Question

1.What are the distinctive features between a polyester and vinyl ester in terms of their properties.

2.List five (5) general characteristics of fiber re-enforced composites over their metal counterparts.

please no hand writing.

Answer 1

polyester	vinyl ester
Polyester resins are formed by the reaction between polyols such as glycol or ethylene glycol with dibasic acids such as phthalic acid or maleic acid.	Vinyl ester resins are produced by the reaction ('esterification') between an epoxy resin and an unsaturated monocarboxylic acid.
These unsaturated resins are combined with other chemicals sometimes called hardeners or catalysts.Methyl ethyl ketone peroxide ('MEKP') is one such 'hardening' agent.	Essentially they comprise a base of polyester resin strengthened with epoxy molecules in the backbone of the molecular chain.Vinyl esters also use peroxides (e.g. MEKP) for hardening.
polyesters have High Viscosity	vinyl esters are midway between polyesters and epoxy resins in terms of Viscosity
polyesters are less tolerant of stretching than Vinyl esters.	Vinyl esters are more tolerant of stretching than polyesters.This makes them more able to absorb impact without damage. They are also less likely to show stress cracking.
polyesters shrink more on curing	Vinyl esters shrink less on curing, which means that 'pre-release' of a laminate from a mold is less significant.
polyesters are stronger resistance to ambient conditions	Vinyl esters are less sensitive to ambient conditions (temperature and humidity) than are polyesters
The cross bonding of polyesters. is less superior to that of vinyl esters	The cross bonding of vinyl esters is superior to that of polyesters.
polyesters are cheaper than Vinyl esters	Vinyl esters are more expensive than polyesters

2) Some key characteristics of composites that make them so useful are:

1) Specific strength : This is simply the rigidity or hardness of a material with regard to its weight. For example,   a number of composites such as fiberglass share comparable impact resistance (bangability) with steel and   titanium at a fraction of the weight employed.

2) Expense:Many composites can be manufactured with less cost than their traditional metal counterparts.

3)Application : Because composites are composed of 2 or more "phases", they can be formulated to meet the needs of a specific application with considerable ease.

4) Processability : As most of you know, metal processing requires high amounts of thermal energy (heat). Plastics and plastic based composites require less heat to mold or process the products.

5) Bonding/Blending of composites

general Charactersistics :

Amount of Fibres

Orientation of Fibres

Types of Fibres

Fiber Aspect Ratio

Fibre Orientation Effect

Strain rate effects

Type Of matrix

Interfacial Bonding Conditions