Number Of Scissions Research Articles

Additive Free Crosslinking of Poly-3-hydroxybutyrate via Electron Beam Irradiation at Elevated Temperatures.

When applying electron or gamma irradiation to poly-3-hydroxybutyrate (P3HB), main chain scissions are the dominant material reactions. Though propositions have been made that crosslinking in the amorphous phase of P3HB occurs under irradiation, a conclusive method to achieve controlled additive free irradiation crosslinking has not been shown and no mechanism has been derived to the best of our knowledge. By applying irradiation in a molten state at 195 °C and doses above 200 kGy, we were able to initiate crosslink reactions and achieved gel formation of up to 16%. The gel dose Dgel was determined to be 200 kGy and a range of the G values, the number of scissions and crosslinks for 100 eV energy deposition, is given. Rheology measurements, as well as size exclusion chromatography (SEC), showed indications for branching at doses from 100 to 250 kGy. Thermal analysis showed the development of a bimodal peak with a decrease in the peak melt temperature and an increase in peak width. In combination with an increase in the thermal degradation temperature for a dose of 200 kGy compared to 100 kGy, thermal analysis also showed phenomena attributed to branching and crosslinking.

Thermal oxidation of acrylonitrile-butadiene-styrene: Origin of the ductile/brittle transition

The accelerated thermal ageing of ABS films has been investigated over a wide range of exposure temperatures in air, by FTIR, GPC, AFM and tensile testing in order to determine the origin of the ductile/brittle transition during exposure. Besides formation of oxidation products and decrease of unsaturated bonds in butadiene phase, molar mass changes during oxidation have highlighted a chain scission process. If chain scission is associated to SAN phase, crosslinking occurs in butadiene phase, which is confirmed by measuring by AFM the relative modulus increase of the nanometric butadiene domains. At last, strain at break changes during exposures has been investigated taking into account the modifications of each phase on ABS embrittlement. It appears that ultimate elongation as a function of chain scission number follows a power law regardless of the other parameters showing that chain scission occurring in the SAN phase is the main process responsible for ABS embrittlement.

Correlation between crystallization and mechanical stress revealed by chain scission of segmented amide copolymer

By tuning hydrolysis duration of a segmented ether-amide copolymer (PEBA), a range of specimens presenting various macromolecular structures has been produced. Knowing that scissions occur predominantly at the bond between hard and soft blocks, for a given hard phase structure we study the impact of phase interconnection changes on strain-induced crystallization (SIC) occurring during tensile loading. The consequences of chain scissions on the structural reorganization involving SIC measured with in situ X-ray diffraction is considered here for the first time. A close correlation between stress and crystallinity induced under strain is highlighted whatever the chain scission number, i.e. the number of phase interconnections. As a result, the stress decrease observed at a given elongation can be interpreted as a consequence of a SIC weakening with the chain scission process. • A range of PEBA presenting various macromolecular structures has been produced after hydrolysis. • Chain scission changes strain-induced crystallization (SIC) occurring during tensile loading. • A close correlation between stress and crystallinity induced under strain is highlighted.

Improvement of Reaction Selectivity Performance with Alkali Charge and Reaction Time on Oxygen Delignification Process

The chemicals of NaOH is highly related to the quality of the pulp in the medium consistency oxygen process. This research used Acacia mangium and Eucalyptus pulp with KaNo 18. The condition of the medium consistency oxygen process, the temperature of 80 o C, oxygen pressure of 1 bar. Reaction time was 20 to 100 minutes at intervals of 20 minutes. NaOH charges 5 to 25 kg /t at intervals of 5 kg/t. The analysis parameters used are KaNo and viscosity. The higher value of NaOH charge and reaction time, the higher value of the delignification degree. The higher value of NaOH charge and the reaction time, the higher the value of chain scission number. The variation of NaOH charge in the same reaction time indicated that the higher NaOH charge value, the lower value of the polymerization degree. The variation in reaction time indicated the longer the reaction time, the lower the polymerization degree. The reaction selectivity value was not affected by the high value of NaOH charge. The longer the reaction time used, the lower the reaction selectivity.

