Reduction In Molar Mass Research Articles

Study of negative substitution and monomer self‐condensation effects on molar mass and structural characteristics of hyperbranched polyesters originating from a high‐functionality core

AbstractIn order to provide more insight into the effect of core functionality on hyperbranched polymer characteristics, two series of hyperbranched polyesters (HBPEs) were synthesized by reacting 2,2‐bis(methylol)propionic acid (bis‐MPA) as AB2 monomer with both dipentaerythritol (DPE) and pentaerythritol as six (B6)‐ and four (B4)‐functional core molecules. The molar mass, composition and structure of HBPEs were determined with respect to the negative substitution logic and monomer self‐condensation effect. The molar masses and structures of HBPEs containing DPE core were less influenced by the negative effect of a reacted hydroxyl group on the reactivity of other hydroxyl groups in the same monomer unit. Thus, the use of DPE core in copolymerization with bis‐MPA monomer could help slightly to increase the molar mass of HBPEs. Conversely, the effect of self‐condensation of bis‐MPA on the molar mass reduction was more pronounced in the case of DPE hyperbranched polymers due to the A–B negative substitution effect. These two effects become more significant with increasing pseudo‐generation numbers of the HBPEs. © 2014 Society of Chemical Industry

Influence of melt processing conditions on poly(lactic acid) degradation: Molar mass distribution and crystallization

The degradation of poly(lactic acid) (PLA) during thermal–mechanical processing was studied and the influence of processing conditions on degradation rate was determined by size exclusion chromatography coupled with multi-angle light scattering (SEC–MALS). A two-parameter model accounting for both chain scission and recombination processes was used to describe the experimentally observed molar mass distribution. The degradation and recombination rate constants were determined for undried and dried PLA. It was highlighted that the effect of processing temperature (in the 170–210 °C range), processing time (until 30 min) and shear rate (rotor speed varying from 0 to 150 rpm) on molar mass reduction can be relatively well simulated insofar as self-heating related to the mechanical energy conversion into heat was taken into account.The influence of melt processing on the thermal behaviour of PLA was also investigated using temperature modulated differential scanning calorimetry (TMDSC). It was evidenced that the molar mass reduction affects the crystallizability of PLA. Cold crystallization temperature progressively decreases with decreasing molar mass and the metastable α' phase is formed in place of the stable α phase. The α′ phase can be partially converted into α form during melting giving rise to a double-melting peak. The two peaks can be separated using reversing and non-reversing signals confirming that recrystallization of the α′ form occurs.

Modelling of PLA melt rheology and batch mixing energy balance

A method to determine the overall energy balance of neat PLA processing in a batch mixer was proposed. Energy consumption calculations rely upon shear rate and viscosity calculations using a double-Couette approximation. In the case of PLA mixing, it was found that the energy consumption is increased with an increasing rotor speed and decreased with an increasing temperature. During the melting phase the energy consumption is not strongly affected by the process parameters and the energy efficiency is close to 1. During the mixing phase, for a given viscosity, the energy efficiency is increased with increasing rotor speed or temperature and a method to optimise the process parameters to obtain a low viscosity with limited degradation and high energy efficiency was proposed. Moreover a comparison is given between the double-Couette approximation and conventional rheometry (rotational and capillary). Conventional rheometry translates into an overestimation of the viscosity especially at low temperature. This overestimation could probably be explained by the high sensitivity of rheology to molar mass reduction.

Network formation of graphene oxide in poly(3-hydroxybutyrate) nanocomposites

Network formation of graphene oxide (GO) nanoplatelets was held accountable for the modification of the rheological properties of nanocomposites based on poly(3-hydroxybutyrate) (PHB). The nanocomposites were prepared by a casting procedure from the green solvent γ-butyrolactone. The nature of the GO network and percolation limits were analyzed by making use of the molar mass reduction of PHB that takes place in the melt, as well as by studying the deformation dependence of the viscoelastic behavior of the nanocomposites. The percolation volume fraction for the formation of GO network was found to be below 0.07%, while a corresponding GO aspect ratio of 400 was determined. The equilibrium shear modulus (|Geq*|) of the GO network and the critical strain γc of the nanocomposites could be described both by a power-law dependence on the volume fraction of GO nanoparticles. Further assessment of the structure formation of the GO nanoparticles was made in the solid state, wherein the shear modulus of GO was analyzed with the Halpin–Tsai model. The values thus determined suggested the existence of tiled nanoplatelets within the formed network structure in the nanocomposites. The thermal properties of the nanocomposites were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The microstructure of the samples was also characterized using X-ray diffraction (XRD) measurements.

