When Are the Mechanical Rates Due to Change Again

Properties

Michael Niaounakis , in Biopolymers: Processing and Products, 2015

ii.3.seven.1.3 Mechanical Degradation

Biopolymer articles can undergo several mechanical degradations during processing, storage and use. Mechanical degradation can take place due to shear forces, tension, and/or compression [49,fifty]. Agitation, grinding, or extrusion are the main causes of mechanical deposition during processing. The basic phenomenon involved when subjecting the polymer to very powerful shearing forces is the breakage of the molecule. Mechanical degradation reduces the boilerplate molecular weight of the polymer.

Although mechanical factors are not predominant during biodegradation, they can activate or advance it. In field conditions, mechanical stresses human action in synergy with the other environmental parameters such every bit temperature, UV, humidity, etc. [39].

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Polymers for a Sustainable Environment and Green Energy

D.A. Schiraldi , D. Savant , in Polymer Science: A Comprehensive Reference, 2012

10.38.ii Mechanical Degradation of Polymer Electrolyte Membranes

Mechanical degradation of PEMs can come in the form of perforation, cracks, tears, and pinholes and may effect from manufacturing defects in the membrane moving picture, from damage inflicted upon the membrane during assembly, or from cycling of humidity, temperature, and/or electrical potential of the fuel cell. ¹⁹ Particularly vulnerable are the areas of the membrane side by side to country/channel interfaces in the fuel flow field and the sealing edges of the fuel cell. The most commonly discussed cause of impairment due to cycling results from humidity changes which can rapidly change from dehydrated to flooded; ^xx–22 changes in mechanical size upshot from these humidity swings, bringing almost mechanical stresses upon the membrane. ^22–24 For a membrane physically constrained within a membrane electrode assembly, in-plane tension on the polymeric film results from such humidity cycling. Physical debris which results from corrosion of metallic parts of the fuel cell assembly and from catalyst degradation can lodge in the polymeric membrane, serving then as a physical stress concentrator, which can hasten the failure of the membrane; ¹² addition of a microporous membrane layer capable of catching such debris has been shown to exist constructive under some atmospheric condition, at lengthening FC operating lifetimes. ²⁵ The effects of cold starts (below the freezing bespeak of h2o) upon the physical state of PEM assemblies accept varied from none observed ²⁶ to significant damage. ²⁷ Mechanical cycling of Nafion® membranes through nearly 400   freeze/thaw cycles (–twoscore to 80   °C) was found to have little event on the polymer limerick, along with a 30% loss in tensile strength, significant loss in ductility, yet lilliputian change in water absorbency. Such changes tin can be attributed to physical reorganization of the membrane polymer (eastward.yard., changes in polymer chain entanglements), rather than degradation of that material, and did not constitute a catastrophic effect. ^fifteen Physical damage is not express to the membrane itself, just can besides pertain to neat of the catalyst layer practical to the membrane or delamination of the catalyst layer from the membrane. ^13,28 These physical effects can be mitigated by purging with dry gases, presumably removing excess h2o, and therefore minimizing ice germination and physical expansion/applied stress to the polymer. ¹⁶ Such vagaries of experimental methods utilized past dissimilar authors make it extremely difficult to compare bodies of work in a meaningful mode; the studies ofttimes demonstrate that a failure way is possible without conspicuously demonstrating that the mode is 1 likely to be available within an actual, operating fuel cell. It is possible to accurately measure properties associated with the unlike modes of cycling (stress and strain at break and Young'southward modulus), allowing for predictions of membrane mechanical stability for standard membranes, equally well as for reinforced systems; ^fifteen care needs to exist taken in modeling the actual operating conditions that the fuel cell is likely to feel during its useful life. The stress–strain beliefs of Nafion® has to be measured as a function of hydration, equally water serves equally a plasticizer which therefore decreases modulus and tensile force, while increasing the ductility of the polymer. ²⁹ The moduli for the ionomers in their proton, lithium, and sodium forms are known to exist similar, but those ion exchanged with potassium, rubidium, and cesium exhibit twice that value in the 25–80   °C operating temperature range, and even higher at elevated temperatures. Hence, in add-on to deposition of PEMFC polymer materials, changes in equilibrium physical structure of the polymer, 1 has to exist concerned with migration of goad and corrosion metals and their furnishings on the mechanical resistance of membranes during fuel cell functioning. ¹⁶ A difficulty in evaluating either mechanical or chemical degradation of PEM systems is the long times for which the membranes are expected to operate. In order to evaluate the performance of the PEMFC over 40   000   h, an experiment of 4.5 years is required. Accelerated lifetime tests, using more farthermost operating atmospheric condition, or radical changes in operating conditions at a rate far more frequent than would actually occur are most often utilized in durability studies. In whatsoever such test authorities, information technology is important to critically challenge the method past which the concrete (or chemical) insult is applied to the PEMFC. It is possible to create a organisation so aggressive, for instance, that while deposition is indeed accelerated, physical modes of activeness or chemical pathways not generally bachelor inside a normally operating fuel cell are operating, providing lifetime failure data that are non representative of those available inside operating fuel cells. Despite these concerns about ultimate validity of experimental exam protocols, pattern features which distribute stresses resulting from procedure cycling across the widest part of the membrane possible would appear to be a good practice, equally is great intendance in membrane product to minimize any physical defects inherent in the membrane.

