Polymer Degradation and Stability (v.92, #3)

Calendar (I-II).

The behaviour of the acrylic–silicone mixture commonly known as Bologna Cocktail, composed of commercial acrylic polymer Paraloid B72 and the silicon-based product, Dri Film 104, extensively employed as stone preservative for monuments in the last thirty years, has been tested on specimens appropriately prepared and submitted to ageing simulating reliable outdoor environment. After chemical characterization, the acrylic–silicone mixture was applied as thin film on slides, as thick film on Petri dishes and on marble by brush or by absorption; the resulting samples were artificially aged by light and saline solution. The chemical modifications were evaluated by FT-IR, NMR and SEC determinations, while preservative properties were tested by removability tests, ultrasonic and colorimetric measurements. The mixture consists of two immiscible phases and the two components have distinctive chemical behaviours, leading – after ageing – to irreversible molecular modifications and loss of conservative properties. The deterioration processes identified through laboratory simulation have been also verified on treated marble surfaces of two Venetian case studies.
Keywords: Acrylic–silicone mixture; Stone conservation; Photo-oxidative and saline solution ageing; Acrylic carboxylate salts;

Pulsed IR laser ablation of poly(vinyl phenyl ketone) results in the formation of CO, C1–C4 hydrocarbons, benzene, styrene and phenylacetylene and affords deposition of polymeric films that were examined by EDX-SEM, FTIR, UV and NMR spectroscopies and gel-permeation chromatography. It is revealed that the structure of the films is affected by laser fluence and their M w distribution is almost identical to that of poly(vinyl phenyl ketone). The formation of the products is accounted for by cleavages of both polymer backbone and pendant group. Conventional heating of poly(vinyl phenyl ketone) yields CO, formaldehyde, methanol and benzene as major volatile products and affords a solid fraction showing substantial fragmentation of the polymer. The different degradation products from both processes are ascribed to different modes of heating and to the wall effect.
Keywords: Poly(vinyl phenyl ketone); Laser degradation; Laser ablation; Ablative deposition; Laser-induced polymer films; Conventional degradation;

Synergetic degradation of chitosan with gamma radiation and hydrogen peroxide by Bin Kang; Yao-dong Dai; Hai-qian Zhang; Da Chen (359-362).
Chitosan samples were irradiated by 60Co γ-rays in the presence of hydrogen peroxide with radiation dose from 10 kGy to 100 kGy. The degradation was monitored by gel permeation chromatography (GPC), revealing the existence of a synergetic effect on the degradation. Structures of the degraded products were characterized with Fourier-transform infrared spectra (FT-IR), ultraviolet–visible spectral (UV–vis) analysis, and X-ray diffraction (XRD). Results showed that the crystallinity of chitosan decreases with degradation, and the crystalline state of water-soluble chitosan is entirely different from that of water-insoluble chitosan. An elemental analysis method was employed to investigate changes in the element content of chitosan after degradation. Mechanism of chitosan radiation degradation with and without hydrogen peroxide was also discussed.
Keywords: Chitosan; Degradation; Synergetic effect; Gamma radiation; Hydrogen peroxide;

N-Methylol dimethylphosphonopropionamide (MDPA) is one of the most commonly used durable flame retardant agents for cotton. In our previous research, we developed a new flame retardant finishing system based on a hydroxy-functional organophosphorus oligomer (HFPO) and bonding agents, such as dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM). In this research, we compared the flame resistant performance as well as physical properties of the cotton fabric treated with these two flame retardant finishing systems. The cotton fabric treated with MDPA/TMM has a higher initial limiting oxygen index (LOI) than that of the fabric treated with HFPO/TMM due to higher nitrogen content in the system. The LOI of the cotton fabric treated with the HFPO and MDPA systems becomes identical when the treated fabric contains equal amount of phosphorus and nitrogen. The MDPA/TMM shows higher laundering durability on cotton than HFPO/TMM system. The fabric treated with HFPO/TMM and MDPA/TMM has low wrinkle resistance and low strength loss whereas the fabric stiffness significantly increases when the TMM concentration is increased.
Keywords: Cellulose; Cotton; Flame retardant finishing; Trimethylolmelamine; Organophosphorus chemicals;