Assessing changes on poly(ethylene terephthalate) properties after recycling: Mechanical recycling in laboratory versus postconsumer recycled material

Keeping rheological, mechanical and thermal properties of virgin poly(ethylene terephthalate), PET, is necessary to assure the quality of second-market applications. A comparative study of these properties has been undertaken in virgin, mechanical recycled and commercial recycled PET samples.Viscoelastic characterization was carried out by rheological measurements. Mechanical properties were estimated by tensile and Charpy impact strength tests. Thermal properties and crystallinity were evaluated by differential scanning calorimetry and a deconvolution procedure was applied to study the population of the different crystals. Molecular conformational changes related to crystallinity values were studied by FTIR spectroscopy. Variations in average molecular weight were predicted from rheology. Besides, the presence-absence of linear and cyclic oligomeric species was measured by mass spectrometry techniques, as MALDI-TOF.Mechanical recycled PET undergoes a significant decline in rheological, mechanical and thermal properties upon increasing the number of reprocessing steps. This is due to the cleavage of the ester bonds with reduction in molar mass and raise in cyclic oligomeric species, in particular [GTc]n and [GTc]n-G type. Chain shortening plus enrichment in trans conformers favour the crystallization process which occurs earlier and faster with modification in crystal populations. Additional physicochemical steps are necessary to preserve the main benefits of PET.

Abrasion and fatigue resistance of PDMS containing multiblock polyurethanes after accelerated water exposure at elevated temperature

Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers (PDMS-urethanes). Two commercially available examples, PurSil 35 (denoted as P35) and Elast-Eon E2A (denoted as E2A), were evaluated for abrasion and fatigue resistance after immersion in 85 °C buffered water for up to 80 weeks. We previously reported that water exposure in these experiments resulted in a molar mass reduction, where the kinetics of the hydrolysis reaction is supported by a straight forward Arrhenius analysis over a range of accelerated temperatures (37–85 °C). We also showed that the ultimate tensile properties of P35 and E2A were significantly compromised when the molar mass was reduced. Here, we show that the reduction in molar mass also correlated with a reduction in both the abrasion and fatigue resistance. The instantaneous wear rate of both P35 and E2A, when exposed to the reciprocating motion of an ethylene tetrafluoroethylene (ETFE) jacketed cable, increased with the inverse of the number averaged molar mass (1/Mn). Both materials showed a change in the wear surface when the number-averaged molar mass was reduced to ≈16 kg/mole, where a smooth wear surface transitioned to a ‘spalling-like’ pattern, leaving the wear surface with ≈0.3 mm cracks that propagated beyond the contact surface. The fatigue crack growth rate for P35 and E2A also increased in proportion to 1/Mn, after the molar mass was reduced below a critical value of ≈30 kg/mole. Interestingly, this critical molar mass coincided with that at which the single cycle stress–strain response changed from strain hardening to strain softening. The changes in both abrasion and fatigue resistance, key predictors for long term reliability of cardiac leads, after exposure of this class of PDMS-urethanes to water suggests that these materials are susceptible to mechanical compromise in vivo.

Increase of long-chain branching by thermo-oxidative treatment of LDPE: Chromatographic, spectroscopic, and rheological evidence

Low-density polyethylene was thermo-oxidatively degraded at 170 °C, i.e., degraded in the presence of air, by a one thermal cycle (1C) treatment during times between 30 and 90 min, and by a two thermal cycles (2C) treatment, i.e., after storage at room temperature, an already previously degraded sample was further degraded during times between 15 and 45 min. Characterization methods include gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, as well as linear and nonlinear rheology. A reduction of molar mass was detected for all degraded samples by GPC, as well as an increase of the high molar mass fraction of the 1C sample degraded for the longest time. Intrinsic viscosity measurements indicate also a reduction of molar mass with increasing degradation times for both 1C and 2C samples. Thermo-oxidation is confirmed for 1C and 2C samples by analyzing specific indices in FTIR. Linear viscoelasticity seems to be in general only marginally affected by thermo-oxidative exposure, while the enhanced strain-hardening effect observed in uniaxial extension experiments presents a clear evidence for an increased long-chain branching (LCB) content in both 1C and 2C samples. Elongational viscosity data were analyzed by the molecular stress function (MSF) model as well as the Wagner-I model, and for both models, quantitative description of the experimental data for all samples was achieved by fit of only one nonlinear model parameter. Time-deformation separability was confirmed for all samples degraded, 1C as well as 2C, for cumulative degradation times of up to 90 min. The characterization by GPC was confronted with the characterization obtained from nonlinear rheology. It can be stated that elongational rheology is a powerful method to detect structural changes due to thermo-oxidative degradation, especially the formation of enhanced LCB. It has the further advantage that experimental data can be quantified by a single nonlinear model parameter of constitutive equations like the MSF or the Wagner-I model.