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Recycling of Polylactide

José D. Badia , ... Amparo Ribes-Greus , in Encyclopedia of Renewable and Sustainable Materials, 2020

Deposition Mechanisms of PLA Induced past Mechanical Recycling

Thermo-mechanical degradation induced by mechanical recycling of PLA considers the impact of deposition agents such equally temperature, oxygen, humidity, mechanical stresses, or calorie-free, individually or in combination. Even if technical measures are taken to prevent the contact of PLA with the environment at high temperatures, oxidation, and hydrolysis stop upward in concatenation scission reactions; while transesterifications alter the tooth mass distributions of the polymers and therefore bear upon to their morphological properties in terms of amorphous-to-crystalline ratio, chirality, or steric rearrangements. The temperature of many PLA processing routes should non exceed 230°C to avoid thermal degradation via nonradical reactions, which would pb to a significant decrease in molar mass that has an important effect on the performance of PLA.

A particular assay of the macromolecular species that take place during mechanical recycling of PLA was carried out by Badía et al. (2011). The postulated mechanistic routes, as obtained from MALDI-TOF-MS analysis, along with the evolution of oligomeric species encountered after upwardly to five injection–grinding cycles is shown in Fig. 2. The principal reactions are hydrolysis (route I), which provoke the formation of hydroxyl and carboxyl linear oligomers with shorter chain length. In addition, esterification and intra- and intertransesterifications (routes II, III, and IV, respectively) occur by backbiting, that is, from the end of the chain, and at the eye of the chain, which leads to the formation of cyclic oligomers and linear species with shorter length, modifying the molar mass distribution. The most remarkable changes were those occurring for linear H-[LA_Fifty]_northward-O-CH₃ species, which presented a noticeable increment, beingness the most predominant species after iii processing cycles, and achieving a proportion of upward to twoscore% for the fourth recyclate.

Fig. 2. Deposition pathways (up) and evolution of oligomers (downward) as a result of the application of 5 successive thermo-mechanical cycles. Legends: square: [LA_C]_n; circumvolve: CH₃-O-[LA_L]_n-H; upwards-triangle; HO-[LA_L]_n-H; down-triangle: CH₃-O-[LA_L]_n-CH_three; diamond: CH₃-CO-O-[LA_L]_{due north}-CH₃, where LA stands for lactic acid repeating unit, L stands for linear and C for cycling oligomeric species.

Reproduced from Badía, J.D., Strömberg, E., Amparo, R.G., Karlsson, Due south., 2011. Assessing the MALDI-TOF MS sample preparation procedure to analyze the influence of thermo-oxidative ageing and thermo-mechanical degradation on poly (Lactide). European Polymer Periodical 47 (7), 1416–1428. doi:10.1016/j.eurpolymj.2011.05.001.