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites by Orietta Monticelli; Zenfira Musina; Alberto Frache; Federica Bellucci; Giovanni Camino; Saverio Russo (370-378).
Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B® and Nanofil 784®, and a sodium MMT (Cloisite Na®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis–gas–mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes –OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.
Keywords: PA6; Nanocomposites; Layered silicates; Compatibilizer degradation;

Study on permeation behavior and chemical degradation of PA66 in acid solution by Abastari; Tetsuya Sakai; Hideki Sembokuya; Masatoshi Kubouchi; Ken Tsuda (379-388).
In many polymers under corrosive liquids, degradation followed after permeation of environmental solution for a long period. The permeation rate of environmental solution, in many cases, is very low in corrosion-resistant polymeric materials. Therefore, the observation of the permeation of environmental solution and degradation of polymeric materials are very difficult in practical application. A simulation of permeation of solution is required in order to understand the permeation behavior of environmental solution and polymer degradation. A detailed analysis of the permeation behavior of solution accompanied by chemical reaction is important to study for improving the lifetime of polymers. Polyamide 66 (PA66) and sulfuric acid solution were used to investigate the quantitative study of permeation of environmental solution and its relation to degradation of polymeric materials. Correlation between diffusion process and degradation of PA66 related to the decrease of weight average molecular weight was defined. The diffusion rate of sulfuric acid solution was found to increase by decreasing weight average molecular weight of PA66 due to the established chain scission by hydrolysis reaction. The permeation of sulfuric acid solution that affected the decomposition reaction was modeled and quantitative evaluation of permeation of sulfuric acid was established.
Keywords: Diffusion; Molecular weight; Polyamide; Chemical degradation; Sulfuric acid;

Synthesis, characterization and in vitro degradation of a novel degradable poly((1,2-propanediol-sebacate)-citrate) bioelastomer by Lijuan Lei; Tao Ding; Rui Shi; Quanyong Liu; Liqun Zhang; Dafu Chen; Wei Tian (389-396).
Degradable bioelastomers represent a useful class of biomaterials. In this paper, a novel biodegradable network of elastomeric polyesters, poly((1,2-propanediol-sebacate)-citrate) (PPSC), was synthesized by condensation of 1,2-propanediol, sebacic acid and citric acid without any catalyst. An oligomeric diol of 1,2-propanediol-sebacate was first synthesized by carrying out a controlled condensation reaction between 1,2-propanediol and sebacic acid, and then a pre-polymer was synthesized by condensation of the diol and citric acid, whereat the pre-polymer was post-polymerized and simultaneously crosslinked in mold at 120 °C. A series of PPSC polymers were prepared at different post-polymerization times and different monomers' ratio. T g confirms that PPSC is totally amorphous at 37 °C. The mechanical properties of PPSC testified that the new polymers are typical elastomers with low hardness and large elongation. The different post-polymerization times and monomers' ratio had strong influence on the degradation rates and mechanical performances. The material was expected to be useful for drug controlled delivery, tissue engineering scaffold and other biomedical applications.
Keywords: Poly((1,2-propanediol-sebacate)-citrate) (PPSC); Bioelastomer; Water uptake; In vitro degradation;

Photodegradation of bisphenol A polycarbonate by Marjolein Diepens; Pieter Gijsman (397-406).
When bisphenol A polycarbonate is subjected to weathering conditions this polymer shows two different degradation mechanisms depending on the used irradiation wavelengths, i.e. photo-oxidation and photo-Fries rearrangement. The relative importance of these mechanisms in outdoor exposure conditions is still unknown. In this study bisphenol A polycarbonate is exposed to simulated weathering conditions. Different analysing techniques show that photo-oxidation is the most dominant degradation reaction. However, fluorescence spectroscopy shows that small amounts of photo-Fries rearrangement products are formed. With model compounds blended in polypropylene it is shown that the photo-Fries reaction increases the photo-oxidation rate, thus in PP the photo-Fries reaction can proceed through radical intermediates. However, this is not the case in PC, ageing at condition causing an increased photo-Fries reaction rate did not result in a higher oxidation rate. This implies that in PC the photo-Fries reaction does not initiate its oxidation and thus does not proceed through radicals.
Keywords: Bisphenol A polycarbonate; Photodegradation; Photo-Fries; Photo-oxidation; FT-IR; UV spectroscopy;

