Decrease In Molar Mass Research Articles

Degradation of trans‐polyisoprene after root filling with thermoplasticized techniques

To evaluate ex vivo degradation of gutta-percha following six thermoplastic obturation techniques. Ninety human-extracted mandibular premolars were selected and divided randomly into nine groups for filling. Group 1: thermomechanical compaction for 3 s with Konne gutta-percha points (Konne Ind. e Com. de Mat. Odontol., Belo Horizonte, MG, Brazil); Group 2: thermomechanical compaction for 3 s with Dentsply TP gutta-percha points (Dentsply Indústria e Comércio Ltda, Petrópolis, R.J. Brazil); Group 3: thermomechanical compaction for 10 s with Konne; Group 4: thermomechanical compaction for 10 s with Dentsply TP; Group 5: warm vertical condensation using System B (EIE/Analytic, Richmond, WA, USA) with Konne; Group 6: warm vertical condensation using System B with Dentsply TP; Group 7: vertical condensation with Konne; Group 8: vertical condensation with Dentsply TP; Group 9: Microseal cone (Analytic Endodontics, Glendora, CA, USA). A further four groups were assessed without using teeth, Group 10: Microseal microflow (Analytic Endodontics); Group 11: Obtura (Obtura Corporation, Penton, MO, USA); Group 12: Obtura flow (Obtura Corporation); Group 13: Thermafil (Dentsply Maillefer, Tulsa, OK, USA). The filling material was removed from the root canal and trans-1,4-polyisoprene isolated by solubilization of the root filling remnants in chloroform followed by filtration and centrifugation. By gel permeation chromatography and infrared spectroscopy, the occurrence and degree of degradation were assessed. The results were analysed statistically using the Kruskal-Wallis test. With differential scanning calorimetry, the thermal behaviour of the gutta-percha was determined. A significant decrease in polymer molar mass and the production of carboxyl and hydroxyl groups in the polymer were observed with thermomechanical compaction used for 10 s and vertical condensation filling techniques (P = 0.0001 and P = 0.0005, respectively). Other techniques caused no polymer degradation. Polyisoprene degrades with high temperature. Thermomechanical compaction for 10 s and vertical condensation were associated with the greatest degradative process.

Alkyl methacrylate and styrene terpolymers as lubricating oil viscosity index improvers

The properties of styrene/dodecyl methacrylate/octadecyl methacrylate terpolymers as viscosity index improvers of lubricating mineral oils were investigated. Terpolymers of different composition and molar mass were prepared by peroxide-initiated polymerization of the monomer mixture in a mineral base oil solution. All the terpolymer solutions in base oil exhibited high kinematic viscosity and viscosity index values (> 130), proving their high thickening efficiency. The ratio of viscosity values at 100°C and 40°C of styrene/alkyl methacrylate additive solutions was between 0.95 and 1.0, showing the coherent thickening effect in a wide temperature range, comparable with pure alkyl methacrylate additives. Increasing content of styrene in the additive and decreasing molar mass of the terpolymer resulted in a decrease in viscosity and viscosity index while the shear stability increased. The obtained results give guidelines for optimization of the terpolymers composition and structure in order to assure the best lubricant application properties.

On the solid-state ageing behaviour of the polysaccharide, guar gum

Dilute solution viscometry was used to explore the effect of solid-state ageing on the interactions that occur between guar gum and water. The resulting data set, derived from nearly 700 independent experiments, led to a value for the Flory–Huggins interaction parameter, χ, of 0.56 ± 0.12. This value, which appeared independent of ageing, is in good agreement with the majority of published data. The effect of ageing on molar mass was also explored, using Mark–Houwink–Sakurada (MHS) theory. Absolute molar mass values were found to depend sensitively on the choice of MHS constants, but the effect of ageing was unequivocal; under all conditions, it resulted in a pronounced decrease in molar mass. In concert, these results strongly suggest that, in guar, solid-state ageing reactions are largely associated with scission of the molecular backbone. This hypothesis was then tested by infra-red and Raman spectroscopy. Although infra-red spectroscopy did reveal some subtle differences between the spectra of guar and locust bean gum (LBG), a related polysaccharides with a different galactose:mannose ratio, no equivalent effects were seen in aged guar. However, clear differences between the Raman spectra of guar and LBG were seen, demonstrating that the technique is well capable of revealing changes in galactose:mannose ratios. Examination of aged guar samples revealed no comparable effects, reinforcing the notion that, in this polysaccharide, chain scission reactions dominate such that solid-state ageing does not lead to changes in the nature of its interaction with water.