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Polymer Reactions

Junkichi Sohma , in Comprehensive Polymer Science and Supplements, 1989

23.three Main Chain Scissions Induced by Mechanical Forces

Earlier discovery of mechanical degradations of polymers, which was done by safety engineers, was based on the observed decreases in molecular weight after mechanical processing. The majority of the mechanoradicals which are listed in Table i and 2 are of the concatenation-scissioned blazon. Combining these facts one might immediately conclude that the primary reaction induced by mechanical forces is master concatenation scission of polymers. This conclusion seems quite plausible but does not give a unique explanation of the arrangement considering β scission ³⁴ of a chain radical ( 4 ) results in formation of a chain-scissioned radical and β scissions are commonly constitute in polymers. ³⁴ In such a case chain breaking is a secondary reaction of the concatenation radical. Thus, the presence of a chain-scissioned radical is not sufficient evidence that polymer chains are primarily broken by the effect of a mechanical force. In order to verify a principal chain scission of a polymer every bit a primary reaction induced by a mechanical strength, one has to testify formation of a pair of radicals (5) and (half dozen) from a polymer ( 7 ). Ane cannot bear witness pair formation of radicals for the simplest polymers such as PE or poly(tetrafluoroethylene) because a radical species produced by main chain scission is identical with a species produced by β scission.

The ESR spectrum observed from polypropylene (PP) milled by the ball-manufacturing plant apparatus shown in Figure 1 is shown in Figure 6(a). The spectrum in Figure half-dozen(b) is a simulation spectrum derived from a superposition with a one to 1 relative ratio of the two radicals, (8) and (nine). Agreement betwixt the observed spectrum and the false one is satisfactory. Thus, one can conclude that pair formations of the ii radical species is induced by ball-milling in vacuum at 77   Thou. ^35,36 This result is positive evidence for chain breaking of PP as the primary reaction.

Figure half dozen. ESR spectrum observed at 77   G from PP milled at 77   K; (b) simulated spectrum on the basis of the radical pair formed by primary-chain scission

ESR spectra observed at 77   Thousand from ball-milled poly(methyl methacrylate) ³⁷ in vacuum are shown in Figure 7. The line-shapes are different, depending on the milling time. The spectrum observed after long milling of 18 hours (Figure 7c) is decomposed into two components, a nonent and a doublet, equally shown in Figure vii(c). The nonet is the characteristic spectrum of the PMMA radical ( three ). ³⁸ The doublet is assigned to a radical ( 10 ). Based on the decomposition of the spectrum in Figure seven(c) into two components, 1 more component, a triplet, is discoverd in the spectrum shown in Figure 8(a), i.e. the spectrum decomposes into 3 components, a nonet, a doublet and a triplet. The triplet is attributed to the radical species ( ii ). The relative intensity of the nonet is approximately equal to the sum of the intensities of the triplet and the doublet. The radical responsible for the triplet is a partner radical to ( 3 ), which gives the nonet, suggesting that these are formed by main chain scission. The radical for the doublet is generated past hydrogen abstraction of the radical ( ii ) from the PMMA molecule. This ways the radical producing the triplet is the precursor of the radical producing the doublet. The equality of the sum intensity of these components, the triplet and the doublet, to that of the nonet suggests that the radical producing the triplet is the partner of the radical producing the nonet in the pair formation. In the instance of PMMA the pair formation is proved in a more complicated way than for PP, but germination of radicals (2) and (3) is regarded equally positive evidence for principal chain scissions beingness induced primarily by the milling of PMMA.

Figure vii. ESR spectra observed at 77   K from PMMA milled at 77   M. After milling for (a) 0.one   h, (b) 5.0   h and (c) eighteen.0   h. In spectrum (c) the bold line represents the observed spectrum, the thin line represents the nonet and the dotted line the doublet

Figure 8. Decomposition of the observed spectrum in Figure 7(a): the thin line represents the observed spectrum, the dotted line represents the nonet and the assuming line represents the superposition of the triplet and the doublet

PP and PMMA are the merely examples for which pairs of radicals produced by main chain scissions accept been positively proved. Information technology is rather hard to prove pair formation fifty-fifty if the principal chains are cleaved by mechanical action because partner radicals in pair germination have dissimilar reactivities in subsequent reactions, as demonstrated in the case of PMMA. Therefore, it is not easy to obtain positive and exact show for formation of pairs of radicals having equal relative concentrations.