Correlation Between Fock Reactivity and Intrinsic Viscosity of Dissolving Pulp During Cellulase Treatment

Cellulase treatment is an effective approach to upgrade dissolving pulp in a natural friendly way. In this study, a comprehensive experiment was conducted to understand the correlation of Fock reactivity increase and intrinsic viscosity decrease during cellulase treatment by varying cellulase charge and treatment time. Results showed that the Fock reactivity and intrinsic viscosity were improved simultaneously, which was caused by the cellulose chain scission. Two phases consisting of an initial fast phase and a second slow phase were identified for the improvement process, which was attributed to the varied recalcitrance of crystalline and amorphous regions of cellulose. A modeling between Fock reactivity and intrinsic viscosity was developed based on Ln S (natural logarithm of cellulose chain scission number). It can be used for prediction and controlling of cellulase treatment of dissolving pulp.

The crosslinking behaviour of cellulose in gamma irradiated paper

The behaviour of cellulose-based materials in a relatively low gamma dose range (less than 10 kGy) is of interest for the application of ionizing radiation for the preservation of cultural heritage. Different relationships between the absorbed dose and number of scissions or degree of polymerization (DP) were established on a large dose range (over 100 kGy). The significant decrease of DP was confirmed for doses range of interest for cultural heritage preservation, for pure cellulose paper and other sorts of commercial paper. However, other physical properties of the paper have less or no change for irradiation at doses below 10 kGy.The purpose of this study is to evaluate the changes induced by gamma irradiation to the hydrogen bonds structure in cellulose, in a low dose interval, by thermal analysis and infrared spectroscopy.Our results confirm the crosslinking behaviour for Whatman paper at low irradiation doses. A similar behaviour was observed for copy paper but with reduced intensity and higher statistical errors. This behaviour can explain why mechanical resistance of irradiated paper remains unchanged below a certain dose, as previously reported in a number of studies. The carbonyl content shows a continuous increase over the tested dose range but the increase of carbonyl content in Whatman paper at doses lower than 10 kGy is lower than the initial carbonyl content of copy paper. The ionizing radiation treatment for cultural heritage is not nonintrusive in case of paper but the degradation risks are minimal for doses below 10 kGy.

Additives to decrease cellulose chain scission during ozone bleaching of wheat straw pulp

Abstract The efficacy of different chemical additives like acetic acid, ammonium molybdate, diethylene triamine pentaacetic acid (DTPA), mannitol, methanol, per acetic acid (PAA), sodium hypochlorite (NaOCl) and sulfamic acid as carbohydrate protector during ozone bleaching of wheat straw pulp was studied. DTPA was found the most effective additive for ozone bleaching followed by the methanol. Using DTPA during ozone treatment improved the delignification efficiency by 13.8 %, bleaching efficiency by 19.8 %, selectivity of ozone by 124 % and reduced the chain scission number of glycosidic linkages in cellulose by 55.3 % compared to that of control. Ozone treatment along with DTPA reduced the Fe, Cu and Mn content in the pulp by 52 %, 27 % and 70 %, respectively. Use of methanol improved the delignification efficiency by 9.0 %, bleaching efficiency by 12.2 %, selectivity by 32.4 % and reduced the chain scission number by 22.2 % compared to that of control. The NaOCl was found to be the most effective for improving the delignification efficiency followed by PAA, they improved the delignification efficiency by 29.3 % and 27.3 %, respectively. The PAA improved the bleaching efficiency to a maximum of 39.9 % followed by 30.2 % with NaOCl.