New unsaturated polyesters as injectable drug carriers by Wen-xun Guo; Zong-li Shi; Kui Liang; Yan-li Liu; Xian-hong Chen; Wei Li (407-413).
New unsaturated polyesters of poly(fumaric acid–glycol–sebacic acid) copolymers and poly(maleic anhydride–glycol–sebacic acid) copolymers were prepared by melt polycondensation of the corresponding mixed monomers: sebacic anhydride, fumaric acid or maleic anhydride and glycol. Methyl-methacrylate (MMA) was used as crosslinker and dimer acid was used as thinner. In vitro studies showed that those copolymers are degradable in phosphate buffer at 37 °C and poly(fumaric acid–glycol–sebacic acid) has proper drug release rate as drug carriers. The biocompatibility of poly(fumaric acid–glycol–sebacic acid) copolymers under mice skin was also evaluated; macroscopic observation and microscopic analysis demonstrated that the copolymer is biocompatible and well tolerated in vivo. The injected poly(fumaric acid–glycol–sebacic acid) [molar ratio M fumaric acid:M glycol:M sebacic acid  = 1.75:2.20:0.25] containing 5% adriamycin hydrochloride (ADM) in the mice bearing Sarcoma-180 tumor exhibited a good antitumor efficacy. The volume doubling time (VDT) (18 ± 2.5 days) of the tumor growth by this treatment was longer than that (7 ± 0.9 days) by the subcutaneous injection of ADM.
Keywords: Unsaturated polyester; Copolymer; Drug release; Adriamycin hydrochloride; Antitumor efficacy;

Mössbauer, NMR and ATR-FTIR spectroscopic investigation of degradation in RTV siloxane foams by Andrea Labouriau; Jonathan D. Cox; Jon R. Schoonover; Brian M. Patterson; George J. Havrilla; Thomas Stephens; Dean Taylor (414-424).
The combination of experimental techniques allowed for a comprehensive study of aging processes occurring in RTV siloxane foams. 119Sn Mössbauer spectroscopy demonstrated that tin residues are composed of Sn(II) and Sn(IV) species. The 27-year-old foams showed only Sn(IV) species with a quadrupole-splitting parameter larger than that observed for SnO2. Solid-state 29Si NMR differentiated between the various functional linkages in the foams, and showed no significant change of the di- to trifunctional linkage ratios. High-resolution NMR, on solvent extract of foams, showed the presence of water, catalyst, plasticizer, and some silicone oligomers. ATR-FTIR demonstrated changes near the surface of the foam when aged with water and with the presence of the tin catalyst. Gamma irradiation at a low dose had little effect on compression sets. The main changes observed for artificially aged and aged in service foams were related to the presence of the tin catalyst.
Keywords: Siloxane foams; Degradation; Tin octoate; Mössbauer; NMR; ATR-FTIR;

Catalytic charring–volatilization competition in organoclay nanocomposites by F. Bellucci; G. Camino; A. Frache; A. Sarra (425-436).
The thermal behaviour of organoclays, and especially their organic treatment, is an important issue in polymer nanocomposite preparation and their fire retardant properties. The thermal behaviour of the organomodifier is strongly affected by the different composition parameters of the clays. Thus the thermal degradation, in inert and in oxidative atmosphere, of natural montmorillonite and synthetic fluorohectorite both exchanged with polar and non-polar organomodifiers was studied using a combined thermogravimetry/Fourier transform infrared and a flash pyrolysis GC–MS system. Decomposition and charring mechanisms of the organic molecules in the clays are proposed for each kind of clay and a relationship between the composition of the clays and the kinetics of the decomposition reactions is found. Furthermore, it is shown that the charring–volatilization competition on heating organoclays in the presence of oxygen depends on the structure of the clay, the confined or unconfined position of the organic molecules and their polarity.
Keywords: Organoclays; Thermal degradation; Catalytic charring; Flame retardancy;

