Strain

crystallization Crystallization is a process that leads to solids with highly organized Atom, atoms or Molecule, molecules, i.e. a crystal. The ordered nature of a crystalline solid can be contrasted with amorphous solids in which atoms or molecules lack regu ...

is a phenomenon in which an initially amorphous solid material undergoes a phase transformation due to the application of strain. Strain crystallization occurs in

natural rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Types of polyisoprene ...

, as well as other

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus (E) and high failure strain compared with other materials. The term, a portmanteau of ''ela ...

s and

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s. The phenomenon has important effects on strength and fatigue properties.

How strain crystallization occurs

Strain crystallization occurs when the chains of

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s in a material become ordered during deformation activities in some polymers and elastomers. The three primary factors that affect strain crystallization are the molecular structure of the polymer or elastomer, the

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

, and the deformation being applied to the material. If a

's molecular structure is too irregular, strain crystallization can not be induced because it is impossible to order the chains of molecules. In order to induce strain crystallization, the polymer or elastomer is stretched while its temperature is kept above its

glass transition temperature The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rub ...

. It is also necessary for the yield point of the polymer to be exceeded by the stretching activity. This in turn will ensure that the chains of molecules are straightened. In general, the greater the deformation applied to the material, the higher the rate of crystallization.

Effects of strain crystallization

The

mechanical properties A material property is an intensive property of a material, i.e., a physical property or chemical property that does not depend on the amount of the material. These quantitative properties may be used as a metric by which the benefits of one mate ...

of materials are greatly affected by the orientation of the crystals in their micro-structure. The process of strain crystallization directly affects the micro-structure of the material by adding crystalline structures. Strain crystallization's effect on the micro-structure greatly increases the strength of the polymer or elastomer it is induced in. This effect of strain crystallization can be viewed in vulcanized natural rubber, a material that is known for its

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.stress.

Measuring strain crystallization

There are various techniques for measuring crystallization in rubber, including:

x-ray diffraction X-ray diffraction is a generic term for phenomena associated with changes in the direction of X-ray beams due to interactions with the electrons around atoms. It occurs due to elastic scattering, when there is no change in the energy of the waves. ...

specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...

changes, and

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

changes. Crystallization can also be observed indirectly through its effects on stress–strain and fatigue behavior.

References

Sources

*Chapter 1, Engineering with Rubber, Ed. A. N. Gent, Hanser, 1992. . *B. Huneau, STRAIN-INDUCED CRYSTALLIZATION OF NATURAL RUBBER: A REVIEW OF X-RAY DIFFRACTION INVESTIGATIONS, Rubber Chem. Technol. 84, 425 (2011); *Mars, W. V. (2009). Computed dependence of rubber's fatigue behavior on strain crystallization. Rubber Chemistry and Technology, 82(1), 51–61.
Chapter 10 – Strength of Elastomers
A.N. Gent, W.V. Mars, In: James E. Mark, Burak Erman and Mike Roland, Editor(s), The Science and Technology of Rubber (Fourth Edition), Academic Press, Boston, 2013, Pages 473–516, {{ISBN, 9780123945846, 10.1016/B978-0-12-394584-6.00010-8 *Rao, I,J; Rajagopal, K.R. (2001–02). "A study of strain-induced crystallization of polymers". ''International Journal of Solids and Structures. 38 (6-7): 1149-1167 https://doi.org/10.1016/S0020-7683(00)00079-2. ISSN 0020-7683.'' *Battjes, Kevin P.; Kuo, Chung-Mien; Miller, Robert L.; Saam, John C. (1995-05). "Strain-induced Crystallization in Poly ethyl3,3,3-trifluoropropyl)siloxane] Network". ''Marcromolecules'' 28 (3): 790-792
Strain-Induced Crystallization in Poly[methyl(3,3,3-trifluoropropyl)siloxane] Networks
ISSN 0024-9297 *Toki, S.; Fujimaki, T.; Okuyama, M. (2000–06). "Strain-induced crystallization of natural rubber as detected real-time by wide-angle X-ray diffraction technique". ''Polymer.'' 41 (14): 5423-5429
Strain-induced crystallization of natural rubber as detected real-time by wide-angle X-ray diffraction technique
ISSN 0032-3861. *"Crystallization". ''polymerdatabase.com''. Retrieved 2018-12-08. Rubber properties

How strain crystallization occurs

Effects of strain crystallization

Measuring strain crystallization

See also

References

Sources