3913.90 - Other:

This HTS category, 3913.90, encompasses "Other" natural polymers and their modified forms that are not elsewhere specified or included within Chapter 39, and are presented in primary forms. This broad classification applies to a range of materials derived from natural sources, such as alginic acid, but specifically excludes those explicitly enumerated under sibling categories.

While the parent category addresses natural and modified natural polymers generally, 3913.90 serves as a residual category for those not precisely fitting the more specific subheadings. It differentiates itself from its sibling, 3913.10.00.00 (Alginic acid, its salts and esters), by not being limited to alginates. Instead, it captures a wider array of natural polymer derivatives.

The subcategories within 3913.90 provide further specificity. 3913.90.10.00 covers chemical derivatives of natural rubber, a distinct group of modified natural polymers. 3913.90.20 addresses polysaccharides and their derivatives, which are complex carbohydrates with polymeric structures. The remaining 3913.90.50.00 serves as a final residual category for any other natural or modified natural polymers in primary form that do not fall into the preceding subheadings.