Enzymatic degradation of some nanocomposites of poly(vinyl alcohol) with starch

A study of the enzymatic degradation of some montmorillonite-containing nanocomposites of poly(vinyl alcohol) with starch was based on the determinations of mass loss and the reducing sugars. The degraded residues have been examined by FT-IR spectroscopy and optical microscopy. It has been established that the nanoparticles hinder degradation, while the susceptibility to enzymatic degradation varies in the order: PVA/starch/nanocore > PVA/starch/Bentonite > PVA/starch/Peruvian clay.     

Enzymatic degradation of poly(L-lactide) and poly(epsilon-caprolactone) electrospun fibers

Poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) ultrafine fibers were prepared by electrospinning. The influence of cationic and anionic surfactants on their enzymatic degradation behavior was investigated by measuring weight loss, molecular weight, crystallinity, and melting temperature of the fibers as a function of degradation time. Under the catalysis of proteinase K, the PLLA fibers containing the anionic surfactant sodium docecyl sulfate (SDS) exhibited a faster degradation rate than those containing cationic surfactant triethylbenzylammonium chloride (TEBAC), indicating that surface electric charge on the fibers is a critical factor for an enzymatic degradation. Similarly, TEBAC-containing PCL fibers exhibited a 47% weight loss within 8.5 h whereas SDS-containing PCL fibers showed little degradation in the presence of lipase PS. By analyzing the charge status of proteinase K and lipase PS under the experimental conditions, the importance of the surface charges of the fibers and their interactions with the charges on the enzymes were revealed. Consequently, a "two-step" degradation mechanism was proposed: (1) the enzyme approaches the fiber surface; (2) the enzyme initiates hydrolysis of the polymer. By means of differential scanning calorimetry and wide-angle X-ray diffraction, the crystallinity and orientation changes in the PLLA and PCL fibers during the enzymatic degradation were investigated, respectively.     

Influence of Teflon Substrate on Crystallization and Enzymatic Degradation of Polymorphic Poly（butylene adipate）

Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate)(PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA α crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA β crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with α crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.     

Enzymatic degradation of highly phenolic lignin-based polymers (lignophenols)

Enzymatic degradation of two lignin-based polymers (lignophenols), lignocatechol and lignocresol, prepared by selectively grafting catechol and p-cresol to C_α positions of lignin, respectively, were carried out in aqueous organic solvents. Both lignophenols showed high reactivity in the peroxidase-catalyzed oxidation. Structural analyses by NMR spectroscopies revealed that the degraded lignophenols contained aliphatic chain content, which might be mainly formed in the reduction of the intermediate initially generated by the aromatic ring cleavage. Lower amount of aromatic units in the lignophenols after degraded by peroxidase also indicted the cleavage of aromatic rings. Due to the substitution of phenols at C_α positions of lignin, the degraded lignophenols did not have carbonyl structure, which was abundant in the biodegradation products of native lignin. The two lignophenols were also degraded by Rhus vernicifera laccase. But the degree of degradation was lower than that of the degradation by peroxidase, which might be due to the low activity of laccase on the lignin moieties in lignophenols.     

Heat of fusion and lamellar structure of polyethylene single crystal mats

Recently published results for solution crystallized PE single crystals have shown, that the experimental heat of fusionH ^* is higher, if the solvent is exchanged to silicon oil (oil suspension samples) as compared with dried mats. This has been interpreted by the collapse of the original hollow pyramids during drying, inducing lateral defects within the lamellae. The present investigation does not confirm this unexpected result.H ^* of dried mats (T _c 66 to 91 °C) and of the corresponding oil suspension samples agree within the rather small limits of experimental error. The crystallinities as derived fromH ^*, density or WAXS are in excellent agreement.SEM micrographs of cold fractured dried mats show their spongy macromorphology, but TEM micrographs of stained ultra-thin sections reveal the lamellar morphology of the walls, consisting of curved lamellae and stacked hollow pyramides. If a dried mat is sintered at room temperature, a dense transparent film is obtained with a rather regular stacked morphology of large flat lamellae.H ^* of these films agrees with that of the original mat.Dedicated to Professor Dr. F. H. Müller.     

