**9. References**

210 Thermoplastic Elastomers

laminates. However, in tests under the same conditions on body armor without polymeric matrix (four layers of aramid fabric), a trauma depth of 11 mm was observed, which is 27% greater than that of the laminates with polymeric matrix. Images of an impacted armor-plating without a matrix are shown in Fig. 23, where it can observe more clearly the diamond-shaped

Table 3 presents the values of impact energy and trauma depth generated in the materials. It is important to remember that the maximum trauma depth permitted by the standard is 40 mm. These results demonstrate that the presence of the PP matrix improves posterior deformation of a material even though its configuration allows flexibility, as in the case of independent laminates. In contrast, absence of the matrix increases posterior deformation by 27%. It is also important to take into consideration that the presence of a witness material in contact with the back of the laminate reduces the ballistic limit of the aramid/PP composite

impact formation, as well as a more pronounced impression of the projectile.

Fig. 23. Four layers of aramid fabric without PP tested with witness material

aramida/PP consolidated 30.6 8.2 aramida/PP independent 30.6 8.13 aramida without matrix 30.6 11 Table 3. Ballistic properties of armor plating tested in presence of witness material

Configuration Impact energy (J) Trauma depth (mm)

A comparative study of two arrangements tested at high velocity impact was carried out to highlight improvements conferred by a polypropylene matrix to aramid fibers. Two arrangements were made of plain woven aramid fibers/PP, with consolidated and independent configurations. As observed in this work, the presence of the PP matrix generated advantages, such as a reduction in trauma depth in both cases in comparison to the sample without the PP matrix, where the independent laminates presented more back deformation but higher energy absorption than the consolidated laminates. Another advantage that needs to be evaluated, is the protection the matrix confers to the aramid against humidity and substances that may degrade it, such as UV light, thereby extending

material by 20%.

**7. Conclusions** 

its lifespan.


**11** 

*Portugal* 

**Thermoplastics** 

Mónica Oliveira, Victor Neto,

**Microinjection Molding of Enhanced** 

Injection molding is, nowadays, a well known and wildly used manufacturing process to produce both thermoplastic and thermosetting polymeric material components, in a large scale, with accuracy and at low prices. Even though the electronics industry provides an economy of scale for the silicon industry, polymer devices can be produced in huge volumes maintaining the requested features and quality, with a great variety of material characteristics, a fact that has considerably open the market to injection molding of micro-

A simple miniaturization/rescale of the conventional injection molding process is not valid due to problems related with the rheology of the polymer flow in the micro cavity/channel and requires that all the process layout, as well as adjacent technologies, should be reconsidered, enhanced and properly adapted. The dimensional reduction of the components requires a higher control of the overall accuracy of the devices. The molding blocks of this type of objects are bounded to an amplified wear due to the fact that the surface roughness is dimensionally very close to the dimensions being controlled. The wear of the molding surfaces and the adhesion forces involved in the part extraction stage are greatly influenced by the nature of the material being injected and are enlarged when the molded object shrinks in the core or in the pins of the molding blocks. This is even more critical due to the flow behavior of enhanced polymer materials, developed for highly demanding applications in what concerns material mechanical or chemical properties.

Tailored special polymers are of fundamental importance in the supplement of microcomponents. Complex polymeric materials engineered to detain both the mechanical properties and the memory shape suitable for applications such as active control, impose

In conventional injection molding tools, surface engineering is used to improve the molding block performance to obtain parts with superior mechanical quality. In micromolding, surface engineering has a more important role due to the above-sited requisites, in order to reduce the deterioration of the molding impressions, increase its durability and reduce the need for corrective intervention on the tool. Different thin film coatings may be used, but

enormous challenges in what concerns both the process and the molding tools.

**1. Introduction** 

components.

 Maria Fonseca, Tatiana Zhiltsova and José Grácio *Department of Mechanical Engineering, University of Aveiro* 

Michael, Piggott. (2002), Load Bearing Fibre Composite, Kluwer Academic

