Changes In Molecular Weight Distribution Research Articles

Degradation of post-consumer polypropylene materials exposed to simulated recycling—mechanical properties

Two post-consumer polypropylene (PP) materials have been examined and compared using a simulated recycling test procedure consisting of repeated cycles of alternating extrusion and accelerated thermo-oxidative ageing. The materials were also subjected to repeated extrusion and thermo-oxidative ageing separately. The materials were characterized by mechanical and chemical properties, such as elongation-at-break, oxidative induction temperature, carbonyl index and changes in molecular weight distributions. The different batches of recycled PP differed substantially in terms of durability and recycling potential. This illustrates one of the problems involved in handling recycled materials i.e. different batches and material streams may differ quite a lot. Interestingly, the elongation-at-break was significantly different for samples taken after ageing and extrusion, respectively. The elongation decreased upon each ageing step, and increased as a result of the subsequent extrusion. Furthermore, the combination of extrusion and ageing tended to degrade the materials faster compared to ageing or repeated extrusion performed separately.

ＭＡＬＤＩ‐ＭＳによる非イオン系界面活性剤の生分解機構の解析

Bacterial biodegradation mechanisms of non-ionic surfactants under aerobic conditions were studied by means of matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). First, biodegradation intermediates of octylphenol polyethoxylate (OPEO) were characterized by MALDI-MS. Since the formation of carboxylated OPEO (OPEC) and the changes in molecular weight distribution during biodegradation test were observed, it was proposed that the biodegradation of OPEO was proceeded mainly according to the exo-scission of EO chain accompanied with oxidation of the hydroxyl terminal side. Then, to clarify the mechanisms of the oxidative biodegradation in detail, biodegradation test was carried out using 18O-labeled water as a incubation medium. The incorporation behavior of 18O into OPEC molecules suggested that the formation of an enzyme (or coenzyme)-substrate complex linked via a covalent bond might be formed as a reaction intermediate. Finally, biodegradation profiles of non-ionic surfactants with a variety of hydrophobic moieties were investigated using 18O-labeled water. The incorporation rates of 18O into corresponding carboxylated intermediates were correlated with the hydrophobicity of the surfactants.

Molecular weight distribution changes during degradation and release of PLGA nanoparticles containing epirubicin HCl

The molecular dynamics of the degradation process of poly(lactic-co-glycolic acid) nanospheres were investigated during the degradation process usually observed when these polymers are used as controlled release carriers. The molecular weight distribution of PLGA samples was determined over a period of 32 days by accurately analyzing the molecular weight distribution of the polymer as a function of time as degradation progressed. The molecular weight distribution shifted gradually to lower average molecular weights over 32 days, with significantly smaller molecular weight components appearing at 8–12 days. In addition, the degradation of nanospheres containing epirubicin HCl was analyzed and increasing the amount of epirubicin from 1.7 to 3.4 to 6.7 wt% was found to hasten the degradation of the nanoparticles and subsequently affect the release behavior from these particles. This is believed to be the first time that such molecular dynamics have been presented for the degradation of PLGA nanoparticle formulations containing a drug for controlled delivery.

Enzymatic degradation behavior and mechanism of Poly(lactide-co-glycolide) foams by trypsin

The purpose of this study is to investigate the enzymatic degradation behaviors of porous poly(lactide-co-glycolide) (PLGA) foams in the presence of trypsin, in comparison with their hydrolytic degradation. To inspect the effect of trypsin on the degradation of PLGA, both the hydrolytic and enzymatic degradation of non-porous PLGA samples were also performed. The changes of molecular weight and molecular weight distribution (polydispersity) during the degradation were determined by gel permeation chromatograph. And the changes of weight, thickness and morphology with the degradation were also measured. The degradation of PLGA displayed as two stages. In the first stage, the molecular weight of PLGA decreased continuously with degradation time, whereas little weight loss occurred. But in the second stage, the molecular weight of PLGA had decreased to a low value and was almost unchanged with time, while the sample experienced significant weight loss. And it was found that the presence of trypsin could significantly accelerate the weight loss rates of all the PLGA samples, but it caused little difference in the decrease of molecular weight and the change of PLGA composition between the enzymatic and hydrolytic degradation. Therefore, the enzymatic degradation of PLGA was still primarily a hydrolysis process. A mechanism of enzymatic degradation was proposed that the trypsin could enhance the weight loss of PLGA by acting as surfactant to push the dispersion of degradation products into water even though they could not dissolve in water.