Crystal structure and morphology of poly(16-hexadecalactone) chain-folded lamellar crystals

Solution-grown, chain-folded lamellar crystals of poly(16-hexadecalactone) (PHDL) were crystallized isothermally from 1-hexanol at 70 degrees C. The morphology of lozenge-shaped crystals was studied by TEM and AFM. The lamellae are ca. 10 nm thick and the chains run orthogonal to the lamellar surface with folding along (110) and (110) planes. The crystal structure of PHDL was determined by XRD and election diffraction of single crystals. The chains are in the 2(1) helix conformation close to all-trans and the structure consists of an orthorhombic unit cell with a P2(1)2(1)2(1) space group with the lattice constants a = 0.746 +/- 0.001 nm, b = 0.504 +/- 0.001 nm, and c (chain axis) = 4.116 +/- 0.003 nm. There are two chains per unit cell, which exist in an antiparallel arrangement. Molecular packing structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to a axis, were +/-40 degrees for the corner and center chains, respectively. By using the electron and XRD data, the best molecular packing model was refined to R-factors of 0.168 and 0.196, respectively. A brief comparison of chain-packing structure is also made with related polymer structures.     

Enzymatic degradation of oxidized cellulose hydrogels

The cellulose-based hydrogel with abundant aldehyde groups was prepared by periodate oxidation of cellulose hydrogel prepared by dissolution-regeneration of cellulose by aqueous LiOH/urea solvent. Aldehyde groups could be introduced retaining the nanoporosity of the cellulose gel. The enzymatic degradation of three grades of oxidized cellulose hydrogel, with aldehyde contents of 3.3, 8.1 and 18.6 per 100 glucose unit, was carried out using solutions containing cellulase and β-glucosidase at 37 °C up to 48 h. The degradation of oxidized gels was remarkably slower than that of original cellulose gel, depending strongly on the degree of oxidation. The portion except for the amount of glucose released was greater than the degree of oxidation, but became closer to the latter with increase in the degree of oxidation. This behavior can be interpreted in terms of the enzymatic recognition of the chemically modified cellulose chains.     

Synthesis,physical properties and enzymatic degradation of bio-based poly(butylene adipate-co-butylene furandicarboxylate) copolyesters

A series of bio-based poly(butylene adipate-co-butylene furandicarboxylate) (PBAFs) copolyesters were synthesized from 2,5-furandicarboxylic acid (FDCA), adipic acid (AA), and 1,4-butanediol (BDO) through a two-step polycondensation reaction. The copolyesters were characterized by ¹H NMR, GPC, DSC, XRD and tensile tests, and their enzymatic degradation behaviors were also investigated. They were random copolymers whose composition was well controlled and the weight average molecular weight (M_w) ranged from 54,100 to 76,800 g/mol. By combining the results of DSC and XRD, with increasing FDCA content, PBAFs changed from semi-crystalline polymers to nearly amorphous polymers, then to semi-crystalline polymers again. Specifically, the crystallizability and melting temperature (T_m) decreased with FDCA content 0–50 mol%, but rose again at FDCA content 75–100 mol%. And, the glass transition temperature (T_g) increased continuously with increasing FDCA content. Consequently, the tensile modulus and strength decreased but the ultimate elongation increased at lower FDCA content (0–50 mol%), which were converse at higher FDCA content (75–100 mol%). Especially, the P(BA-40 mol% BF) shows outstanding elasticity and rebound resilience. In addition, the influences of FDCA content on the enzymatic degradation by lipase from porcine pancreas were studied in terms of the weight loss and morphological change. At FDCA content of 0–50 mol%, the copolyesters showed biodegradability but only the degradation rate of P(BA-10 mol% BF) was faster than PBA. When the FDCA content were 75–100 mol%, they were actually un-degradable. Thus, depending on their composition, PBAFs might find applications from biodegradable elastomers to thermoplastics.     

