Introduction

Casale, Antonio; Porter, Roger S.

doi:10.1016/b978-0-12-162801-7.50008-2

Cited by 17 publications

(12 citation statements)

References 10 publications

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“…This observation is in line with the main theory (first described by Bueche) that revolves around the preferential breaking of the higher-molecular-weight chains during strong deformations (like milling) in the absence of any chemical reactions. , According to this theory, polymer molecules that are subjected to strong shear deformations should first disentangle in order for flow to occur. However, the network is kept in place by the entanglements; thus, large tensions are built up at these entanglement points.…”

Section: Resultssupporting

confidence: 87%

“…Therefore, the observed degradation is based on probability, so it is also possible for lower-molecular-weight chains to break, but it is much less likely. This is why many authors, including Bueche and Baramboim, propose a “critical” molecular weight below which the probability for degradation becomes negligible for certain processing conditions. − Nevertheless, when the processing conditions change, also this critical molecular weight changes due to different externally applied forces or environmental conditions.…”

Section: Resultsmentioning

confidence: 99%

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Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

et al. 2020

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In this study, we report on the influence of mechanochemical activation on the chemical stability of amorphous solid dispersions made up of indomethacin and hydroxypropyl methyl cellulose (HPMC), poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone vinylacetate) (PVPVA), or Soluplus. In agreement with our recently published work, all applied carriers were found to be prone to polymer degradation. Covalent bonds within the polymers were cleaved and mechanoradicals were generated. Furthermore, decomposition of indomethacin was also observed but occurred only in the presence of polymers. Hence, it is proposed that the generated mechanoradicals from the polymers are responsible for the chemical degradation of indomethacin. Our study also strongly suggests the existence of a critical polymer- and process-dependent molecular weight limit “M ∞”, below which only limited mechanodegradation takes place since the lower-molecular-weight polymer PVP K12PF had a less profound influence on the degradation of indomethacin in comparison to PVP K25.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

et al. 2020

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“…The mechanism of polymer entanglement tearing most likely occurs in the earlier state of degradation during the high rate of shearing, via the strong elongated flow encountered by the polymer which may give sufficient energy to disrupt the molecules. 40 The results indicate that entanglement plus cavitation/free radicals are major contributions to the degradation of the polymer during earlier periods of microfluidization. Without concurrent UF treatment, the degradation rate constants are not significantly different between the earlier period and later period of the shearing treatment.…”

Section: Microfluidizationmentioning

confidence: 93%

“…39 Entanglement and stretch effects result from shearing. 32,40 Entanglement and stretch effects plus cavitation energy result from the microfluidization process. 36 -38 Therefore, the rate constant is higher for treatments at 30 • C than those at 0 or 50 • C for both ultrasonic and Polym Int 2011; 60: 897-902 c 2011 Society of Chemical Industry microfluidization treatments, because an elevated temperature facilitates the loss of cavitational energy.…”

Section: Solution Temperaturementioning

confidence: 99%

Differences in degradation kinetics for sonolysis, microfluidization and shearing treatments of chitosan

Chen

Huang

Tsai

et al. 2011

Polymer International

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Solution concentration, temperature, reaction time and use or non‐use of concurrent ultrafiltration treatment for fragment removal are factors that affect the degradation rate constant in sonolysis, microfluidization and shearing treatments. The cause of these operation conditions and their effect on chitosan degradation rate constant were compared. Different operation conditions for each treatment resulted in various solution viscosities, ease of dissipation of cavitation, entanglement and stretching, in turn resulting in different rates of effectiveness of degradation by different degradation mechanisms. A rationale for applying these physical methods in practical chitosan production is proposed. Copyright © 2011 Society of Chemical Industry

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“…The kinetics of ultrasonic scission can thus be directly ascribed to the implosion velocity of the cavitation bubbles and the length of the polymer that is fractured. The implosion velocity is dependent on the liquid properties, the content of the bubble, the acoustic pressure, and the static pressure, respectively . Therefore, it is important to know the phase composition, density, and viscosity of the liquid.…”

Section: Introductionmentioning

confidence: 99%

Influence of the CO₂Antisolvent Effect on Ultrasound-Induced Polymer Scission Kinetics

et al. 2005

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Ultrasound-induced polymer scission is a nonrandom process which alters the molecular weight distribution of polymers. However, transient cavitation, and consequently polymer scission, is not possible in concentrated polymer solutions due to the high liquid viscosity. The addition of an antisolvent can be used to circumvent this problem because the antisolvent decreases the gyration radius of polymer chains, which induces a reduction in liquid viscosity. To determine the influence of carbon dioxide (CO2) as an antisolvent on the ultrasound-induced scission rate, ultrasonic scission experiments of poly(methyl methacrylate) have been performed in bulk methyl methacrylate (MMA) as well as in CO2-expanded MMA. Modeling the experimental time-dependent molecular weight distributions (MWD) has revealed the scission kinetics at different polymer concentrations and CO2 fractions. At low polymer concentrations, the scission rate is decreased upon an increased CO2 content. This is a result of the higher vapor pressure of CO2, which cushions the cavitation. However, at higher polymer concentrations, this effect is counteracted by the viscosity reduction induced by CO2. As a consequence, the scission rate in CO2-expanded MMA is higher as compared to bulk MMA for solutions with a high polymer concentration. The results show that ultrasound-induced scission in pressurized CO2 can alter and control the MWD of polymers even in concentrated polymer solutions, whereas ultrasound-induced scission in bulk solutions is limited to relatively low polymer concentrations.

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Introduction

Cited by 17 publications

References 10 publications

Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

Differences in degradation kinetics for sonolysis, microfluidization and shearing treatments of chitosan

Influence of the CO₂Antisolvent Effect on Ultrasound-Induced Polymer Scission Kinetics

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Introduction

Cited by 17 publications

References 10 publications

Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

Mechanodegradation of Polymers: A Limiting Factor of Mechanochemical Activation in the Production of Amorphous Solid Dispersions by Cryomilling

Differences in degradation kinetics for sonolysis, microfluidization and shearing treatments of chitosan

Influence of the CO2Antisolvent Effect on Ultrasound-Induced Polymer Scission Kinetics

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Product

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Influence of the CO₂Antisolvent Effect on Ultrasound-Induced Polymer Scission Kinetics