Structural characteristics of pectic polysaccharides from olive fruit ( Olea europaea cv moraiolo) in relation to processing for oil extraction

In the olive oil industry technical enzyme preparations are used as processing aids to improve the extraction yield and product quality. In order to obtain more insight in the mechanisms by which these enzyme preparations lead to a higher yield and a better quality, the effect of these preparations on the structure of the pectic polysaccharides present in the cell wall of olive fruit was investigated. Four pectin-rich fractions were isolated from the cell wall material of non-enzyme treated and enzyme treated olive fruit by successive extractions with cold buffer, hot buffer, chelating agents and diluted alkali and analysed. The results revealed that the use of technical enzyme preparations during processing mainly affected the pectic material present in the cold and hot buffer fractions. The structures of the arabinose-rich pectic polysaccharides solubilised by extraction with chelating agents and diluted alkali were barely affected by the use of enzyme preparations. The changes of the buffer soluble pectic material were reflected by a decrease in methyl esterification, a change in molecular weight distribution and a degradation of the (1→4)-linked galactan chains. No differences were observed in the composition of the arabinan chains. Also, the structural features of the polysaccharides present in the vegetation waters, the liquid by-product of olive processing, were studied. The sugar composition indicated the presence of mainly material of pectic origin in the vegetation waters. As a result of enzymatic processing the degree of methyl esterification decreased, the profile of the molecular weight distribution changed and the (1→4)-linked galactan chains were degraded as was also shown for the buffer soluble pectic polysaccharides.

Process-induced changes in whey proteins during the manufacture of whey protein concentrates

Abstract Samples of cheese whey or acid casein whey obtained from commercial plants during the different stages of whey protein concentrate (WPC) manufacture were analyzed for protein composition and the extent of protein aggregation. Protein composition was determined by size exclusion chromatography (SEC) and electrophoresis, while the degree of protein aggregation was determined through the changes in molecular weight distributions monitored by SEC combined with multi-angle laser light scattering. The results show that there were some differences between the compositions of protein between the two types of wheys with the acid casein whey also containing lower proportions of “soluble” aggregates than the cheese whey. Ultrafiltration/diafiltration processes caused a removal of the non-protein, low molecular weight components, but had no significant effect on protein composition and aggregation. Evaporation and subsequent spray drying of the ultrafiltered retentates caused no significant changes in any of the whey protein components. Differences in functionality of WPC products are probably more related to modifications of proteins and other components caused by the processes that are used in cheese or casein manufacture rather than to the WPC manufacturing process.

Degradation kinetics of polyethylene terephthalate in supercritical methanol

AbstractDegradation of polyethylene terephthalate (PET) in supercritical methanol was investigated to develop a chemical recycling process for waste plastics. Continuous kinetics analysis was applied to the experimental data. A batch reactor was used at 573 K under the estimated pressure of 20 MPa for a reaction time of 2–120 min. PET decomposed to its monomers, dimethyl terephthalate (DMT), and ethylene glycol (EG), by methanolysis in supercritical methanol. PET with a weight‐average molecular weight of about 47,000 was converted to oligomer with that of 3,000 in 300 s and with that of 1,000 in 600 s. The largest yield of DMT was 80 mol % at 7,200 s and that of EG was 60 mol % at 3,600 s. Reaction products were analyzed with size exclusion chromatography, gas chromatography‐mass spectrometry, and reversed phase liquid chromatography. The molecular‐weight distribution (MWD) of the products was obtained as a function of reaction time. The yields of monomer components of the decomposition products, including byproducts, were measured. Continuous kinetics theory was developed to analyze the decomposition behavior. The theory includes MWD change of polymer by random and specific scissions and secondary reactions for monomer components. Change of MWD and monomers as a function of time was simulated by the continuous kinetics.

Changes in molecular weight forms of inhibin A and pro-alpha C in maternal serum during human pregnancy.

