Tensile Property Testing

Testing of tensile properties is probably the most widely used short-term mechanical test of all. This is because it is relatively easy to perform, gives reasonably reproducible results and yields a great deal of information. From this test one can obtain not only tensile strength, but also elongation and modulus.

Tensile properties are determined by stretching a test specimen at a constant rate. The resulting stress (or load applied) is measured an recorded as a function of strain (or elongation). The stress and strain are defined mathematically by:

Stress=     Load applied on specimen

                 Cross-section area of specimen

      Strain=    Increase in length of specimen

                                                          Original length of specimen

                                      Modulus=  Stress

                                                      Strain

Tensile strength is the maximum tensile stree which a material is capable of supporting. It is calculated from the maximum load carried during the tensile test and the original cross-sectional area of the specimen. If the tensile strength occurs at the sample's yield point, this stress is designated as the tensile strength at yield. if it occurs at the sample's break point, it is then designted the tensile strength at break 

The percentage of elongation at break is the ratio, expressed in percentage, of the extension (change in gauge length) at break point to the original gauge length multiplied by 100.

Polycaprolactone

Polycaprolactone (PCL) has been thoroughly studied as a substarte for biodegradation (Potts, 1984) and as a matrix in controlled-release systems for drugs (Pitt et al.,1980). Its degradation in vivo is much slower than that of poly (α-hydroxy acid). Thus, it is most suitable for controlled-release devices with long in vivo lifetimes. PCL is generally prepared from the ring-opening polymerization of ε-caprolactone.

PCL was chosen because of its good mechanical properties and its compatibility with many types of polymers, and because it is one of the more hydrophobic of the commercially available biodegradable polymer (Koleske, 1978)

Poly (lactic acid) (PLA)

Poly (lactic acid) (PLA) degrade biologically into acid, a product of the carbohydrate metaolism, and a importance as a substitute for the non-degradable thermoplastics has attracted a lot of attention in recent years.

PLA are of considerable interest as biodegradable polymers in medical applications and also potentially for use as environmentally friendly packaging materials. PLA is a thermoplastic, high strength, high modulus polymer which can be made from annually renewable resources to yield articles for use in either the industrial packaging field or the biocompatible/ bioabsorbable medical device market (Migliaresi et al., 1988).

PLA exists in L and D- form, which are optical isomers. PLA with large amount of L- form isomer is highly crystalline. In general, the crystallinity and biodegradability depend on the content of D0 form isomer (Zhang et al., 1993).