Clinical relevance of trans 1,4-polyisoprene aging degradation on the longevity of root canal treatment

This in vivo study investigated the time of degradation of root filling material (trans 1,4-polyisoprene) retrieved from endodontically treated teeth and correlated the occurrence of degradation with the longevity of endodontics. Thirty-six root-filled teeth with different filling times (2 to 30 years) and with and without periapical lesions were selected. All teeth presented clinical indication for root canal retreatment. The association among filling time, presence of periapical lesion and root filling material degradation was investigated. Root filling samples were retrieved from the root canals using a Hedströ m file without solvent. The trans 1,4-polyisoprene was isolated by root filling solubilization in chloroform followed by filtration and centrifugation. GPC and FT-IR were the analytical techniques utilized. Degradation of trans 1,4-polyisoprene occurred with time, as a slow process. It is an oxidative process, and production of carboxyl and hydroxyl groups in the residual polymer were observed. Statistically significant decrease of molar mass was observed after 5 (p=0.0001) and 15 (p=0.01) years in teeth with and without periapical lesion, respectively. Bacteria participated in polymer degradation. Gutta-percha aging was proven an important factor for the long-term success of endodontic treatment. The findings of the present study showed that, after 15 years, polymer weight loss may decrease the capacity of the filling mass to seal the root canal space and prevent re-infection, thus compromising significantly the longevity of root canal therapy.

Degradation of trans‐polyisoprene over time following the analysis of root fillings removed during conventional retreatment

To evaluate in vivo degradation of root filling materials over time. Thirty-six root filled teeth with or without periapical lesions were selected. Teeth with poor coronal restoration were not included. The teeth had been root filled 3-30 years previous and were scheduled for conventional retreatment. The association of root canal treatment, age, periapical lesion and root filling degradation was investigated. The filling material was removed from the root canal using files and no solvent. Trans-1,4-polyisoprene was isolated through solubilization of root filling remnants in chloroform followed by filtration and centrifugation. Gel permeation chromatography (GPC) and infrared spectroscopy (FT-IR) were utilized to study the occurrence and degree of degradation. The GPC and FT-IR data were collected for each sample and analysed statistically using the Kruskal-Wallis test. Degradation of trans-1,4-polyisoprene was a slow process. The process was identified as an oxidation reaction through the production of carboxyl and hydroxyl groups. Compared with the control group, significant molar mass decrease was noted after 15 years (P = 0.0146) in teeth with no periapical lesions. However, in teeth associated with periapical lesions the number of years for significant degradation was reduced to 5 (P = 0.0009). Polyisoprene degrades inside root canals as an oxidative process. The presence of periapical lesions was associated with a more rapid onset of degradation.

Modeling non-Gaussian extensibility effects in elongation of nearly monodisperse polystyrene melts

Elongational viscosity and birefringence of two nearly monodisperse polystyrene melts with molar mass MW of 206000gmol−1 (PS206k) and 465000gmol−1 (PS465k), respectively, were measured simultaneously by Luap et al. [Rheol. Acta. 45, 83–91 (2005)]. The samples did not follow the stress optical rule (SOR). Elongational viscosity data can be modeled quantitatively by the molecular stress function (MSF) model of Wagner et al. [J. Rheol. 49, 1317–1327 (2005)], which is based on the assumption of a strain-dependent tube diameter and the interchain pressure term of Marrucci and Ianniruberto [Macromolecules 37, 3934–3942 (2004)], and which is modified here to account for non-Gaussian chain extension using the Padé approximation of the inverse Langevin function. The tube diameter relaxation time scales with MW2. While the transient elongational viscosity shows a small dependence on finite extensibility, the predicted steady-state elongational viscosity is not affected by non-Gaussian effects. The power-law exponent of the relation between steady-state elongational stress and Deborah number predicted is found to be 0.59 for PS465k, confirming a previous result of 0.6 for a similar molecular mass sample [Wagner et al. (2005)]. The power-law exponent is invariant with respect to temperature but slightly dependent on molar mass, thereby increasing with decreasing molar mass. Deviations from the SOR are described quantitatively by the MSF model by taking into account finite chain extensibility, and within the experimental window investigated, deviations from the SOR are predicted to be strain rate-, temperature-, and molar mass independent, in good agreement with experimental data.

