**2. Experimental**

### **2.1 Products and polymers**

Various products of PPs with different MF in the range 3.6 and 18 g/10 mins were selected and analyzed for the comparative evaluation of the effect of process on properties and orientation. The higher the molecular weight, the lower the melt flow. **Figure 1** shows the empirical relation between molecular weight and melt flow according to literature data [12] and Eq. (1):

$$
\log \text{MW} = 2.47 - 0.234 \log \text{MF} \tag{1}
$$

**93**

**Figure 1.**

**Table 1.**

*Effect of Processing and Orientation on Structural and Mechanical Properties of Polypropylene…*

and 230°C). Due to the anisotropy of the process, fabrics were tested in machine direction (MD) and cross direction (CD) [13]. Normalized thickness of samples for mechanical testing was obtained assuming 0.905 g/cm as bulk density of polymer. BCF of 64 filaments with the total titer of 1150 dtex [14] and equivalent diameter of 403 μm were industrially produced by Aquafil Spa (Arco, TN, Italy) by using

*Relation between melt flow index and molecular weight. The value of various products are indicated, i.e., woven non-woven (WNW), bulk continuous filaments (BCF), injection molding (IM), and fiber spinning (FS).*

**Code Product MF g/10 mins Process** FS Monofilament 3.6 Fiber spinning IM Dumbbell 8.5 Injection molding WNW Fabrics 18 Woven non-woven spunbonding BCF Multifilament 10.0 Bulk continuous filament spinning

Monofilaments of PP and composite fiber were produced in lab-scale starting from commercial pellets (Sabic PP505P with MF = 3.6 g/10 mins at 2.16 kg and 230°C) and kaolinite masterbatch (Paralux by Vale, Brazil). Polypropylene fibers containing kaolinite in the range 1–30 wt% were manufactured by a two-step process, i.e., compounding/melt spinning and hot drawing. Melt-compounding was performed in a corotating intermeshing twin-screw extruder Rheomix Thermo Haake PTW16 (L/D 25; D = 16 mm; rod die 1.65 mm; temperature profile 130–230°C). Drawing of extruded filaments with 500 μm diameter was set at 145°C in order to produce single fiber at increasing draw ratio (DR) in the range 5–15. More details of compounding-spinning-drawing processes are described in literature [15, 16].

Tensile tests were performed on dumbbell ASTM specimens (Section 3.2 × 12.7 mm), BCF multifilaments (200 mm length), and WNW fabrics (50 mm width and 200 mm

PP with melt flow of 10 g/10 mins (2.16 kg, 230°C).

*Products obtained from polypropylene of different melt flow.*

**2.2 Mechanical and thermal tests**

*DOI: http://dx.doi.org/10.5772/intechopen.85554*

where MW is the molecular weight expressed in kDalton and MF is the melt flow measured in standard conditions (230°C and 2.16 kg). The MF value of polypropylene of various products is also reported. See details in **Table 1**.

Dumbbell specimens ASTM type (3.2 thickness, 12.7 width) were obtained by injection molding machine Arburg 320 C type Allrounder 500–250 (screw 35 mm) from iPP HP551M (Basell, Ferrara; MF ≈ 8 g/10 mins). Processing conditions were injection velocity of 40 cm3 /s, melt temperature (nozzle) of 240°C, and injection pressure 1100 bar.

WNW fabrics with surface density of 80 g/m<sup>2</sup> were spunbonded by Texbond Spa (Rovereto, TN, Italy) by using iPP with melt flow of 18 g/10 mins (at 2.16 kg *Effect of Processing and Orientation on Structural and Mechanical Properties of Polypropylene… DOI: http://dx.doi.org/10.5772/intechopen.85554*

#### **Figure 1.**

*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

by addition and dispersion of particulate fillers and/or glass fibers [5].

woven (WNW) fabrics is usually in the range 18–25.

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

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 non-

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.

Various products of PPs with different MF in the range 3.6 and 18 g/10 mins were selected and analyzed for the comparative evaluation of the effect of process on properties and orientation. The higher the molecular weight, the lower the melt flow. **Figure 1** shows the empirical relation between molecular weight and melt flow

log MW = 2.47–0.234 log MF (1)

where MW is the molecular weight expressed in kDalton and MF is the melt flow measured in standard conditions (230°C and 2.16 kg). The MF value of poly-

Dumbbell specimens ASTM type (3.2 thickness, 12.7 width) were obtained by injection molding machine Arburg 320 C type Allrounder 500–250 (screw 35 mm) from iPP HP551M (Basell, Ferrara; MF ≈ 8 g/10 mins). Processing conditions were

Spa (Rovereto, TN, Italy) by using iPP with melt flow of 18 g/10 mins (at 2.16 kg

/s, melt temperature (nozzle) of 240°C, and injection

were spunbonded by Texbond

propylene of various products is also reported. See details in **Table 1**.

**92**

**2. Experimental**

**2.1 Products and polymers**

injection velocity of 40 cm3

pressure 1100 bar.

according to literature data [12] and Eq. (1):

WNW fabrics with surface density of 80 g/m<sup>2</sup>

*Relation between melt flow index and molecular weight. The value of various products are indicated, i.e., woven non-woven (WNW), bulk continuous filaments (BCF), injection molding (IM), and fiber spinning (FS).*


#### **Table 1.**

*Products obtained from polypropylene of different melt flow.*

and 230°C). Due to the anisotropy of the process, fabrics were tested in machine direction (MD) and cross direction (CD) [13]. Normalized thickness of samples for mechanical testing was obtained assuming 0.905 g/cm as bulk density of polymer.