Comparative thermal, biological and photodegradation kinetics of polylactide and effect on crystallization rates

A comparison is made between available literature and present results of the three major types of polylactide (PLA) degradation giving a compiled view on the details of degradation mechanisms with relation to explicit factors affecting degradation. The temporal decrease of molar mass has been analyzed under isothermal conditions at 220 °C, biological and photodegradation conditions using a polylactide (PLA) with ∼4 mol% D units. The decrease of molar mass with time during biodegradation follows a first order process (M = Moe−kt) while the molar mass of specimens tested during thermal and photodegradation follows a second order law (1/M = (1/Mo) + kt) Literature data obtained in similar degradation conditions were also adequately fitted with these equations. This allows us to conclude that the main step in the three types of degradation is a random chain excision, with some differences in the algebraic functionality. Under the degradation conditions tested, the degradation rate follows the progression thermal > photo > biological. For equivalent molar mass, the effect of degradation type on cold crystallization and melting is significant indicating that degradation cannot be explained by a solely outcome of chains breakage and molar mass reduction. This feature is especially prominent when the linear growth rates of specimens subjected to bio or photo degradation are compared. Anhydride groups that are formed during photodegradation decrease the crystallization rate compared to biodegraded specimens of equivalent molar mass. The molar mass dependence of the maximum growth rate follows a power law with exponents 1.3 for bio and 1.0 for photodegraded specimens, representative of semi-entangled systems. The temperature coefficient of the growth rate, analyzed according to secondary nucleation leads to a linear dependence for bio and photodegraded specimens, and to values of the surface free energy of crystallites that decrease from ∼85 to 55 erg/cm2 with decreasing molar mass. Combinations of molar mass characterization, FTIR, and thermal and crystallization rate analysis are proven useful strategies to assess and discriminate macroscopic changes of PLA structure induced by different types of degradation. This work also underlines the importance of analyzing the linear growth rates as a parameter that uncovers specific structural changes during degradation.

The influence of the industrial processing on the degradation of poly(hidroxybutyrate) - PHB

PHB was characterized after different industrial processes by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Melt Flow Index (MFI), Complex Dielectric Relaxation (CDR) and Size Exclusion Chromatography (SEC). Some properties of PHB were investigated before and after processing, in order to understand how temperature and other extrusion or injection conditions affect the polymer degradation. All the processed samples showed an increasing in the melt flow index, a decreasing of the dynamic crystallization temperature, and a reduction in the molar mass, suggesting some degradation. The molar mass reduction after processing, predicted when only thermal degradation is considered, was calculated in function of the kinetic parameters, such as constant thermal degradation and residence time during the industrial processing. It was found that the real molar mass reduction was higher than the theoretical value, indicating an important contribution of the shearing of polymeric chains during processing in the PHB degradation.

Thiomers: Influence of molar mass on in situ gelling properties

The aim of this study was to investigate the influence of molar mass of thiolated polymers (thiomers) on their in situ gelling properties. Chitosan-thioglycolic acid (chitosan-TGA) and pectin-cysteine (pectin-Cys) of increasing molar mass were chosen to produce in situ gels in combination with carbamide peroxide. Low molar mass chitosan (~2 kDa) was prepared by oxidative degradation with NaNO(2), whereas pectin was depolymerized by heat treatment. Thiomers, displaying 1271-1616 μmol (chitosan-TGA) and 305-403 μmol (pectin-Cys) free thiol groups per gram polymer, were synthesized via amide bond formation mediated by a carbodiimide. The results showed that a reduction of molar mass combined with increased concentrations of both cationic chitosan-TGA and anionic pectin-Cys leads to higher final viscosities and to a higher relative increase in viscosity within 60 min and 180 min, respectively. Using this method, the dynamic viscosity of a very low molar mass chitosan-TGA (~2 kDa) could be increased 100,000-fold within 60 min and 390,000-fold within 180 min. In view of these in situ gelling properties carbohydrate thiomers might be useful for various pharmaceutical applications such as vehicle for drug delivery or as wound dressing material.

Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechanical performance

This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystallization during DSC and DMTA measurements, which enthalpy increased with each reprocessing step, suggested chain scission due to thermo-mechanical degradation. The effect of chain shortening on the glass-rubber relaxation studied by DMTA showed an increase in free volume affecting the segmental dynamics of PLA, particularly after the application of the second reprocessing step, in connection to the overall loss of performance showed by the remaining properties.