In vivo aging of gutta‐percha dental cone

AbstractGutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 105 to 1.7 × 105 g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 104 g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006

Gamma irradiation effects on poly(hydroxybutyrate)

Brazilian poly(hydroxybutyrate), PHB, as well as its copolymer, poly(hydroxybutyrate- co-valerate), P(HB- co-HV), containing 6.3 mol% of valerate, were irradiated with γ radiation ( 60Co) at ambient temperature and in the presence of oxygen. The viscosity-average molar mass ( M v) was analyzed by the viscosity technique using an Ostwald-type capillary viscometer. The polymers showed a decrease in molar mass with the increase in dose, reflecting the scissions that occurred at random in the main chain. The value G (scissions/100 eV of energy transferred to the system) and the parameter α (scissions per original molecule) were also obtained by the viscosity technique. The melting temperature ( T m) was determined by differential scanning calorimetry (DSC) and showed a decrease with increasing irradiation dose. Analyses of DSC also revealed double endothermic peaks, associated with the polymorphic transitions, which became a single peak with increased dose. Thermogravimetry analysis (TGA) revealed small differences between the decomposition temperatures of the irradiated and non-irradiated samples. The degree of crystallinity of PHB samples, on the other hand, which were obtained by the DSC and X-ray diffraction techniques, increased with the irradiation dose. Changes in the lattice parameter of the irradiated samples and in the size of the crystallites were also observed by X-ray diffraction. The samples used in this work did not pass through any purification process and were analyzed in powder form, exactly as they arrived from the factory.

Homogenization-induced degradation of hydrophobically modified starch determined by asymmetrical flow field-flow fractionation and multi-angle light scattering

High-pressure homogenization of modified starches is a type of treatment used within the food and pharmaceutical industry for the production of emulsions. Such intense mechanical treatment may, however, influence the size and size distribution of the starch polymer, which may affect the properties of the emulsions. In this work, asymmetrical flow field-flow fractionation (AsFlFFF) connected on-line to a multi-angle light scattering detector (MALS) was used to study the influence of high-pressure homogenization upon molar mass and root-mean-square (r.m.s.) radius of three different octenyl succinate anhydride (OSA) starch samples originating from potato. The homogenization at constant pressure resulted in a significant decrease of both molar mass and r.m.s. radius. The magnitude of the change in molar mass and r.m.s. radius could be correlated to the initial size of the OSA starch and the energy dissipation rate of the homogenization treatment.

PET recycling: Evaluation of the solid state polymerization process

AbstractMany studies have been carried out to make bottle‐to‐bottle recycling feasible. One of the difficulties found is the decrease in the polymer's molar mass, which damages the injection blow molding process. A method usually employed to increase the molar mass of virgin PET consists of solid‐state polymerization (SSP). In this work, we studied the SSP process applied to post‐consumer recycled PET by analyzing the inherent viscosity and amount of carboxylic end groups, and the results of dynamic flow rheometry. Although the results show that the recycling process decreases polymer molar mass, and this indicates degradative processes, SSP was successful in increasing molar mass in post‐consumer recycled PET. This made feasible bottle‐to‐bottle recycling. In addition, the parallel plate rheometry technique was powerful in assessing the degradative process and, therefore, that the SSP process was successful. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Rheological properties of branched polystyrenes: nonlinear shear and extensional behavior

Nonlinear shear and uniaxial extensional measurements on a series of graft-polystyrenes with varying average numbers and molar masses of grafted side chains are presented. Step-strain measurements are performed to evaluate the damping functions of the melts in shear. The damping functions show a decreasing dependence on strain with an increase in mass fraction of grafted side chains. Extensional viscosities of the melts of graft-polystyrenes exhibit a growing strain hardening with increasing average number of grafted side chains as long as the side branches have a sufficient molar mass to be entangled. Graft-polystyrenes with side arms below the critical molar mass M c for entanglements of linear polystyrene but above the entanglement molar mass M e of linear polystyrene (M e < M w,br < M c) still show a distinct strain hardening. With decreasing molar mass of the grafted side chains (M w,br < M e) the nonlinear-viscoelastic properties of the graft-polystyrene melts approach the behavior for a linear polystyrene with comparable polydispersity.

