cationic guar gum. Similarly, the lack of cationicity reduces microflocculation and impairs drainage, in comparison with the cationic guar gum. However, Scott Bond is increased, and sizing is so much improved over the control it suggests that this particular molecule is even closer to that of cellulose and/or starch, and therefore more effective than the guar structure.

Guar gum and its homologues are much under-appreciated and under-used in wet end chemistry. We are reminded of our late dear friend and highly respected colleague, Fritz Werdouschegg, and his seminal pioneering work in this area. Fritz was prescient, especially in his work with recycle systems. We recommend that the technology be evaluated in many paper and board making processes, and certainly those which contain starch, internal size emulsified in starch, or a microparticle system.

John G. Penniman,