Investigation of hydrolysis in poly(ethylene terephthalate) by FTIR-ATR

The hydrothermal aging of poly(ethylene terephthalate) (PET) was investigated at 70–95 °C. A new method to investigate the hydrolysis degree of PET by Fourier transform infrared spectroscopy (FTIR) was proposed. The spectra during the hydrothermal aging were measured using attenuated total reflection accessory (ATR). Peak resolving of carbonyl regions was performed, and the ratio of two groups of bands representing carboxylic acids and esters respectively were calculated to show the hydrolysis degree of ester groups in PET. The acid/ester ratio shows exactly the same trend as the average chain scission number per unit mass at various temperatures and thus can be used as a parameter to characterize the hydrolysis and random chain scission of PET. This method related to the hydrolysis mechanism directly, is simple, fast and convenient compared to the traditional methods such as viscometry, end-group titration and size exclusion chromatography (SEC). It may also be useful in hydrolysis characterization of other polyesters.

Hydrocarbons obtained by waste plastic pyrolysis: Comparative analysis of decomposition described by different kinetic models

Thermal degradation of waste polymers has been investigated in a batch reactor at temperatures of 410, 430 and 450°C using atmospheric pressure without catalysts. Raw materials were real wastes (plastics, paper, etc.), but considerably differences have been found among them. According to FTIR analysis raw materials contained polyethylene, polypropylene, polystyrene and polyamide 6. The composition of plastics (polyethylene, polypropylene, polystyrene, etc.) was different, however in case of one sample (W-3) significant motor oil content has been demonstrated. Different hydrocarbon fractions were produced in the cracking reactions: gases, pyrolytic oil and heavy oil. The polymer destruction was described based on different reaction kinetic approaches (yields of volatile products, theory of continuous distribution, and number of scissions per an average polymer chain) and reaction kinetic parameters (e.g. activation energy of the degradation) have been calculated then results were compared. The values obtained have also been compared to literature data and try to reflect the complexity of pyrolysis process. Pyrolysis reactions could be well described by the used models. The calculated results well approached the data obtained from the literature, but due to the difference in raw material composition, the calculated kinetic parameters have been different, too.

Which Controls the Depolymerization of Cellulose in Ionic Liquids: The Solid Acid Catalyst or Cellulose?

Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires--as the first-step--its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100 degrees C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented.

Kinetics of autocatalytic acid hydrolysis of cellulose with crystalline and amorphous fractions

The acid hydrolysis of cellulose with crystalline and amorphous fractions is analyzed on the basis of autocatalytic model with a positive feedback of acid production from the degraded biopolymer. In the condition of low acid rate production compared with hydrolysis rate, both fraction of cellulose decrease exponentially with linear and cubic time dependence, and the normalized number of scissions per cellulose chain follows a sigmoid behavior with reaction time. The model predicts that self generated acidic compounds from cellulose accelerate the degradation of the biopolymer. However, if the acidic compounds produced are volatile species, then their release under low pressure will reduce the global rate of degradation of cellulose toward its intrinsic rate value determined by the residual acid catalyst present in the starting material.

Approximate solution of the autocatalytic hydrolysis of cellulose

Depolymerization of cellulose in homogeneous acidic medium is analyzed on the basis of autocatalytic model of hydrolysis with a positive feedback of acid production from the degraded biopolymer. The normalized number of scissions per cellulose chain, S(t)/n° = 1 − C(t)/C0, follows a sigmoid behavior with reaction time t, and the cellulose concentration C(t) decreases exponentially with a linear and cubic time dependence, C(t) = C0exp[−at − bt3], where a and b are model parameters easier determined from data analysis.