Influence of Secondary Components on the Synthesis of Self-Cross-Linked N-Isopropylacrylamide Microgels

This work presents systematic studies of cross-linker-free microgels formed by copolymerization of N-isopropylacrylamide (NIPAAm) and various secondary monomer components in water under standard reaction conditions. The sizes, solid densities, and volume phase transitions of these particles have been characterized through static and dynamic laser light-scattering experiments. We find that introducing a hydrophobic component, for example, styrene (St) or methyl methacrylate (MMA), leads to particles with smaller sizes and higher solid densities, while the volume phase transition shifts to lower temperatures. On the other hand, introducing a hydrophilic component such as acrylamide (AAm) or acrylic acid (AA) leads to larger particles with lower solid densities and a volume phase transition that shifts to higher temperatures and is broadened. The molar mass changes little in either case. Introducing a charged component such as sodium styrene sulfonate (NaSS) or poly(sodium styrene sulfonate) (PNaSS) leads to a sharp decrease in molar mass and particle size, and a very broad phase transition. These trends provide good guidance for synthesizing both self-cross-linked and cross-linked copolymerized microgels of different properties.

Degradation of unstabilised polypropylene and a propene- 1-pentene copolymer

Abstract The degradation of polypropylene (PP) and a propene-1-pentene copolymer (P2) have been monitored with regard to chemical composition, molar mass distribution and chemical composition distribution. The increase in the carbonyl index can be monitored by IR and a decrease in molar mass can be observed from size-exclusion chromatography (SEC). CRYSTAF shows that the chemical heterogeneity of the samples broadens with continuing degradation. SEC-FTIR reveals that the degraded species are mainly found in the low-molecular-weight end of the molar mass distribution. Spatial heterogeneity of the degradation process has been proven by the analysis of abrased layers. It was found that the P2 copolymer degrades at a higher rate compared to PP.

Effects of hygrothermal aging on the molar mass and thermal properties of recycled poly(ethylene terephthalate) and its short glass fibre composites

This paper reports on the effects of hygrothermal aging at 70 °C in water, and at 80% relative humidity, on the molar mass and thermal properties of recycled poly(ethylene terephthalate) and its short glass fibre composites. During the initial period of exposure, water uptake increases linearly with the square root of time and apparent diffusivity decreases as fibre content increases and as relative humidity decreases. Samples exposed to 80% RH reach an equilibrium water content, while samples immersed in water do not. Composites absorb more water than expected on the basis of matrix sorption behaviour, thus suggesting that other mechanisms, like capillarity and/or transport by microcracks, are active. The observed molar mass decrease has been successfully modelled as a pseudo first-order reaction whose rate constant depends on the humidity conditions. Due to a chemicrystallization process the crystallinity of rPET and its composites increases during aging. The glass transition temperature, as measured on the second DSC scan, depends on the number-average molar mass reached during hygrothermal aging.

Functionalization of polyethylene/silane copolymers in posttreatment reactions

Abstract7‐Octenyldimethylphenylsilane was copolymerized with ethylene via Et(Ind)2ZrCl2 methylaluminoxane catalyst system without loss of catalyst activity or decrease in molar mass. The comonomer contents in the polymer samples were at a level of 0.15–1.0 mol % and the reactive phenylsilane groups were posttreated to different alcoxy‐ and halosilane groups, for example, SiF, SiCl, SiOCH3, and SiOCH2CH3. The posttreatment reactions had no major effect on the molar masses or on the thermal properties (measured with differential scanning calorimetry) of the copolymers. The reaction pathways were nearly independent of the comonomer contents and the reactions reached 70–100% conversions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1461–1467, 2004

