Duromers

Duriron Duromer Durometer hardness test Duroquin Duro Sup er Glue Duro-Tak... 

Table 10. Comparison of Characteristic Properties of CD-Modified BPA-Polycarbonate with UV-Curing Duromer...

Duromers (cross-linked polymers) based on highly reactive resins with short setting times. 

Hardness basically is the resistance to indentation as measured under specific conditions such as depth of indentation, load applied, and time period. Different tests relate to different hardness behaviors of plastics. They include Barcol, Brinell, durom-eter, Knoop, Mohs, Rockwell, Shore, and Vicat (2). 

By far the largest quantity of asbestos is utilized in asbestos composites for reinforcing inorganic (cement) and organic (PVC, rubber, duromers) binders. Whereas the consumption in Western industrialized countries has declined steeply (95% in the USA banned in FRG since 1993), more than 2 10 t of asbestos was processed worldwide in 1997 mainly to building materials made from asbestos cement, which were utilized in Asian and Eastern European countries and in developing countries. 

ISO 868, Plastics and ebonite - Determination of indentation hardness b means of a durom-eter (Shore hardness), 1985. 

In this chapter we review the physical properties of liquid crystalline elastomers using publications until 1996. For a review of the physical properties of strongly cross-linked liquid crystalline polymers, which give rise to anisotropic nonliquid crystal line materials (duromers or anisotropic solids) we refer to the recent review by Hikmet and Lub [1]. 

The influence of the crosslinking density on the birefringence has been studied [11]. For weakly crosslinked materials the results obtained coincide with the previous ones while for strongly crosslinked liquid crystalline elastomers the birefringence is only weakly affected in the vicinity of the phase transition as can be seen in Fig. 17. We stress, however, that the strongly crosslinked LSCE are duromers for which there are no independent macroscopic director degrees of freedom anymore, which are characteristic for the nematic liquid crystalline phase in low molecular weight materials, in sidechain polymers and in weakly crosslinked liquid crystalline elastomers. 

This polyvinyl chloride compound family is highly elastomeric and exhibits a dry non-tacky surface even at hardnesses as low as 40 Shore A durom-eter. Their rubber-like resilience, high elongation and low permanent set and fatigue resistance offer advantages over conventional formulations (Tables 4.6, 4.12, and 4.13). 

Hardness. Hardness is probably the least difficult and most often measured property of vulcanized elastomers. It is in almost every fist of rubber specifications. As measured, hardness is the relative resistance of the rubber surface to deformation by an indentor. The hardness of rubber is measured by using a small spring-loaded gauge known as a durome-ter (ASTM D 2240). One measures the hardness by pressing the indentor against the rub-... 

Highly cross-linked Duromer Non-meltable, insoluble, non swellable, at room temperature hard and stiff solids EP, UP... 

Application at T < Tg polymer hard, stiff, brittle, thermoplastics, duromers. 

Usually, pol5dmide is a duromer, but it can also form a thermoplastic. The glass transition temperature is valid for the latter state. 

Elastomers and duromers are always completely amorphous because the chemical bonds make a regular arrangement of the chain molecules impossible. Thermoplastics, on the other hand, can be semi-crystaUine i. e., contain a mixture of crystalline and amorphous regions. The volume fraction of the crystalline regions in a semi-crystaUine thermoplastic is called its crystallinity. 

In some duromers, the molecular network is formed not by cross-linking the chains but directly from the monomers. Strictly speaking, in this case it is not possible to talk of cross-linked chains. 

As already discussed in section 1.4, we distinguish amorphous and semicrystalline thermoplastics, elastomers and duromers. All explanations given in the following relate to amorphous thermoplastics, unless noted otherwise. The peculiarities of the other groups are discussed separately. 

Duromers and elastomers also exhibit a glass transition temperature with melting of the non-covalent intermolecular bonds, with localised sliding of the molecules being consequently easier. However, due to the covalent bonds between the molecules, it is not possible to pull single molecules out of the molecular network. Thus, these materials never become viscous liquids, but always remain solid. It is not possible to heat them to temperatures where the covalent intermolecular bonds are molten because they will decompose before. 

The elastic behaviour of polymers is mainly determined by the intermolecular bonds between the chain molecules, not by the covalent bonds within. For elastomers and duromers, the covalent bonds linking the chains are also relevant. In the following, we will start by discussing the elastic properties of thermoplastics and afterwards study the influence of cross-linking. 

Elastomers and duromers are characterised by additional covalent cross-links between the chain molecules. In the energy-elastic regime, these additional bonds do not influence the elastic properties significantly Young s modulus only increases slightly. 

If the cross-linking density of a polymer is increased further, the entropy-elastic behaviour vanishes nearly completely because the large number of crosslinks prevent the straightening of the molecules. For this reason, duromers show only a small decrease of Young s modulus with temperature (see figure 8.10(d)) caused by relaxation processes. They are energy elastic even above the glass temperature. 

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