Alginic acid, its salts and esters

39.13 - Natural polymers (for example, alginic acid) and modified natural polymers (for example, hardened roteins, chemical derivatives of natural rubber), not elsewhere specified or include$ in primary forms. 39 13.10 3913.90 - Alginic acid, its salts and esters - Other The following are some of the principal natural or modified natural polymers of this heading. (1) Alginic acid, its salts and esters Alginic acid, a oly(uronic acid), is extracted from brown algae Phaeophyta) by maceration in an aL1ine solution. ~t may be produced by precipitating t e extract with a mineral acid or by treating the extract to obtain an impure calcium alginate which on treatment with a mineral acid is transformed into alginic acid of high purity. Alginic acid is insoluble in water but its ammonium and alkali metal salts dissolve readily in cold water to form viscous solutions. The roperty of forming viscous solutions varies with the origin and degree of purit of the a ginates. Water-soluble a1 ates are used as thickeners, stabilisers, gelling and ilm-forming agents in, for example, t e pharmaceutical, food, textile and paper industries. P r Y These roducts ma contain preservatives (e.g., sodium benzoate) and be standardised by i of ge ling agents (e.g., calcium salts), retarders (e.g., phosphates, citrates), the ad$tion accelerators (e ., organic acids), and regulators (e ., sucrose, urea). Any such additions should not ren er the product particularly suitable or specific use rather than for general use. f S Among the esters is propylene glycol alginate which is used in foodstuffs, etc. (2) Hardened proteins Proteins are nitrogenous compounds of very high molecular wei ht of vegetable or animal origin. They are suitable for processin into plastics. The h e a L covers only proteins whch have been chemically processe to harden them. Only a ew are of commercial importance. d r Hardened proteins are general1 in the form of blocks of regular shape, sheets, rods or tubes. In these forms they are excluded $om this heading (generally heading 39.16,39.17,39.20 or 39.21). (3) Chemical derivatives of natural rubber Natural rubber, which is a high polymer, forms, on chemical treatment, certain substances having the characteristic of plasticity. These include : (a) Chlorinated rubber. This is usually produced in the form of small white mules. It is used in the preparation of aints and varnishes which after application orrn a film resistant to atmospheric and c emical deterioration. F, P (b) Rubber hydrochloride. Generally used in packaging, and, when plasticised, for protective clothing. (c) Oxidised rubber, obtained by oxidising heated rubber in the presence of a catalyst. It is a resinous material used in certain types of varnishes. (d) Cyclised rubber, obtained by treating rubber with, e.g., sulphuric, chlorosulphuric or chlorostannic acids. This gives a range of products of varying hardness, used a s a basis in the preparation of ants, for waterproof coatings, and to some extent in the manufacture of moulde products. i' (4) Dextran, glycogen (" animal starch ") and chitin and plastics produced from lignin This heading also includes isolated amylopectin and isolated amylose obtained by the fractionation of starch. A For the classification of olymers (including copolymers chemically modified polymers and polymer blends, see the eneral Explanatory Note to this hapter. cP The heading excludes : (a) Unmodified natural resins (heading 13.01). (b) Etherified or esterified endosperm flour of locust beans or guar seeds (beading 13.02). (c) Linoxyn (heading 15.18). (d) Heparin (heading 30.01). (e) Starch ethers and esters (heading 35.05). ( f ) Rosin, resin acids and their derivatives (including ester gums and run gums) (heading 38.06).