The situation in a liquid phase is a little more than complicated than that in the solid country. The ESR spectrum from a PMMA–benzene solution was observed using the spin-trapping technique. The best simulated spectrum is based on the equal relative intensities of two components of the triplet and the triple triplet. The radicals responsible for these components are the partner radicals generated past a main chain scission of the PMMA molecule. The equal intensities of the two components strongly advise pair germination of these radicals. However, the spectral components are not from the radicals themselves but from the spin adducts of the radicals. The trapping rates for two different kinds of radical are possibly different and therefore the concentrations of the spin adducts are not exactly proportional to the radical concentrations in the case of unlike rates. Strictly speaking, equal concentrations of the spin adducts do non necessarily imply equal concentrations of the original radicals. It is known, ³⁹ however, that trapping rates of similar chemical species are similar and the equal concentrations of the spin adducts can safely be interpreted equally being those for the original radicals, to a good approximation at to the lowest degree. Therefore, the experimental result obtained for the PMMA–benzene solution is considered to be evidence for a main chain scission of the PMMA molecule, induced either by ultrasonic irradiation or by high speed stirring.

Although exact and positive evidence for primary concatenation scissions induced primarily by mechanical forces has not been obtained for most polymers, germination of chief radicals of the chain-scissioned blazon, which are listed in both Table ane and Tabular array 2, could be considered as experimental evidence supporting the mechanically induced main chain scissions, which are analogous reactions to those proved for both PP and PMMA either in the solid phase or in the liquid stage. Therefore, it seems reasonable to presume that the chief reactions induced by mechanical forces applied to polymers are main concatenation scissions on the basis of both the detected species of mechanoradicals and the considerations described above.

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Durability testing and evaluation of marine composites

Oliver Parks , Paul Harper , in Marine Composites, 2019

4.5.one Testing methodology

In club to investigate the mechanical degradation of blended laminates in a chosen workout medium, specimens are tested to failure after workout and compared against identical, nonconditioned dry specimens.

The extent of testing required is dependent on the purpose of the tests and use of the data. To compare the wet degradation of different laminates for the purpose of material option, it is generally considered acceptable to investigate simply ii mechanical backdrop;

Interlaminar shear stress (ILSS): This value is highly dependent on resin properties. It is a good indication of resin and resin/fiber interface forcefulness, and hence, resin degradation when comparison dry and conditioned results. At that place are multiple examination methods available for obtaining this property, the simplest being the three-betoken curve short beam shear exam. The simplicity of coupon geometry and test procedure is peculiarly advantageous when conducting a big number of tests in an industrial environs. ASTM D2334 and ISO 14130 provide detailed accounts of the testing procedure. Other tests are available such as double-notched shear; however, coupon preparation is more complex. A Double Axle Shear (DBS) test using 5-point loading has been the subject field of an international ISO round-robin.

Flexural strength: This property is an indication of fiber and fiber/matrix interface strength, as well equally cobweb and sizing degradation. ASTM D7264 and ISO 14125 both define procedures for obtaining this value from three- and iv-signal bending tests. Once more, the examination coupons are quite simple and therefore preferred for comparative investigations.

These 2 properties give a quick and fairly reliable indication of general laminate performance and permit for a quick comparison between unlike laminates and materials. Information technology is important to understand the assumptions and limitations of both tests, even when following the test standards. The combination of specimen geometry and elective properties volition determine the proportion of directional loading within the specimen, which determines the failure style; an essential consideration.

For detailed structural design, more than extensive testing is required. Generally, this will entail static and fatigue testing of various coupons and load conditions; including tension, compression, and in-plane and interlaminar shear. Larger specimens tin be tested separately with intentional defects such every bit holes and ply drops to be more representative of real-world structures. These tests are ofttimes conducted on dry specimens equally thicker coupons tin take significantly longer to saturate. The separate furnishings of local defects and moisture degradation are normally combined during product design. Designs incorporating thick monolithic laminates may also crave knowledge of out-of-airplane backdrop.