Oxidative degradation is a well-known problem for UHMWPE used in prostheses. The aim of the present study has been to find suitable techniques to study the spatial distribution of this oxidation in 8 retrieved acetabular cups. The techniques used were visual examination using an optical microscope and computer scanner, FTIR mapping, imaging chemiluminescence, and staining with SO2 and HCl. The staining technique is based on a previous study which showed that by treating oxidized UHMWPE with SO2 followed by heat treatment, the hydroperoxides present in the sample react with the SO2 and discolor the sample. The intensity of this discoloring is, at low levels of oxidation, proportional to the amount of hydroperoxides and accordingly to the level of the oxidation. The same study also showed that staining a sample with hot HCl resulted in a brown discoloration which was proportional to the amount of carbonyls. It was found that the staining techniques do not give as much information about the chemical and physical changes in the material as FTIR mapping but have a great advantage in better spatial resolution of the oxidation and are also much quicker and easier to use. Imaging chemiluminescence turned out not to be a suitable method to use, compared to the other two, since it gives less information and is more difficult to interpret.When interpreting the results from the different techniques used, it was found that all cups showed the typical oxidation behavior of gamma sterilized UHMWPE. All cups but one showed substantial wear of the articulating surface but very little backside wear. Examination of the oxidation and whitening profile suggests that at least some of the oxidation must have occurred in vivo.
Keywords: UHMWPE; Polyethylene; Acetabular cup; Oxidation; FTIR; SO2;

Treating a sample of oxidised ultra-high molecular weight polyethylene (UHMWPE) with SO2 will cause a reaction between SO2 and hydroperoxides in the sample, forming a hydrosulphate group. During subsequent heat treatment the hydrosulphate group will leave as sulphuric acid, and a double bond will form in the polymer chain. During this step the sample turns brown. This browning has previously been used to determine the spatial distribution of oxidation in PP. The aim of this work was to apply this also to UHMWPE and to determine what causes the browning and how well it corresponds to the true distribution and concentration of hydroperoxides. The possible future use of the technique to determine the spatial distribution of oxidation in UHMWPE has also been evaluated.The true nature of the browning has been difficult to establish, but it seems to originate from a charge transfer complex between the double bonds and the sulphuric acid. A similar type of coloration develops in oxidised UHMWPE, when it is treated with hot hydrochloric acid. However, in that case the coloration is proportional to the carbonyl concentration and has been concluded to originate from the oxonium ion formed by protonation of ketones. The coloration of both SO2/heat-treated samples and samples treated with hot hydrochloric acid can be used to give a qualitative picture of the spatial distribution of oxidation in UHMWPE. The techniques have been applied to study the heterogeneous oxidation in badly consolidated UHMWPE. It was found that the very good spatial resolution gave information about the heterogeneous oxidation that is not possible to obtain when using other techniques, such as FTIR mapping and imaging chemiluminescence.
Keywords: Oxidation; UHMWPE, ultra-high molecular weight polyethylene; Hydroperoxides; SO2, sulphur dioxide; Hydrochloric acid, HCl; Double bonds;

Cross-linking assessment after accelerated ageing of ethylene propylene diene monomer rubber by N.S. Tomer; F. Delor-Jestin; R.P. Singh; J. Lacoste (457-463).
The ageing of filled and cross-linked ethylene propylene diene elastomer (EPDM) has been studied under accelerated UV irradiation (λ  ≥ 290 nm) at 60 °C, thermal ageing at 100 °C and in nitric acid vapours for different time intervals. Hardness measurements were performed. DSC-thermoporosimetry was used to estimate the mesh size distribution and cross-linking densities for each ageing. The development of functional groups was monitored by ATR spectroscopy. An increase in oxidation with exposure time after the different types of ageing was observed. The thermal stability of EPDM was assessed by TGA and evolved volatile gases were identified using FTIR spectroscopy.
Keywords: EPDM; Ageing; Thermal analysis; Thermoporosimetry; Oxidation;