Maternal serum pools obtained from healthy women throughout normal pregnancy were fractionated by a combined immunoaffinity chromatography, preparative PAGE, and electroelution procedure. Inhibin A and the pro-alpha C region of the inhibin alpha-subunit were determined in the eluted fractions by specific ELISAs, and the profiles of immunoactivity characterized in terms of molecular weight and percent recovery. The molecular weight patterns of inhibin A and pro-alpha C in serum during early pregnancy (<19 wk gestation) showed peaks between 25-40K and approximately 60K, consistent with the presence of known mature and larger precursor inhibin forms. However, during late pregnancy (>19 wk gestation), an increase in the proportion of smaller molecular weight forms (from 2% to approximately 25%) of inhibin A and pro-alpha C of unknown structure were observed in the less than 30K and less than 25K regions, respectively. To assess whether this change in molecular weight distribution in late pregnancy was related to the method of serum collection, serum and plasma from women during early and late pregnancy were collected and snap-frozen. Three pools [one from early pregnancy (12-15 wk), two from late pregnancy (28-39 wk)] of serum and plasma were then fractionated as described above. No differences in molecular weight patterns of inhibin A and pro-alpha C were observed between serum and plasma pools obtained in early pregnancy. However, in late pregnancy there was a reduction in the proportion of low molecular weight forms between serum (25% inhibin A, 35% pro-alpha C) and plasma (12% and 17%, respectively), but not to the low levels seen in early pregnancy. Incubation of iodinated 30K human inhibin A with serum or plasma obtained from early or late pregnancy showed no evidence of cleavage, suggesting that 30K inhibin A is not the cleavage precursor. It is speculated that the formation of small molecular weight forms of both inhibin A and pro-alpha C is attributed to proteolytic changes, in part induced in the circulation during late gestation and in part by the placenta before secretion. It is concluded that inhibin A and pro-alpha C are processed in late pregnancy by more than one mechanism to form low molecular weight circulating forms of unknown structure.

Radical polymerization of methyl methacrylate and styrene in the presence of ferrocene

The influence of ferrocene on the kinetic parameters of methyl methacrylate (MMA) or styrene polymerization is investigated. It is shown, that in the presence of ferrocene the growth of the initial rate of polymerization is accompanied with significant decrease of the polymerization degree of polymer obtained when peroxides are used as the polymerization initiators. The polymerization kinetics parameters are evaluated. Its demonstrated that the process of polymerization in the presence of a ferrocene has a low activation energy, that allows to carry out the polymerization at lower room temperatures. The influence of the ferrocene on the molecular-mass characteristics of poly(methyl methacrylate) (PMMA) was studied and it was found that the influence of ferrocene on PMMA molecular mass is determined by the nature of the initiator used. The decomposition temperature of PMMA increases with the increase of ferrocene concentration. Monte-Carlo technique was used for numerical simulation of MMA radical polymerization kinetics in the presence and in the absence of ferrocene and to follow the change of molecular-weight distribution during the polymerization. The peculiarities of polymer radical concentration changes at the initial stage of polymerization are shown. Satisfactory correspondence between calculated and experimental data was obtained.

Uptake and distribution of rare earth elements in rice seeds cultured in fertilizer solution of rare earth elements

The uptake behavior of rare earth elements (REEs) under pot conditions using deionized water and a REE fertilizer solution as the culture media as well as the distribution of REEs in rice proteins were studied. The uptake of REEs in rice seeds increased dramatically after a lag period of approximately three days. Roots can accumulate a much higher content of REEs than germs and the resting seeds. The REE content in each water-soluble (albumin) and salt-soluble (globulin) component of the rice seeds accounted for 5–8% and 4–6% of the total REEs, respectively. However, there are less than 1.5% of the total REEs were found in the alcohol-soluble (prolamin) and acetic acid-soluble (glutelin) components. The high performance liquid chromatography (HPLC) in the gel permeation and the reserved-phase were used to monitor changes in the molecular weight distribution changes of the soluble proteins of rice seeds during germination after having been cultured in the same solution for seven days. No changes occurred in the prolamin, while a slight change occurred in the albumin, globulin and glutelin. Fractionation of the albumin of rice seeds cultured in a REE fertilizer solution on the Sephadex G-100 column indicated that REEs, especially Ce, La, Pr and Nd, were associated mainly with biological compounds of a molecular weight between 10,000 and 12,000.

Mechanism and molecular weight model for thermal oxidation of linear ethylene–butene copolymer

The mechanism of thermooxidative degradation at 80°C of a narrow distribution linear ethylene–butene copolymer has been described by determining the chemical modifications and molecular weight distribution changes occurring in the polymer chains, and successively fitting the experimental results with a mathematical model which allows scission and crosslinking reactions to occur simultaneously. Degradation takes place with autoacceleration and from the computer simulation a cubic dependence of the degree of crosslinking and degree of scission with exposure time was obtained. It was established that in this system scissions predominate over crosslinking, in accordance with the drop in average molecular weights and the concomitant accumulation of oxidation products.