Characterizing the influence of electron irradiation on scleroglucan

The electron irradiation effect on scleroglucans was investigated using different energy doses. Electron spin resonance spectra revealed radicals that were stable for several days. 1H NMR, 13C NMR and Raman spectra indicated no differences in chemical backbone structure due to irradiation. In contrast, lower viscosities of aqueous solutions were received at higher energy doses. This was caused by polymer degradation. The irradiation also decreased the weight average molar masses observed by gel permeation chromatography and multi-angle light scattering. Beginning from raw materials exceeding 4 · 10 6 Da, a number of main chain scissions of approximately 0.3 · 10 −7 mol J −1 was found. But for one scleroglucan quality the scission number decreased with higher doses. In addition, the characterization via asymmetrical flow field-flow fractionation proved the presence of low and high molar mass fractions. The electron irradiation led to a preferred scission of the high molar mass chains and increased the lower molar mass fraction. Due to this effect, the broadness of the molar mass distribution decreased.

On the degradation evolution equations of cellulose

Cellulose degradation is usually characterized in terms of either the chain scission number or the scission fraction of cellulose unit as a function of degree of polymerisation (DP) and cellulose degradation evolution equation is most commonly described by the well known Ekenstam equations. In this paper we show that cellulose degradation can be best characterized either in terms of the percentage DP loss or in terms of the percentage tensile strength (TS) loss. We present a new cellulose degradation evolution equation expressed in terms of the percentage DP loss and apply it for having a quantitative comparison with six sets of experimental data. We develop a new kinetic equation for the percentage TS loss of cellulose and test it with four sets of experimental data. It turns out that the proposed cellulose degradation evolution equations are able to explain the real experimental data of different cellulose materials carried out under a variety of experimental conditions, particularly the prolonged autocatalytic degradation in sealed vessels. We also develop a new method for predicting the degree of degradation of cellulose at ambient conditions by combining the master equation representing the kinetics of either percentage DP loss or percentage TS loss at the lowest experimental temperature with Arrhenius shift factor function.

Effects of gamma irradiation on PMMA/polyaniline nanofibre composites

Polyaniline (PANI) presents promising antioxidant and radical-scavenging properties. Substances having these characteristics are good candidates for radioprotecting agents. In this work, nanofibres of polyaniline emeraldine doped with (?)-camphor-10-sulfonic acid (PANI-(?)-CSA) were prepared by self-assembly method under 'silent' and sonochemical conditions. PANI emeraldine base (PANI-EB) nanofibres were obtained after dedoping with NH4OH and were used as additives in films of commercial PMMA, in order to investigate radiostabilising effects on the PMMA matrix. Films containing aniline (An) and PANI-EB grains were also prepared for comparison. Variations in viscosity-average molar mass (Mv) at a 25 kGy dose showed that samples containing aniline, PANI-EB nanofibres or grains in amounts of 0.15% (wt/wt) underwent less degradation than the control sample. In addition, PMMA/PANI-EB nanofibres and PMMA/An at 0.15% (wt/wt) showed a smaller number of scissions per original molecule (α) than control samples in the 25?75 kGy dose range. Spectroscopic characterisation (FTIR, UV-Vis) and scanning electron microscopy (SEM) of PANI samples were also performed.

Construction of a polymer skeleton that is cut in half by ionizing radiation

AbstractPolystyrene with a benzyl ester of carboxylic acid at the center of a polymer skeleton was synthesized by living radical polymerization. The initiator used had two functional groups for 2,2,6,6‐tetramethylpiperidinoxyl (TEMPO)‐mediated living radical polymerization on the benzyl and the carboxylic sides of the benzyl ester. Introduction of the benzyl ester changed the polystyrene from a crosslink type to a scission type polymer on γ‐irradiation. Irradiation of the polymer resulted in a binary change of the molecular weight because of the dissociative capture of secondary electrons by the benzyl ester, as: The binary change of the molecular weight suggests that the polymer can be used as a new type of radiation resist with high sensitivity and spatial resolution to ionizing and high resistivity to plasma etching. The number of scissions per 100 eV radiation energy absorbed was 0.29, which was about one fourth of the yield of secondary electrons. The low efficiency was because of the recombination of polymer radicals generated by the dissociative electron attachment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1068–1075, 2005