Effect of copolymerized butylene terephthalate chains on polymorphism and enzymatic degradation of poly(butylene adipate)

The introduction of aromatic butylene terephthalate (BT) units into the backbone chains of aliphatic poly(butylene adipate) (PBA) not only changes the mechanical performance of the resultant P(BA-co-BT) copolymers but also affects their biodegradability. Because of the polymorphism of PBA homopolymer, the copolymerized BT units may also influence the polymorphic crystal structure as well as the biodegradation behavior. In this work, three P(BA-co-BT) copolymers with BT contents as 10, 20, and 25 mol% were chosen to study their polymorphic crystal structure, thermal properties and enzymatic degradation by means of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and gravimetric methods. The results reveal that the P(BA-co-BT) copolymers with BT contents below 25 mol% can form polymorphic crystal structures after melt-crystallization at different temperatures. However, the recrystallization and transformation of polymorphic crystals are strongly affected by the rigid BT units. The enzymatic degradation rates of P(BA-co-BT) copolymers decrease with increasing the BT contents. The influences of the BT units on the polymorphism and enzymatic degradation are discussed in terms of the motion of PBA chains that copolymerized with BT units. It has been concluded from the examination of solid-state microstructure that the influence of the aromatic BT units on the motion of biodegradable PBA chains heavily influences the biodegradability.     

Enzymatic degradation of trichloroethylene using enzyme extracts isolated from a bacterial consortium

Degradation of trichloroethylene (TCE) using crude enzyme extracts from a bacterial consortium was examined for wastewater treatment. The effects of pH, chemical induction, and cofactor were investigate. Enzyme extracts showed an optimal activity (3.03±0.03 mg of TCE/[mg of protein·d]) at neutral pH (6.5–7.5). In an attempt to increase the production of effective enzymes for TCE degradation, chemical induction using both toluene and TCE in the growth of the bacterium consortium was conducted. Although the induction increased the overall production of protein by about fourfold, the activity of the extracts was only slightly improved (up to 3.40 mg of TCE/[mg of protein·d]), indicating that the induction did not specifically enhance the production of TCE-degrading enzymes. Interestingly, the addition of a cofactor (up to 0.02 mg/mL), NADH, led to an initial reaction rate of 5.30±0.05 mg of TCE/(mg of protein·d). This observation demonstrated that the availability of the cofactor played an important role in determining the overall degradation reaction rates. The observations with NADH were in agreement with the assumption that toluene monooxygenases (which are NADH dependent) are the key enzymes for the degradation reactions.     

Thermal degradation of poly(methyl-n-hexylsilylene)

Thermal degradation of poly(methyl-n-hexylsilane) in the solid state in absence of oxygen reveals formation of a cyclic pentamer between 150 and 250°C. Polymer is gradually degraded to an intermediate molecular weight distribution. The weight average of this new distribution is not only temperature-dependent, but is also a function of viscosity of the polymer and nature of chain ends. As no insolubles or Si? H groups are formed, the degradation mechanism is most likely a back-biting mechanism induced by active chain ends such as silyl anions or Si? Cl rather than a homolytic cleavage of the main chain. A concurrent intramolecular rearrangement reaction is also proposed. Moreover, this study proposes an explanation to the trimodal molecular weight distribution obtained by the Wurtz coupling of dichlorosilanes with molten sodium in refluxing toluene. © 1995 John Wiley & Sons, Inc.     