Application of the plastein reaction to mycoprotein: II. Plastein properties

Abstract Mycoprotein peptide hydrolysates have been used as starting materials for plastein synthesis. Compared to other proteins studied, mycoprotein hydrolysates were a relatively poor substrate for the plastein reaction and generally led only to thixotropic viscous solutions, rather than to gelled products, and only low yields of insoluble plastein material. Once formed, however, the insoluble fraction remained insoluble over the whole pH range of 2–11. In contrast to many other plasteins, the mycoprotein material was not solubilised by detergents such as sodium dodecyl sulphate although, like others, it was largely solubilised by 50% (v/v) organic acids or 1 M NaOH and partially solubilised by chaotropic agents such as 8 M urea, 6 M guanidinium chloride and 7 M potassium thiocyanate. A combination of 8 M urea and 50% (w/v) citric acid completely solubilised the plastein to a clear solution. Gel filtration failed to reveal any change in peptide molecular weight distribution on plastein formation while ion-exchange chromotography showed some quantitative differences but these were difficult to interpret as most of the material did not adhere to the anion-exchange column under the conditions used. Amino acid analysis revealed a marked preferential incorporation of hydrophobic peptides into the plastein fraction. Differential scanning calorimetry results showed only broad peaks which suggested heterogeneous reaction mixtures and products with no well-defined structural elements. These results are entirely consistent with plastein formation proceeding via a purely physical aggregation pathway.

Ultrasonic depolymerization of hyaluronic acid

Hyaluronic acid (HA) was depolymerized by ultrasonication. Changes in molecular weight and molecular weight distribution were observed by size exclusion chromatography with a low-angle laser light scattering photometer. We investigated the influence of sonication intensity, temperature, HA concentration, coexisting cations and ionic strength. Results demonstrated that, with an increase of intensity, initial depolymerization rate ( k) increased and ultimatedepolymerized molecular weight ( M lim) converged to smaller size. The factors that change high-order structure of HA molecules had great influence upon the k, but not so much upon the M lim. For example, continuous sonication with 55 W depolymerized the HA to almost the same M lim (approximately 0.1×10 6), with a few exceptions. Where exceptions occurred, they were in concentrated monovalent cation solutions; the M lim increased up to about 0.3×10 6. Consequently, by regulating the sonication conditions, HA with the desired lower molecular weight and a narrow distribution could be prepared from high molecular weight samples.

Structural modification of poly(methyl methacrylate) by proton irradiation

A general survey is presented on the structural modification of poly(methyl methacrylate) (PMMA) by proton implantation. The implanted PMMA films were characterized by FT-IR attenuated total reflection (FT-IR ATR), Raman, Rutherford backscattering spectroscopy (RBS), gel permeation chromatography (GPC) and surface profiling. The ion fluence of 350 keV protons ranged from 2×10 14 to 1×10 15 ions/cm 2. The IR and Raman spectra showed the reduction of peaks from the pendant group of PMMA. The change of absorption and composition was observed by UV–VIS and RBS, respectively. These results showed that the pendant group is readily decomposed and eliminated by proton irradiation. The change of molecular weight distribution was also measured by GPC and G-value of scission was estimated to be 0.67.

Study of Degradation on Deuteration of a Diblock Copolymer of Polystyrene and Poly(ethylene-alt-propylene)

This paper reports a method of selectively deuterating the aromatic ring in a diblock copolymer of polystyrene and poly(ethylene-alt-propylene). The molecular weight distribution and molecular weight of the copolymer were determined by size exclusion chromatography and the extent of deuteration by 1H nuclear magnetic resonance spectroscopy. High levels of deuteration were sought with minimal changes in molecular weight distribution. A range of deuteration experiments were performed, some of which produced significant changes in molecular weight of the diblock copolymer. Changes in molecular weight are discussed with reference to groups in the copolymer chain.

Poly( l-lactide): VI Effects of crystallinity on enzymatic hydrolysis of poly( l-lactide) without free amorphous region