Purification of xylose reductase from Candida mogii in aqueous two-phase systems

Xylose reductase (XR) from Candida mogii was extracted by partitioning in aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) and phosphate salts. An experimental design was used to evaluate the influence of the variables molar mass of PEG ( A), concentration of PEG ( B), concentration of phosphate ( C), and concentration of NaCl ( D) on XR extraction. The positive effect of variable B and the negative effect of A and of the interaction between A and B on the purification factor in the top phase (PF T) indicated that a simultaneous increase in PEG concentration with a decrease in molar mass of PEG leads to an increase in that response. Phosphate concentration also had a negative effect, indicating an increase in PF T with a decrease in its value. A linear model fitted to the data indicated the need to change the ranges of the variables. In a second experimental design, the influence of a lower range of PEG molar mass (MMPEG) and of tie-line length (TLL) on the partitioning of XR was studied. Quadratic models were predicted for the responses purification factor in the top phase and XR yield in the top phase ( Y T), and the maximum values predicted by these models were 1.59±0.40 and 105.8±26.2%, respectively. A 19-fold increase in the selectivity factor was experimentally achieved for a system with PEG 1000 and TLL 34. The k, PF T and Y T values corresponding to 21.21, 1.89 and 103.5 respectively were also obtained under these experimental conditions.

Effect of Ozonation on Assembly of Xylans

Summary In this study the molecular structure of birch xylan was altered by ozonation. Longer ozonation times increased the cleavage of aromatic rings in the lignin residues attached to the xylan molecules, resulting in the formation of muconic acid derivatives and other carboxylic acid structures. Size exclusion chromatography showed a decreasing molar mass of xylan after ozonation. The ozonation improved xylan solubility as evidenced by the reduced amounts of aggregates in aqueous solution. Atomic force microscopy showed increases in the sizes of the aggregates. Furthermore, the ozonation resulted in a decreased ability of xylan to assemble into particle-like structures on cellulose surfaces. We therefore believe that there is a relationship between xylan aggregation in aqueous solution and the formation of xylan surface structures on cellulose.

Rheological and calorimetric properties of recycled bisphenol A poly(carbonate)

Mechanical recycling of engineering polycarbonate wastes provides an interesting way to decrease the impact on environment, if the degradation due to successive processing is properly characterized. We analyzed polycarbonate (PC) degradation generated by eight successive recycling, using rheological, calorimetric and colorimetric tools at each step. From the first to the fifth recycling, an increase of storage modulus E′ (at T=30 °C and f=1 Hz) in both bending and tension mode is observed, together with a decrease of the Newtonian limit viscosity η 0 (at T=240 °C and γ ̇ =0.1 s −1). Moreover, a decrease of T g of about 3.5 °C and of Δ C p at T g is noticed from the first to the eighth recycling. Accelerated aging under UV irradiation shows a more rapid coloration of recycled PC. All these results evidence a decrease of molar mass resulting from thermomecanical stress encountered by the PC during recycling. This modification of polycarbonate properties, which remaining good, must be taken into account to adjust the processing conditions and determine the possible applications.

Effect of Melt Processing on Crystallization Behavior and Rheology of Poly(3-hydroxybutyrate) (PHB) and its Blends

Poly(3-hydroxybutyrate) (PHB) is sensitive to high processing temperatures. This leads to a decrease in molar mass as well as a lower melt viscosity. The crystallization temperature shifts to lower values, and crystallization kinetics is slow. A mixture was developed in order to improve the manufacturing properties and the final product. The blends exhibit a slight reduction in molar mass because they have a lower melting point than pure PHB, and can be extruded at their melt temperature of 170 to 180°C. Then they immediately crystallize at 125 to 100°C. Differential scanning calorimetry (DSC) shows the effect of holding time in the melt on crystallization behavior. It has been shown that the crystallization time has to be longer in the case of PHB and shorter for the blends. Thermal degradation of PHB and its blends has been investigated using thermogravimetry analysis (TG). Derivative thermogravimetry coupled with TG (TG/DTG) curves show three decomposition stages for blends at 290, 340 and 445°C, respectively. Acetic acid, water, carbon dioxide and methane are produced by degradation at a higher temperature.

Polypropylene compounding with post-consumer material: II. Reprocessing

We have investigated extrusion moulding for 13 processing cycles, using formulations containing virgin polypropylene and 1:1 mixtures of virgin and post-consumer polypropylene containing, or not, the antioxidant Recyclostab 411™. The main effect of reprocessing for polypropylene was the decrease of molar mass due to degradation with chain scission, which was detected by the melt flow rate and the increase in crystallinity. Antioxidant consumption and material stability reduction with processing cycles were observed by the reduction of the thermo-oxidative stability detected by oxidative induction time measurements. The addition of antioxidants minimized degradation and maintained the stability of the material.