Studies of photooxidative degradation of poly(vinyl chloride)/poly(ethylene oxide) blends

The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004     

Crystal structure, thermal behavior and enzymatic degradation of poly(tetramethylene adipate) solution-grown chain-folded lamellar crystals

Solution-grown chain-folded lamellar single crystals of poly(tetramethylene adipate) (PTMA) were prepared from a dilute solution of 2-methyl-1-propanol by isothermal crystallization. PTMA crystals were hexagonal-shaped and polyethylene decoration of the crystals resulted in a "six cross-sector" surface morphology and showed that the average direction of chain folding is parallel to the crystal growth planes of [110] and [010]. Chain-folded lamellar crystals gave well-resolved electron diffraction diagrams corresponding to all the equatorial reflections of the X-ray fiber diagram obtained from stretched PTMA melt-quenched film (beta structure). The unit cell parameters of the beta structure of PTMA were determined as a = 0.503 nm, b = 0.732 nm and c (fiber axis) = 1.442 nm with an orthorhombic crystal system. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. The setting angle, with respect to the a axis, is +/-46 degrees for the corner and center chains. Thermal behavior of lamellar crystals has been investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The lamellar thickness at the edges of the crystal increased after thermal treatment with taking the molecular chains into recrystallization parts; the holes then opened up at the thickening front of the crystal. The morphological changes of lamellar crystals after enzymatic degradation by Lipase type XIII from Pseudomonas sp. and water-soluble products were characterized by TEM, AFM, gel permeation chromatography, high performance liquid chromatography and fast atom bombardment mass spectrometry. The degradation progressed mainly from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The central portion of single crystals was often degraded by enzymatic attacks. This result combined with thermal behavior indicates that the loosely chain-packing region exists inside the single crystal, and that molecular chains in this region have higher mobility against thermal and enzymatic treatments.     

Thermal degradation kinetics of poly(methylvinylsilylene-co-styrene)

Thermal degradation kinetics of poly(methylvinylsilylene-co-styrene) copolymers, viz., PMVSS-I to PMVSS-V obtained by reacting methylvinyldichlorosilane (MVDCS) and styrene in 1:0.25, 1:0.5, 1:1, 1:3 and 1:7 mole ratios under dechlorination conditions, using sodium, was studied by thermogravimetry. The homopolymer, poly(methylvinylsilane) (PMVS), synthesized from MVDCS using sodium was also subjected to the above study for comparative evaluation. The kinetic parameters for thermal degradation, viz., activation energy (E) and pre-exponential factor (A) for the above polymers were estimated by non-isothermal kinetic methods such as Mac Callum-Tanner (M-T), Horowitz-Metzger (H-M), Madhusudhanan-Krishnan-Ninan (MKN) and Coats-Redfern (C-R). The order for thermal degradation of PMVS was found to be almost 0. In the case of the copolymers, the order was 1 for PMVSS-I and 2 for PMVSS-II to PMVSS-V. The observed difference in the order for thermal degradation of PMVSS-I when compared to the other copolymers is attributed to the presence of polysilyl linkages in PMVSS-I. It was found that the activation energy and pre-exponential factor showed an increase in trend with increase in concentration of styrene in the copolymer system.     

Thermotropic polyesters. 1: Synthesis, characterization and thermal transition of poly[4,4-bis(ω-alkoxy)biphenyl isophthalate]

A new homologous series of thermotropic polyesters has been synthesized by polycondensation reaction between isophthaloyl chloride and mesogenic diols 4,4^′-bis(ω-hydroxyalkoxy)biphenyl in which the spacer length is varied from 3 to 6 methylene units. The thermal behavior of the polymers has been characterized using polarized light microscopy and differential scanning calorimetry (DSC). The odd members exhibit a smectic C (S_C) phase in a narrow temperature interval, while the even members form a smectic A (S_A) phase in a broader temperature range. All of the obtained compounds were characterized by conventional spectroscopic methods.     