The test pyramid describes a standard arroyo used in many industrial design projects. Fig. 4.2 displays a examination pyramid for a typical loftier-performance marine structure. A larger number of more affordable ply and laminate-level tests support fewer large scale structural tests. The entire structural design may exist validated with a total scale paradigm. The goal of a test pyramid is to assistance the designer reach a suitable compromise between cost and structural validation. For instance, the certification standard for tidal and wave energy converters (DNV, 2008) suggests supporting analytical design with cloth and prototype testing, amid others.

Fig. 4.two. Typical testing pyramid for high-performance marine structures.

A greater agreement of the physical processes by which materials degrade over time in a marine environment will enable designers to supersede a pregnant portion of the lengthy, costly examination programs with faster, cheaper simulations and numerical predictions. Numerical models are beingness developed; however, they are at early stages and require extensive test data for validation. It has been suggested that, to help accelerate this procedure, as well as improve the applicability of such models for both academic and industrial purposes, a express number of resin, sizing, and cobweb combinations should exist selected for investigation and commercial use.

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Lightning strike damage on carbon fiber-reinforced composites: Prediction and protection

Huixin Zhu , ... Bin Yang , in Composite Materials, 2021

14.iii.2.one Basic theory

Ablation or mechanical damage induces the mechanical degradation of CFRCs. The constitutive equation of a CFRC with harm can exist expressed equally [24]

(14.9) $\left\{\sigma \right\}=C^d\left\{\varepsilon \right\}$

where {σ}is the stress vector and {ɛ} is the strain vector. C ^d is the stiffness matrix of the damaged CFRC, which is defined equally

(xiv.10) $C^d=\left[\begin{array}{llllll}\left(\mathrm{i}-d_{\mathrm{one}}\right)C_{11}& \left(1-d_1\right)\left(1-d_2\right)C_{12}& \left(\mathrm{ane}-d_1\right)\left(\mathrm{one}-d_{\mathrm{three}}\right)C_{\mathrm{xiii}}& & & \\ \left(1-d_2\right)\left(1-d_1\right)C_{21}& \left(\mathrm{ane}-d_2\right)C_{22}\hfill & \left(1-d_2\right)\left(\mathrm{ane}-d_3\right)C_{23}& & & \\ \left(1-d_{\mathrm{three}}\right)\left(1-d_{\mathrm{ane}}\right)C_{31}& \left(1-d_{\mathrm{three}}\right)\left(\mathrm{one}-d_2\right)C_{32}& \left(\mathrm{i}-d_{\mathrm{iii}}\right)C_{33}\hfill & & & \\ & & & \left(\mathrm{one}-d_1\right)\left(1-d_2\right)C_{44}& & \\ & & & & \left(1-d_1\right)\left(\mathrm{one}-d_{\mathrm{three}}\right)C_{55}& \\ & & & & & \left(\mathrm{ane}-d_2\right)\left(\mathrm{i}-d_{\mathrm{three}}\right)C_{66}\end{array}\right]$

where d represents damage variables and C represents elastic constants. Every bit already mentioned, mechanical constraints include magnetic pressure level, and pyrolysis gas explosions, etc. The respective equations of the mechanical loading acquired past a lightning strike are listed beneath.

The effective magnetic pressure caused past a lightning strike is expressed as [25]

(14.xi) $P\left(r,t\right)=\frac{{\mu }_{0}I{\left(t\right)}^{\mathrm{two}}}{\mathrm{eight}{\pi }^{\mathrm{two}}r{\left(t\right)}^{\mathrm{ii}}}$

where μ ₀ is the permeability of the free space. r(t) is the arc root radius. The value of the magnetic force per unit area is insignificant compared to the other mechanical constraints.