Poly( l-lactide) films without free amorphous region were prepared to have different crystallinities ( x cs) and therefore different crystalline thicknesses ( L cs) by allowing their crystallization to come to completion at different annealing temperatures ( T a s) from the melt. Their enzymatic hydrolysis catalyzed by proteinase K was investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The change in molecular weight distribution and surface morphology of the PLLA films during hydrolysis revealed that enzymatic hydrolysis of the PLLA films proceeded mainly via the surface erosion mechanism. Etching the inside of PLLA spherulites resulted from preferred enzymatic hydrolysis of the PLLA chains in the restricted amorphous region between the crystalline regions. Enzymatic hydrolysis rate ( R EH) of the PLLA films decreased monotonously with increasing the initial x c and L c according to the equation, R EH[μ g/(mm 2·h)]=0.36[1−0.01· x c (%)]. The PLLA chains in the restricted amorphous region between the crystalline regions was found to be rather hydrolysis-resistant compared with those in the free amorphous region as in a completely amorphous film. The lowest molecular weight specific peak in GPC spectra was ascribed to the PLLA chains of one fold in the crystalline region. The appearance and remaining of the low molecular weight specific GPC peaks ascribed to the chains of two- and three-fold in the crystalline region during enzymatic hydrolysis strongly suggest that the enzymatic hydrolysis of the PLLA films took place predominantly at the free and tie chains in the restricted amorphous region rather than at those in the folding surface of the PLLA lamellae. The relationship between the melting temperature ( T m) and L c was found to be T m K =472 [1−1.46/ L c (nm)] for PLLA films enzymatically hydrolyzed for 40 h.

Changes in cellulose supramolecular structure and molecular weight distribution during steam explosion of aspen wood

We have studied the cellulose supramolecular structure in pulps obtained by steam explosion of aspen wood. The pulps were bleached with hydrogen peroxide in an OQP-sequence and characterised by siz ...

Molecular recognition in radical template polymerization

In our previous study, when mixing polymer solutions in a common solvent, we have found the existence of a molecular recognition effect with regard to the chain length in the polycomplex formation. In the present work, we found a similar phenomenon to occur in template polymerization with regard to the template polymer. The system studied was template polymerization of methacrylic acid (MAA) on poly(N-vinylpyrrolidone) (PVP) or on poly(2-dimethylaminoethyl methacrylate) (PDMAEM). The polymerization, carried out in ethanol or in tetrahydrofuran was initiated with AIBN. A series of copolymerizations of methacrylic acid and methyl methacrylate on PDMAEM was performed under similar conditions. Changes in molecular weight distribution of PVP and PDMAE templates in the course of polymerization and copolymerization were studied by gel permeation chromatography. A method was elaborated which permitted simultaneous determination of MWD of the uncomplexed fraction of the template, the extent of polymerization of monomers, and the composition of the polycomplex formed. The recognition effect with regard to the chain length of the template was also observed in homopolymerization of MAA as well as in copolymerization of MAA with methyl methacrylate (MMA). The results obtained are discussed with regard to the composition of the complexes formed and to the template – daughter polymer interaction. There was no effect of the solvent used.

Photo-oxidative stability of paraloid acrylic protective polymers

The photo-oxidative stability of a series of commercial acrylic/methacrylic protective resins, which find use in consolidation and protection of art works, monuments and historical buildings, and are known by the name of Paraloids, has been investigated. The structural and molecular changes occurring under conditions of artificial solar light irradiation have been followed by FTIR and UV–Vis spectroscopy, and size exclusion chromatography. In all the resins the first degradative event which is detected is the molecular weight distribution change due to chain scissions and/or coupling of macroradicals. The overall stability of the polymers is strongly influenced by the presence of long alkyl side groups, such as butyl or isobutyl, whose oxidation is favoured by the presence of relatively labile hydrogen atoms. At the same time these polymers containing long ester groups undergo fast and extensive cross-linking together with some fragmentation and consequent weight losses. The resins containing only ethyl and methyl esters showed a good stability towards oxidation, reaching an equilibrium between scission reactions and macromolecular coupling which permit them to maintain their molecular characteristics during the ageing.

A size exclusion chromatography study of cellulose degradation

The degradation of cellulose is an important factor in the life of electrical insulation in power transformers and in the longevity of paper archives. Traditionally, degradation has been studied by following the decrease in the viscometric degree of polymerisation (DP) in a solvent such as copper ethylenediamine (CUEN). In this paper, we report a study of molecular weight distribution (MWD) changes in cotton linters, measured by size exclusion chromatography in dimethylacetamide/lithium chloride (DMAc/LiCl) solvent, during accelerated ageing in the laboratory. The initial mono-modal distribution changes to a multi-modal distribution during ageing, but eventually returns to mono-modal as the DP of the cotton reaches a limiting value of 150–200. Such complex changes in the MWD cannot be reflected truly in any average value such as the DP, nevertheless we show that the number average molecular weight (Mn) changes with time in very much the same way as viscometric DP and the changes can be fitted to the same kinetic model. The general trend is that the polydispersity of the material increases with ageing, as the distribution broadens, but the scatter in the data prevents any accurate trend analysis. The intermediate peak positions indicate preferential scission of molecules near the centre.