Thermal degradation of poly(vinyl chloride)

This paper presents an initial attempt at describing poly(vinyl chloride) (PVC) thermal degradation through a semi-detailed and lumped kinetic model. A mechanism of 40 species and pseudocomponents (molecules and radicals) involved in about 250 reactions permits quite a good reproduction of the main characteristics of PVC degradation and volatilization. The presence of the two step mechanism—the first step of which corresponds to dehydrochlorination and the second to the tar release and residue char formation—are correctly predicted both in quantitative terms and in the temperature ranges. The model was validated by comparison with several thermo gravimetric analyses, both dynamic at different heating rates, and isothermal. When compared with the typical one step global apparent degradation models, the approach proposed here spans quite large operative ranges, especially when it comes to predicting product distributions. The initial results of these product predictions, even though quite preliminary, are encouraging and confirm the validity of the model.     

The morphological effects upon enzymatic degradation of poly(butylene succinate-co-butylene terephthalate)s (PBST)

In this work, the enzymatic degradation of poly(butylene succinate-co-butylene terephthalate) (PBST) copolyesters was studied using the lipase from Pseudomonas (Lipase PS^®). The biodegradation behavior was found to strongly depend on the overall impacts of several important factors as the BT comonomer structure and molar content, thermal characteristics, morphology, the enzyme-substrate, and so forth. Further, the biodegraded residual film samples were allowed to be analyzed by means of gel permeation chromatography (GPC), proton nuclear magnetic resonance (¹H NMR), differential scanning calorimeter (DSC), small angle X-ray scattering (SAXS), and scanning electron microscope (SEM). On the experimental evidences, an exo-type mechanism of enzymatic chain hydrolysis preferentially occurring in the amorphous region was suggested for the PBST film samples.     

Thermal degradation of poly(vinylpyridine)s

The thermal stability and the temperature at which maximum degradation yields are detected were quite similar for both poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP). However, considerable differences among the thermal degradation products of both polymers were detected indicating a correlation between the polymer structure and the degradation mechanism. Direct pyrolysis mass spectrometry analyses revealed that P2VP degrades via a complex degradation mechanism, yielding mainly pyridine, monomer, and protonated oligomers, whereas depolymerization of P4VP takes place in accordance with the general thermal behaviour of vinyl polymers. The complex thermal degradation behaviour for P2VP is associated with the position of the nitrogen atom in the pyridine ring, with σ-effect.     

Crystallization kinetics of poly(hexamethylene succinate)

Isothermal and nonisothermal crystallization kinetics of polyester 64 have been investigated by means of differential scanning calorimetry and optical microscopy. The Avrami analysis has been performed to obtain the kinetic parameters of primary crystallization. These indicate a three-dimensional spherulitic growth on heterogeneous nuclei for the isothermal crystallization, whereas an sporadic nucleation becomes dominant in the nonisothermal crystallization. The maximum crystallization rate of polyester 64 was deduced to take place at a temperature close to −3 °C. Polarizing light microscopy showed that spherulites with a negative birefringence are formed during isothermal crystallization, whereas transmission electron microscopy indicates that the b crystallographic axis is aligned parallel to the spherulitic radius.     

Chemical degradation of poly(2-aminoethyl methacrylate)

Poly(2-aminoethyl methacrylate) (PAMA) has a pK_a of approximately 7.6 and is chemically stable in acidic or neutral aqueous solution in its protonated form. However, chemical degradation of PAMA is known to occur in alkaline media as its primary amine groups become deprotonated (He L et al. Macromolecules 2007; 40: 4429-38). In the present work, the effect of temperature, pH and polymer concentration on the rate of PAMA degradation in dilute aqueous solution has been examined. ¹H NMR spectroscopy indicates that both elimination of 2-aminoethanol and formation of 2-hydroxyethyl methacrylamide repeat units occur above pH 9; elimination is observed first and occurs to a greater extent. FT-IR studies of aqueous PAMA solutions aged at pH 12 and 50 °C confirm the presence of anionic carboxylate groups, which suggests that such elimination is simply due to ester hydrolysis. A control experiment suggests that methacrylamide formation occurs via internal rearrangement, rather than by amidation of the remaining ester groups by the eliminated 2-aminoethanol.