The pressure impulse caused past high-temperature plasma expansion tin can be determined. The distance of plasma expansion Fifty(t) in a fully protected CFRC is given by [21]

(xiv.12) $\frac{{\mathit{d}}^2\mathrm{Fifty}\left(t\right)}{{\mathit{dt}}^{\mathrm{two}}}=\left(\frac{1}{{\mu }_p}+\frac{1}{{\mu }_c}\right)P\left(t\right)$

where μ _p and μ _c are the mass per unit area of the LSP layer and the CFRC. P(t) is the pressure impulse. The ability is adamant as

(14.13) $\mathrm{Q}\left(t\right)=P\left(t\right)\frac{\mathit{dL}\left(t\right)}{\mathit{dt}}+\frac{d}{\mathit{dt}}\left(\frac{\mathrm{iii}}{2F}P\left(t\right)\mathrm{50}\left(t\right)\right)$

where F is the energy conversion rate, defined as the fraction of the kinetic energy of the plasma to the total energy. Q(t) can exist simplified every bit

(xiv.14) $\mathrm{Q}\left(\mathrm{t}\right)\approx \frac{5_{\mathit{eq}}I\left(t\right)}{\mathit{\pi r}{\left(t\right)}^2}$

where V _eq is the potential on the surface. Thus, the plasma expansion-induced pressure level impulse P(t) can be determined using Eqs. (13) and (14).

Liu et al. [8] presented a blow-off impulse model using a modified PUFF equation. The blow-off impulse is expressed as

(xiv.15) $P\left(\mathrm{V},\mathrm{East}\right)=\mathit{H}\left[A\left(\mathrm{one}-\frac{\omega }{R_1\mathrm{Five}}\right){\mathrm{eastward}}^{-R_{1}V}+B\left(\mathrm{one}-\frac{\omega }{R_{2}5}\right)e^{-R_{2}V}+\frac{\mathit{\omega E}}{V}\right]$

where V is the book. E is the internal free energy density of the initial book. A, B, R _ane, R ₂, ω are the material constants. H is given by

(xiv.16) $H=max\left(H_{\mathrm{ane}},H_2\right)$

in which H ₁ and H ₂ are expressed as

(14.17) $H_1=\left\{\begin{array}{cc}\frac{\mathrm{ii}\left(t-t_1\right){\mathit{DA}}_{\mathrm{eastward}max}}{\mathrm{iii}{\mathrm{Five}}_e},& t>t_{\mathrm{i}}\\ \mathit{0},& t\le t_{\mathrm{i}}\end{array}\right.$

(14.18) $H_2=\frac{\mathrm{i}-V}{\mathrm{ane}-5_{\mathit{CJ}}}$

where t is the current time and t _ane is the lightning time. D is the detonation velocity. A _emax is the maximum surface area of an element and 5 _e is the volume of the chemical element. Five _CJ is the Chapman Jouguet relative volume.

Lee et al. [10] developed an overpressure model of lightning strike, in which the overpressures practical on the CFRCs were the combination of the incident overpressure P _io and the reflected overpressure P _ro given past

(xiv.19) $\mathrm{P}\left(\mathrm{t}\right)=\left\{\begin{array}{l}{P}_{\mathit{io}}\left(t\right)\left[1+cos\theta -2cos{\theta }^2\right]+P_{\mathit{ro}}\left(t\right)cos{\theta }^2,cos\theta \ge 0\\ P_{\mathit{io}}\left(t\right),cos\theta <0\end{array}\right.$

where θ is the oblique angle.

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FUEL CELLS – PROTON-EXCHANGE MEMBRANE FUEL CELLS | Membranes: Design and Characterization

S.M. MacKinnon , ... A.M. Brenner , in Encyclopedia of Electrochemical Power Sources, 2009

Accelerated chemical and mechanical durability

Through the introduction of a chemical stressor into the accelerated mechanical deposition test, we accept developed a demanding accelerated examination to evaluate membranes that includes both main stressors that a membrane experiences during fuel cell performance. Membranes are evaluated in this test using l cm ^two-active surface area-MEAs prepared with CCDMs containing 0.4   mg Pt cm⁻² on both the anode and the cathode. Membranes are subjected to RH cycling with reactive gases (hydrogen and air) at a constant electric current density of 0.ane   A   cm⁻², as shown in Figure 6. In these tests, hydrogen air stoichiometry is 20 on both the anode and the cathode to enable near uniform RH throughout the cell. The RH bicycle is the same as the accelerated mechanical durability exam with a 2 min, 0%-RH hydrogen and air flow followed by a 2 min, 150%-RH hydrogen and air flow, at lxxx   °C and 0   kPa_g back pressure. The added chemical degradation significantly accelerates the fourth dimension to ten   mL   min⁻¹ crossover leak for both the homogeneous 25-μm Nafion membranes and the reinforced Gore™ Primea® MEAs, as shown in Table three. The observed number of RH cycles to decide failure is reduced past at least a factor of v relative to the inert humidity cycling tests without an electric load. Furthermore, the extruded N111-IP membrane from Ion Power, which passed the accelerated mechanical durability exam after 20   000 cycles, develops a crossover leak after but 1800 humidity cycles at 0.one   A   cm⁻². Clearly, chemical degradation causes mechanical weakening of these PFSA membranes.