A series of biodegradable polyesters were synthesized from dicarboxylic acids and 1,3-propanediol catalyzed by transestrification polycondensation reaction in the bulk. The structure, average molecular weights and physical properties of the resulting aliphatic polyesters were characterized by 1H NMR, FT-IR, solution viscosity, GPC, DSC and TGA. Homopolyesters show higher degree of crystallinity, melting and thermal stability in comparison to copolyesters. The biodegradability of the polyesters was determined by monitoring the normalized weight loss of polyester films with time in phosphate buffer (pH 7.2) without and with Rhizopus delemar lipase at 37 °C. The rate of enzymatic degradation of homopolyesters follows the path PPSu > PPAd > PPSe. PPSe did not show significant weight loss in presence of enzyme which may be due to its highest degree of crystallinity and melting point compared to the PPSu, PPAd and copolyesters. In the soil burial degradation polyester sample showed severe surface degradation by the attack of microorganism.
Keywords: Biodegradable polymers; Aliphatic polyesters; Transestrification; Enzymatic degradation; Rhizopus delemar lipase;

Polyurethane networks based on castor oil (CO) as a renewable resource polyol and poly(ethylene glycol) (PEG) with tunable biodegradation rates as potential candidates for biomedical implants and tissue engineering were synthesized through the reaction of epoxy-terminated polyurethane prepolymers (EPUs) with 1,6-hexamethylene diamine curing agent. EPUs themselves were prepared from reaction of glycidol and isocyanate terminated polyurethane prepolymers made from CO or PEG and 1,6-hexamethylene diisocyanate. All of the polymers were characterized by conventional methods, and their physical, mechanical and viscoelastic properties were studied. The results showed that the degradation rate and mechanical properties of final products could be controlled by the ratio of PEG or CO based EPUs in the final products. Increasing the PEG based EPU content caused an increase in hydrolytic degradation rate and mechanical properties. Evaluation of the L-929 fibroblast cells' interaction with prepared polymeric films showed nontoxic behavior and good cytocompatibility.
Keywords: Polyurethanes; Biodegradation; Biocompatibility; Renewable resource;

A study on the Lewis acids-type transition metal chloride (FeCl3) catalyzing carbonization based on acrylonitrile–butadiene–styrene copolymer (ABS)/organophilic montmorillonite (OMT) nanocomposites has been achieved. The results of XRD, TEM and HREM experiments show the formation of intercalated structure. The thermal stability of the nanocomposites slightly decreases, but the char residue remarkably increases compared with pure ABS. Meanwhile, it is found that the loading of FeCl3 leads to crosslinking of ABS, promotes the charred residue yield and catalytic graphitization effect. The structure and morphology (XRD, HREM, SAED and LSR) of the purified char residue approve further the presence of graphite sheets. The possible catalyzing carbonization mechanism is composed of three prominent aspects. The first is the catalyzing effect of FeCl3 promoting the crosslinking of polymer. The second is the Hofmann degradation of OMT, whose degraded products have opposite role in promoting crosslinking reactions and the last is the nano-dispersed clay layers. The gas barrier properties of clay stop or reduce the release of the pyrolytic products, which have been dehydrogenated for more time and aromatized to form char.
Keywords: ABS; Ferric chlorides; OMT; Nanocomposites; Catalyzing carbonization;

The nylon 6/MgAl layered double hydroxide (MgAl-LDH) nanocomposites have been prepared by melt intercalation of nylon 6 into the part organic dodecyl sulfate (DS) anion-modified MgAl(H-DS) interlayers. The structures and properties of MgAl(H-DS) and corresponding nanocomposites were characterized by ion chromotography, X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and cone calorimeter test (CCT). The nanoscale dispersion of MgAl(H-DS) layers in the nylon 6 matrix has been verified by the disappearance of d 001 XRD diffraction peak of MgAl(H-DS) and the observation of TEM image. DSC tests evince that these exfoliated MgAl(H-DS) layers play the role of nucleating agents with strong heterogeneous nucleation effect on the crystallization of nylon 6 and increase its crystallization temperature over 12 °C with only 5 wt% MgAl(H-DS). TGA tests show that the effect of alkaline catalysis degradation from LDH on nylon 6 decreases the thermal stability of nylon 6/MgAl-LDH nanocomposites. The data from the cone calorimeter tests show that the HRR and MLR values of the sample with 5 wt% MgAl(H-DS) decrease considerably to 664 kW/m2 and 0.161 g/m2  s from 1064 kW/m2 and 0.252 g/m2  s of pure nylon 6, respectively. This kind of exfoliated nanocomposite is promising for the application of flame-retardant polymeric materials.
Keywords: Layered double hydroxide; Nylon 6; Melt intercalation; Nanocomposite; Crystallization; Flame retardancy;