Production and characterization of poly(3-hydroxybutyrateco-3-hydroxyhexanoate)-poly(ethylene glycol) hybird copolymer with adjustable molecular weight

A novel natural-synthetic hybrid block copolymer was synthesized by Aeromonas hydrophila 4AK4 in poly(ethylene glycol) (PEG, Mn = 200) modified fermentation. This hybrid biomaterial consists of the natural hydrophobic polymer poly(3-hydroxybutyrat-co-3-hydroxyhexanoate) (PHBHHx) end-capped with hydrophilic PEG, which has the increased flexibility as well as the improved thermal stability. Addition of diethylene glycol (DEG) and ethylene glycol could not result in the accumulation of hybrid block copolymer. DEG and ethylene glycol, together with PEG-200, could cause a reduction of molar mass of PHBHHx, resulting in a series of low molecular weight polymer and the reduction of the polymer yield as well as the cellular productivity. In vitro degradation of PHBHHx and PHBHHx-PEG with different molecular weight showed that the decrease of molecular weight accelerated the degradation of copolymers, but PEG modification has little effect on its degradation rate. The results in this study provided a convenient and direct method to produce a series of PHBHHx and PHBHHx-PEG materials with adjustable molecular weight and broad molecular weight distribution which will be very useful for the biomedical applications.

The role of crystalline, mobile amorphous and rigid amorphous fractions in the performance of recycled poly (ethylene terephthalate) (PET)

The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation of –OH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percentage of crystalline fraction remained nearly constant. A deeper analysis of the melting behaviour, the segmental dynamics around the glass-rubber relaxation, and the macroscopic mechanical performance, showed the role of each fraction leading to a loss of thermal, viscoelastic and mechanical features, particularly remarkable after the first processing cycle.

Synthesis and polymerization reactions of cyclic imino ethers. 5: naphthalene unit-containing poly(ether amide)s

Poly(ether amide)s containing naphthalene unit were prepared either by the polyaddition reaction of aromatic bis(2-oxazoline)s with the different dihydroxynaphthalenes or by the homopolyaddition of a monomer containing an oxazoline, a hydroxy, and naphthalene moieties. First, polymerization method represents AA + BB mode where 1,4-phenylene-2,2′-bis(2-oxazoline) (A) and 1,3-phenylene-2,2′-bis(2-oxazoline) (B) were used as AA monomers and four different dihydroxynaphthalenes 1–4 were used as BB monomers. In the second case, 2-(6-hydroxynaphthalene-2-yl)-2-oxazoline (5) was used as AB-type monomer in thermally induced polymerizations. The time dependences of polyadditions in bulk as well as in the solution were examined. The reduction of molar mass was observed after the initial fast increase of molar mass. This can be explained by the presence of side and degradation reactions. In both cases, polyadditions resulted in the linear poly(ether amide)s, which were characterized by 1H and 13C NMR spectroscopy. Thermal properties of the prepared polymers were studied by differential scanning calorimetry (DSC) measurements. Comparison of the temperatures of glass transition for polymers prepared in AA + BB mode shows the strong dependence of thermal properties on the structure of the polymers. The values were in the range of 136–171°C. The glass-transition temperature (Tg) of poly[2-(6-hydroxynaphthalene-2-yl)-2-oxazoline] prepared by AB-type polyaddition is 183°C, which corresponds to the higher contents of hard aromatic segments in the latter type of polymers compared to the polymers prepared in the AA + BB-type polyadditions. The described polymers represent novel naphthalene unit-containing poly(ether amide)s for different applications in material science. Copyright © 2011 John Wiley & Sons, Ltd.

Synthesis of Polyurethane from Poly(3‐hydroxybutyrate) and Poly(p‐dioxanone): Molar Mass Reduction via Sodium Borohydrate

AbstractPoly(3‐hydroxybutyrate) PHB and poly(p‐dioxanone) PPD are examples of promising polymers in tissue engineering. The purpose of this work is to synthesize polyurethanes which combine stereoregular and rigid blocks of PHB with stereoregular and flexible blocks of PPD. In order to guarantee stereoregularity, polyols from PHB and PPD were obtained from mass reduction via sodium borohydrate. This route allows us to obtain bifuncional polyols. The polymer molar mass reduction using this strategy was effective, however secondary and non reactive products with diisocyanate like insaturated acid were formed as shown by mass spectroscopy data. The products of mass reduction were characterized by H1 NMR, FT‐IR, DSC and MALDI‐TOF/MS. The PU's were synthesized reacting the polyols with hexamethylene diisocyanate (HDI) and they were characterized by FT‐IR, H1 NMR, DSC and XRD.The PU obtained from PHB and PPD polyols presents two crystalline phases, corresponding to both polyester blocks. The introduction of flexible segments of PPD in polyurethane, affected the characteristics of crystalline phase formation of PHB, increasing the melting point of this block in comparison with the pure PHB polyol, probably by increasing the crystallization rate.

