**1. Introduction**

On the market volume basis of standard plastics, polypropylene occupies the second position after various polyethylenes (HDPE, LDPE, and LLDPE) and is expected to rise by 3% per year by 2024 according to the recent report by Ceresana [1]. Following PlasticsEurope about 9.9 m of PP were demanded in 2017 for food packaging, sweet and snack wrappers, hinged caps, microwave containers, pipes, automotive parts, bank notes, etc. in Europe [2]. The success of polypropylene derives from the proper balanced physical and chemical properties with a combination of many factors, such as low density, excellent thermal stability, good chemical resistance, high crystallinity, and high stiffness or hardness with a wide design flexibility and simplicity of recycling making PP an attractive construction material. Owing to plausible melt rheology and thermal properties, PP-based materials are compatible with many processing technologies and can be processed by injection molding, film blowing and casting, extrusion of woven non-woven fabrics,

fiber spinning, and calendering [3, 4]. Also polypropylene composites for injection molding represent a sector of production for applications where higher stiffness and hardness are required. These higher mechanical properties are often obtained by addition and dispersion of particulate fillers and/or glass fibers [5].

Depending on the process and applications, various grades of polymer are properly selected and defined by melt flow index (MF) that represents the output of polymer expressed in g/10 mins during a vertical extrusion and measured in standard conditions, usually at 230°C and load of 2.16 kg with a diameter die of 2.096 mm [6]. @@@Melt flow grades in the range 0.3–2.0 are chosen for pipes, sheets, and blow molding, whereas higher grades between 2 and 8 are selected for film and fiber production. Higher fluidity polymers with MF above 8 are typically used for injection molding and extrusion coating [7]. Common MF for woven nonwoven (WNW) fabrics is usually in the range 18–25.

During various processing conditions, polymer chains are oriented, and the final properties directly depend on the combined interaction of polymer crystallized and amorphous phases during shear flow and/or elongational flow. The latter is typically dominating in film and fiber production. In particular, it is possible to achieve a high extension of macromolecular chains due to the relatively easy spinning, with a very high level of alignment [8, 9]. According to Kunugi, experimental maximum modulus and strength of about 40 and 1.5 GPa, respectively, could be obtained for highly extended helix crystallizing polymer [10]. In the case of injection molded polypropylene, an extensive work has been published with specific details on the effect of macromolecular orientation on polymer structure, after process, characterized by XRD, DSC, and DMTA in dependence on various factors, such as skin layer, filler effect, copolymers, flow direction, processing parameters, etc. [11].

In this chapter both injection molded samples and fiber-based products are compared as function of polymer processing. Mechanical, thermal, and structural analyses are presented. Particular attention will be spent on interpretation of X-ray analysis on fiber oriented polymers, comparing results before and after mechanical and creep tests.