Hydroxylbenzylthioethers as novel organic thermal stabilizers for rigid PVC by Peng Liu; Lunyu Zhu; Yan Fang; Huaiping Zhang; Dehong Chen; Kai Xu; Mingcai Chen (503-508).
An investigation was carried out on the performances of hydroxylbenzylthioethers employed as organic thermal stabilizers for rigid poly(vinyl chloride). The efficiency of these compounds as thermal stabilizers was evaluated by using Haake polydrive mixer and TGA. The stabilizing efficiency was compared with Ca–Zn soap and methyltin stabilizer. Hydroxylbenzylthioethers exhibit greater efficiency than both of these stabilizers. This is attributed to the ability of these compounds to prevent the formation of polyene sequences. The hydroxylbenzylthioethers-stabilized PVC showed a slightly lower glass transition temperature (T g) in comparison with the original PVC. Hydroxylbenzylthioethers and epoxidized soybean oil (ESBO) exhibit synergistic effect on the stabilizing effect, when the mass ratios of ESBO to hydroxylbenzylthioethers are less than 0.5.
Keywords: Poly(vinyl chloride); Organic thermal stabilizer; Hydroxylbenzylthioethers; Degradation;

The sulfonated poly(ether sulfone) (SPES) was successfully prepared using chlorosulfonic acid as a sulfonating agent. Diglycidylether of bisphenol-A (DGEBA) epoxy resins were modified with different contents of SPES, and the thermal and mechanical interfacial properties of DGEBA/SPES blends were investigated. As a result, the surface free energy of the blends was increased by the addition of SPES. DSC measurements revealed that the curing reaction was delayed with the increase of SPES content. Whereas, the thermal stabilities of the blends were slightly decreased as the SPES content increased. Meanwhile, the glass transition temperature and fracture toughness of the blends were increased with increasing SPES content, due to the improved intermolecular interactions, such as hydrogen bonding, between the hydroxyl group of DGEBA and the sulfonic group of SPES in the blends. The agreement could be observed by SEM which revealed phase separated morphology of DGEBA/SPES blends.
Keywords: Epoxy resin; Poly(ether sulfone); Thermal stabilities; Mechanical properties;

The degradative activities of neutral protease against chitosan samples with different molecular parameters were characterized. The effects of the degree of deacetylation (DD) and molecular weight (MW) of chitosan on its susceptibility to degradation were investigated. The DD and MW of the chitosans were determined using potentiometric titration and viscometry, respectively. The molecular weight distribution of initial and degraded commercial chitosan was investigated by gel permeation chromatography. Initial degradation rates (r) were determined from the plots of viscosity decrease against time of degradation. The time courses of degradation of chitosans with neutral protease were non-linear and the enzymatic hydrolysis was an endo-action. Classical Michaelis–Menten kinetic parameters were measured by analyzing the amount of reducing sugars and Eadie–Hofstee plots established that hydrolysis of chitosan by neutral protease obeyed Michaelis–Menten kinetics. Michaelis–Menten parameters and initial degradation rates were calculated and compared to determine the influences of DD and MW on hydrolysis. The results showed that higher DD and higher MW chitosans possessed a lower affinity for the enzyme and a slower degradation rate. Those samples with a lower DD and lower MW were more susceptible substrates.
Keywords: Chitosan; Neutral protease; Degradation; Michaelis–Menten kinetics;