Study on In-Vitro Degradation of Bioabsorbable Polymers Poly (hydroxybutyrate-co-valerate) - (PHBV) and Poly (caprolactone) - (PCL)

The increasing use of bioabsorbable polymeric materials in medicine has stimulated researchers in the materials field to search for solutions for the replacement of metallic artifacts by bioabsorbable polymers. Therefore, this study describes the in vitro degradation of PHBV, PCL and the blends of these polymers, both of which are bioabsorbable polymers. The samples were prepared by extrusion followed by injection, and subjected submitted to in vitro degradation in phosphate buffered saline solution with pH 7.3 and kept at 37° C. Through the characterization of the variation of mass, molar mass, mechanical properties and morphology, the results indicated that the samples analyzed are more stable to hydrolytic degradation when compared to other bioabsorbable polymers. The materials indicate signs of degradation after 30 days, with a small reduction in the molar mass. After 180 days, the materials indicated a significant reduction of molar mass and reduction in the mechanical properties.

Degradability of linear polyolefins under natural weathering

High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here.

Hydrolytic stability of polybenzobisoxazole and polyterephthalamide body armor

Previous work conducted at the National Institute of Standards and Technology (NIST) to investigate the field failures of soft body armor containing the material poly( p -phenylene-2,6-benzobisoxazole), or PBO, revealed that this material was susceptible to hydrolysis, and a mechanism of this hydrolysis was proposed. In this work, viscometric estimations of the molar mass of environmentally conditioned PBO are used to support a previously proposed mechanism of PBO hydrolysis. Results with PBO were compared with poly( p-phenylene terephthalamide), or PPTA, which has been used in body armor applications for more than 30 years. Losses in tensile strength were found to correspond to a reduction in molar mass for PBO. This indicates that chain scission due to complete hydrolysis is occurring in this material. Similar trends were observed for PPTA, but the relationship between molar mass reduction and losses in tensile strength was not as evident for this material. Confocal microscopy, mechanical properties measurements, and molecular spectroscopy are used to further investigate the degradation of both PBO and PPTA.

Particulate structure of phytoglycogen nanoparticles probed using amyloglucosidase

Phytoglycogen is a plant-based, high-density carbohydrate nanoparticle that can be used as a starting material for preparing novel functional nano-constructs. In this study, the particulate structure of phytoglycogen was probed using amyloglucosidase hydrolysis, with amylopectin of waxy corn starch as a reference. Glucose release was monitored; molar mass, root mean square (RMS) radius, and dispersed molecular density were evaluated using multiangle laser-light scattering. The goal was to reveal the structural features of phytoglycogen nanoparticles. After extended amyloglucosidase hydrolysis, the total glucose release of phytoglycogen was lower than that of amylopectin. At the initial stage of hydrolysis, however, glucose was released at a higher rate from phytoglycogen, suggesting a dense distribution of nonreducing ends at the surfaces of nanoparticles. The reduction of molar mass and RMS radius caused by amyloglucosidase hydrolysis were much lower for phytoglycogen than for amylopectin. The dispersed molecular density of amylopectin remained at about 60 g/mol nm 3 during hydrolysis. In contrast, the density of phytoglycogen decreased from about 1200 to 950 g/mol nm 3, suggesting a density increment towards the external region of nanoparticle.

Stress cracking and chemical degradation of poly(ethylene terephthalate) in NaOH aqueous solutions

AbstractStress cracking is one of the most frequent causes of premature failure of polymers, affecting also engineering polymers like PET. In this work, the stress cracking behavior of injection moulded PET was investigated using sodium hydroxide (NaOH) aqueous solutions in various concentrations as active fluids. The application of mechanical load to the sample bars was done in a tensile testing machine, using the ordinary tensile test and also a relaxation procedure. The results showed that all NaOH solutions were aggressive stress cracking agents for PET, reducing mechanical properties and causing catastrophic failure with a significant surface damage. The occurrence of hydrolysis reactions was also observed when NaOH solutions were applied in combination with tensile loads, causing a reduction in molar mass of PET molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010