Self-healing polymeric materials: A review of recent developments

The plastic in microplastics: A review.

Regarding the activation of chemical reactions, today’s chemist is used to thinking in terms of thermochemistry, electrochemistry, and photochemistry, which is reflected in the organization and content of the standard physical chemistry textbooks. The fourth way of chemical activation, mechanochemistry, is usually less well-known. The purpose of the present review is to give a survey of the classical works in mechanochemistry and put the key mechanochemical phenomena into perspective with recent results from atomic force microscopy and quantum molecular dynamics simulations. A detailed historical account on the development of mechanochemistry, with an emphasis on the mechanochemistry of solids, was recently given by Boldyrev and Tkáčová.1 The first written document of a mechanochemical reaction is found in a book by Theophrastus of Ephesus (371-286 B.C.), a student of Aristotle, “De Lapidibus” or “On stones”. If native cinnabar is rubbed in a brass mortar with a brass pestle in the presence of vinegar, metallic mercury is obtained. The mechanochemical reduction probably follows the reaction:1-3 * To whom correspondence should be addressed. Telephone: ++49-89-289-13417. Fax: ++49-89-289-13416. E-mail: martin.beyer@ch.tum.de (M.K.B.); Telephone: ++49-89-12651417. Fax: ++49-89-1265-1480. E-mail: clausen-schaumann@ fhm.edu (H.C.-S.). † Technische Universität München. ‡ Institut für Strahlenschutz. § Current address: Munich University of Applied Sciences. HgS + Cu f Hg + CuS (1) Volume 105, Number 8

http://depa.fquim.unam.mx/amyd/archivero/MECANOQUIMICA_3426.pdf

Mechanochemistry: the mechanical activation of covalent bonds.

Mechanistic implications of plastic degradation

Polybenzoxazines-New high performance thermosetting resins : Synthesis and properties

For an ageing process involving the consumption of a small molecule (typically O2 or H2O) by reaction with the polymer, there are critical conditions of reaction rate and/or thickness above which the process becomes kinetically controlled by the diffusion of the small molecule in the polymer. Suitable lifetime prediction models must then involve the thickness distribution of reaction products. This latter can be predicted from Fick's law, modified by a term relative to the rate of consumption of the diffusing species by the chemical reaction. Some problems related to the use of this approach are examined here. It appears that, in the most frequent case, the thickness of the degraded layer is of the order of magnitude of D/k, where D is the diffusion coefficient and k the pseudo-first-order rate constant for reactant consumption. Some examples of application related to photochemical, radiochemical and thermochemical ageing are examined. It can, for instance, be shown that in photochemical or radiochemical ageing, the thickness of the oxidized layer (TOL) is proportional to the reciprocal of lβ, where l is the radiation intensity and Β an exponent depending essentially on the radical chain mechanism. It is generally expected that in the case of thermal ageing, the TOL is a decreasing function of the temperature. Some consequences of diffusion control on accelerated and natural ageing methods are briefly examined. The consequences of the ageing-induced “skin-core” structure due to the diffusion control are examined. The main features of the observed polymer embrittlement can be explained in terms of fracture mechanics.

Role of oxygen diffusion in polymer ageing: kinetic and mechanical aspects

The literature dealing with degradation-induced embrittlement mechanisms in semi-crystalline polymers having their amorphous phase in rubbery state is reviewed. It is first demonstrated that the decrease of molar mass resulting from a quasi-homogeneous chain scission process is responsible for embrittlement. The main specificity of the polymer family under study is that embrittlement occurs at a very low conversion of the degradation process, while the entanglement network in the amorphous phase is slightly damaged. In these polymers, chain scission induces chemicrystallization. The analyses of available data on this process show that it is characterized by a relatively high yield: about one half entanglement strands integrate the crystalline phase after one chain scission. A simple relationship expressing the chemicrystallization yield for a given polymer structure is proposed. Chain scission and chemicrystallization can lead to embrittlement through two possible causal chains: (1) chain scission → molar mass decrease → chemicrystallization → decrease of the interlamellar spacing → embrittlement. (2) Chain scission → molar mass decrease → chemicrystallization → decrease of the tie-macromolecule concentration → embrittlement. At this state of our knowledge, both causal chains are almost undistinguishable.

Review: degradation-induced embrittlement in semi-crystalline polymers having their amorphous phase in rubbery state

Factors governing water absorption by composite matrices

The solubility and diffusivity of water at 100° C, 95% relative humidity were studied for 14 stoichiometric epoxide-amine networks based on epoxide or amine mixtures Neither the packing density nor the glass transition temperature nor the crosslink density seemed to play a significant role The water absorption is essentially linked to the concentration of polar structures, but also decreases with the extent of intramolecular hydrogen bonding This can be accurately predicted using a simple additive relationship The diffusivity decreases with the hydrophilicity and packing density, but in a complex way probably involving the nature of hydrogen bonds between the water and the substrate

Jacques Verdu

Papers

Role of oxygen diffusion in polymer ageing: kinetic and mechanical aspects

Review: degradation-induced embrittlement in semi-crystalline polymers having their amorphous phase in rubbery state

Factors governing water absorption by composite matrices

Structure-properties relationships for densely cross-linked epoxide-amine systems based on epoxide or amine mixtures

Mechanism of degradation induced embrittlement in polyethylene