Radiolytic degradation of poly(vinyl chloride) systems

We examined the gamma radiation effects on PVC plasticized with di(2-ethylhexyl)phthalate (DEHP), diisobutyl phthalate, trioctyl trimellitate and Viernol ®, as well as its effect on PVC plasticized with DEHP and stabilized with Tinuvin P ®. The PVC samples were analysed, before and after irradiation at different doses, by UV spectroscopy, viscometry and mechanical testing. A multivariate statistical analysis was carried out on five properties: tensile strength, percent elongation, number of scissions per chain, viscosity-average molecular weight and UV-visible absorbance. The scores from a principal component analysis (PCA) of the non-stabilized samples show that the PVC/DEHP samples were the most degraded by chain scission upon irradiation, especially at the 25 and 60 kGy dosages, while the 400 nm absorbance, associated with film yellowing, remained relatively unchanged for these samples. For the other three systems, degradation by chain scission is smaller, and the UV absorbance is more dependent on radiation dosage. For the PVC/DEHP samples, the addition of Tinuvin P ® significantly decreases the number of scissions per chain, especially at 25 and 60 kGy irradiation doses.

Radiolytic degradation and stabilization of poly(vinyl chloride)

Medical products, food packaging and pharmaceutical products all made with poly(vinyl chloride) (PVC) can suffer degradation when they go through sterilization by gamma radiation. Stabilizing additives are used to minimize the degradation of this polymer. These additives act by substituting irregular structures such as the allylic chloride atom in the PVC by stable structures, thus retarding the radiolytic degradation of the polymer. In this study we looked at the radiolytic degradation in films of PVC plasticised with DEHP and stabilized with Tinuvin P, by viscometry, mechanical properties and ultraviolet-visible absorption spectroscopy. The variation of the number of scissions per chain, studied by viscometry showed efficiency in the stabilized polymer. The results showed an excellent protection of scission degradation of the chain attributed to the stabilizer, with a maximum protection of 90% at a concentration of 0.5% Tinuvin P, as well as the improvement of the mechanical properties when the polymer is subjected to different doses of radiation.

Relaxation behavior of polymers probed by positron annihilation lifetime spectroscopy

Relaxation behaviors of polyethylene, polypropylene, and polycarbonate have been studied by positron annihilation lifetime spectroscopy (PALS). In PALS positron sources made of radioisotopes are used to inject positrons into polymer as a micro probe. The injected positron probes can induce radiation effect, which plays an important role in detecting the polymer relaxation behavior through electrons trapped in shallow potentials at low temperature. Monitoring the intensity (I3) of orthopositronium (o-Ps), transitions of γ and δ relaxation can be measured by PALS as a secondary effect. In this experiment, the change of I3 below Tg is connected with the number of the trapped electrons, which can be excited from the shallow potential by the thermal motion of polymer structures and visible light irradiation. In the PALS measurements of non-irradiated PP samples, relaxation of methyl groups was observed as low as 50 K, which can be assigned as the δ relaxation. Relaxations of β and γ were also observed for the non-irradiated PP samples between 100–370 K. However for the 3 MGy Y-ray irradiated PP samples, only β relaxation was observed because the large radiation dose caused a large number of scissions of -CH3 groups from main chains and the characteristics changed. For the irradiated samples, radiation hardening was observed.

Cellulose protection during ozone treatments of oxygen delignified Eucalyptus kraft pulp

Various totally chlorine-free sequences with a Z stage (XOZP, XOAZP, XOZRP, and XOAZRP) were implemented with a view to examining the individual and combined effects of using an additive (A), consisting of oxalic acid and a post-treatment (R) based on sodium borohydride on the properties of the resulting pulp and effluents. The performance of the reagents was analyzed through the study of: chain scission number in the cellulose chain; selectivity and efficiency of the process; crystallinity and carbohydrates composition of the pulps. Finally, the pulp, paper and effluents properties of the sequence including both treatments (XOAZRP) were compared with an ECF sequence of the XODPD type. The results were highly favorable.