Synthesis of new high molecular weight phosphorylated chitosans for improving corrosion protection

Abstract

Two grades of chitosan [chitosan 30000 g mol−1 (N-chitosan 30) and 250000 g mol−1 (N-chitosan 250)] were functionalized by the Kabachnik–Fields reaction. To obtain the highest phosphonic ester grafting rate (55% and 40% for the N-chitosan 30 and N-chitosan 250, respectively), the pH must be kept constant during the reaction (pH=5). Then, a partial hydrolysis of the ester functions was carried out in HCl medium to generate phosphonic acid functions up to 25% and 20% for the N-chitosan 30 and N-chitosan 250, respectively. It was shown that the grafting of phosphonic acids on chitosan significantly reduced the dynamic viscosity. Afterwards, electrochemical impedance measurements were performed in an aqueous solution (pH=5) in the presence of either N-chitosans or P-chitosans (3 wt.%). The two native N-chitosans were little adsorbed onto the carbon steel surface and the corrosion protection was low. In contrast, the impedance results in the presence of the 30000 g mol−1 phosphorylated chitosan (P-chitosan 30) evidenced the beneficial effect of grafted phosphonic acid on its adsorption on the steel surface. The lower efficiency of the 250000 g mol−1 (P-chitosan 250) was attributed to its high molecular weight which made difficult the interactions between the phosphonic groups and the metallic surface.

Chitosan: An Overview of Its Properties and Applications

“…For instance, solubility has been improved in water aqueous media by deacetylation, depolymerization, or quaternisation among other processes [ 23 ]. New chitosan activities have been reported after its modification, for example, 6-O-sulphated chitosan promotes neuronal differentiation while phosphorylated chitosan inhibits corrosion [ 24 , 25 ].…”

New bio-based phosphorylated chitosan/alginate protective coatings on aluminum alloy obtained by the LbL technique

“…Native chitosan, high molecular weight (M w ≈ 250,000 g mol −1 , degree of deacetylation: 92%, henceforth called Nchitosan250) and medium molecular weight (M w ≈ 30,000 g mol −1 , degree of deacetylation: 92%, henceforth called Nchitosan30) were purchased from Glentham Life Sciences society. Phosphorylated chitosan from Nchitosan30 (henceforth called Pchitosan30) and from Nchitosan250 (henceforth called Pchitosan250) were synthesized according to our previous study [30]. Sodium alginate (from brown algae, M w = 140,000 g mol −1 ) was purchased from Aldrich.…”

“…Furthermore, the phosphorous-containing molecules or polymers can act as adhesion promoters for different s ubstrates s uch a s a luminum, z inc a nd steel [28,29]. In our previous work, it was shown that the use of chitosan bearing phosphonic acid groups decreased the corrosion rate of a carbon steel by comparison with native chitosan [30]. Some LbL systems, based on phosphorylated chitosan have already been published, aiming at providing new protective coatings for fireproof applications [31].…”

“…In our previous study [30], native chitosan, high molecular weight (M w ≈ 250,000 g mol −1 , called Nchitosan250) and medium molecular weight (M w ≈ 30,000 g mol −1 , called Nchitosan30) were modified by grafting phosphonic acid functions onto primary amines. About 20% of the primary amines were modified for each chitosan.…”

Chitosan: A Versatile Polymer for 21st Century

“…For instance, solubility has been improved in water aqueous media by deacetylation, depolymerisation or quaternisation among other processes [16]. New chitosan activities have been reported after its modification, for example, 6-O-sulfated chitosan promotes neuronal differentiation while phosphorylated chitosan inhibits corrosion [17,18].…”