Effigy 6. Accelerated chemical and mechanical durability protocol.

Table 3. Comparison of relative humidity (RH) cycling with inert gases and at 0.1   A cm⁻²

Membrane	Accelerated mechanical immovability (# of cycles)	Accelerated chemic–mechanical durability (# of cycles)
DuPont™ Nafion® (NRE-211)	4500	800
Ion Power™ Nafion® (N111-IP)	20000	1800
Gore™ Primea®	6000–7000	1300

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In Vitro Characterization of Cell–Biomaterials Interactions

Y.M. Thasneem , Chandra P. Sharma , in Characterization of Biomaterials, 2013

5.1.3.7 Constructed vs. Naturally-Derived Polymers

The processing dexterity of constructed polymers in terms of composition, rate of deposition, mechanical, and chemical properties keep us confused in front of the compositional uniqueness, such every bit stimulating a specific cellular response provided by the naturally derived polymers. Of the numerous synthetic polymers, a few accept been examined in more detail: poly (North-isopropylacrylamide), PEG, and PLGA driven by its interesting thermal and non-cell adhesive properties [34]. Agraose, hyaluronan, collagen, and fibrin possess the virtually compelling depression poly peptide-adsorbtive and jail cell-adhesive properties among the naturally derived polymers. Being the biochemical players inside the body, these polymers possess recognizable receptors like CD44 for hyaluronan easing its manipulation for multiple platform applied science similar wound healers [35].

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Synthesis and Application every bit Programmable H2o Soluble Adhesive of Polyacrylamide Grafted Gum Tragacanth (GT-g-PAM)

Pinki Pal , ... Gautam Sen , in Biopolymer Grafting, 2018

i.8.half dozen Freezing and Thawing Method

During the freezing and thawing of polymers in aqueous medium, stresses are developed that result in the mechanical degradation of the macromolecular chains. The transformation of water into ice is connected with an increase in volume and the evolution of mechanical stress, which may exceed the strength of covalent bonds. In the process of thawing polymers, which has been previously swollen in water, the h2o initially penetrates into the amorphous region where concatenation packings are loose. This would likewise be expected to create internal stresses, resulting in the breaking of polymer chains ( Ceresa, 1962).

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Degradation of Polymer Matrix Composites☆

Rodney H. Martin , Doc. Sayem H. Bhuiyan , in Reference Module in Materials Science and Materials Engineering, 2018

2.6 Mechanical Degradation

This article focuses more than on the ageing of FRPs nether environmental loads, and, strictly speaking, mechanical deposition is non part of ageing. Nevertheless, information technology is oftentimes a consequence of ageing. Mechanical damage processes such as matrix cracking, delamination, plastic strain, interfacial failure are generally irreversible. In an FRP, some of these damage modes may be seen to exist benign or subcritical; however, the damage may accumulate or lead to harm elsewhere past transferring load ultimately leading to failure. The well-nigh common mechanical deposition, especially when operating at loftier temperature, is the formation of cracks in the matrix either within the ply or transverse to the ply. Fatigue, environmental loading, and residual stresses can all promote the onset and accumulation of these cracks. The laminate strength, stiffness, and thermal properties as well as failure modes tin can be afflicted by transverse matrix keen which can also promote college uptake of moisture deeper in the laminate. The prediction of these failure modes are often parts of a long-term durability assessment, especially nether fatigue loads. The reader is directed towards Jones, ^ane Mathews and Rawlings, ⁴ and ASM Handbook, ⁵ for a description of predicting mechanical failure in FRP laminates.

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