BCF of 64 filaments with the total titer of 1150 dtex [14] and equivalent diameter of 403 μm were industrially produced by Aquafil Spa (Arco, TN, Italy) by using PP with melt flow of 10 g/10 mins (2.16 kg, 230°C).

Monofilaments of PP and composite fiber were produced in lab-scale starting from commercial pellets (Sabic PP505P with MF = 3.6 g/10 mins at 2.16 kg and 230°C) and kaolinite masterbatch (Paralux by Vale, Brazil). Polypropylene fibers containing kaolinite in the range 1–30 wt% were manufactured by a two-step process, i.e., compounding/melt spinning and hot drawing. Melt-compounding was performed in a corotating intermeshing twin-screw extruder Rheomix Thermo Haake PTW16 (L/D 25; D = 16 mm; rod die 1.65 mm; temperature profile 130–230°C). Drawing of extruded filaments with 500 μm diameter was set at 145°C in order to produce single fiber at increasing draw ratio (DR) in the range 5–15. More details of compounding-spinning-drawing processes are described in literature [15, 16].

#### **2.2 Mechanical and thermal tests**

Tensile tests were performed on dumbbell ASTM specimens (Section 3.2 × 12.7 mm), BCF multifilaments (200 mm length), and WNW fabrics (50 mm width and 200 mm

length) by using a dynamometer Instron mod. 4502 with a crosshead speed of 100 mm/min. WNW fabrics were tested both in machine and in cross direction. Single fibers of 10–20 mm were tested with a crosshead of 5–10 mm/min.

Differential scanning calorimetry was performed on PP specimens of about 15 mg by means of a Mettler DSC30 calorimeter by thermal cycling in the range 0–220°C with a heating/cooling rate of 10°C/min. Melting and crystallization temperature/peak were registered. The crystallinity X was determined referring the measured melting enthalpy ∆Hi in the first heating scan to 207 J/g and the standard enthalpy of the fully crystalline PP according to Eq. (2):

$$\mathbf{X} = \mathbf{100}\,\Delta\mathbf{H}\_i/2\mathbf{0}\mathbf{\mathcal{T}}.\tag{2}$$

DMTA-thermal creep specimens of WNW (stripes 20x5 mm) and BCF (15 mm length) were subjected to dynamical mechanical analysis in tensile mode by using a DMTA Mk II (Polymer Laboratories) with a dynamic deformation of 11 μm, frequency of 5 Hz, static stress between 1 and 16 MPa, and heating rate of 3°C/min in the range −50/120°C. Storage (E') and loss (E") moduli are reported as a function of temperature. Thermal creep (TC) was also evaluated according to Eq. (3):

$$\text{TC} = \text{100}^\* \{ \Delta \text{L/L}\_0 \} \tag{3}$$

where ∆L is the specimen length variation and L0 is the initial length.

Isothermal creep at 25°C was performed on samples 200 mm length (and 50 mm width for WNW fabrics) by applying for 30 mins a constant stress of 16 MPa for BCF and 3.5 MPa for WNW, and a following recovery for 30 mins at a minimum stress of 1.5 MPa for BCF and 0.05 MPa for WNW, respectively. WNW fabrics were tested both in machine and cross direction.

#### **2.3 Fiber diffraction measurements**

All diffraction images were collected in transmission using a modified Laue camera with a removable image plate 24 × 15 cm2 with a pixel size of 43 microns at a distance from the sample equal to 8.81 cm. The sample to detector distance

#### **Figure 2.**

*Fiber diffraction raw images for the PP fibers with 10 wt% kaolinite (K10). (a) As-span fibers showing smoother texture. (b) Fibers at DR = 10: the central spots radially dispersed are due to diffraction from the residual bremsstrahlung radiation in the filtered only X-ray beam. Sharper spots are produced by the PP strong fiber texture, and more continuous circles are from kaolinite diffraction.*

**95**

**Figure 3.**

*for comparison.*

*Effect of Processing and Orientation on Structural and Mechanical Properties of Polypropylene…*

was calibrated through a Si standard powder packed between two Mylar films and stretched by the same fiber diffraction sample holder used for the polymers.

The beam (CuKα radiation at 40 kV and 30 mA) was collimated through a pinhole and a Ni filter to ensure a proper resolution in the images and sufficient beam intensity. Only one diffraction image per sample was sufficient to get all the crystal,

In **Figure 2(a)** and **(b)**, two of these diffraction images are shown for the PP fibers with kaolinite filler. The two images enlighten how easily the differences in texture can be caught by the fiber diffraction technique. Not only the quality of the texture can be appreciated but also a quantitative analysis can be done by a proper methodology shown in the following paragraph. From the two images, we can also see some artifacts originated from the not strictly monochromatic beam (diffrac-

The effect of orientation of various polypropylene products can be firstly evaluated by the different mechanical properties; in particular modulus and maximum

Dumbbell specimens exhibited a tensile modulus of 950 ± 9 MPa, yield stress of 33 ± 1 MPa, and stress and deformation at break of 15 ± 2 MPa and 73%, respectively. Mechanical properties are quite different from other products, even if molecular weight is quite similar to BCF products. In injection molding, chain alignment and solidification follow a different pattern with respect to the fiber formation during spinning, and consequently dumbbell specimens exhibit heterogeneity in macromolecular orientation with a skin effect and a disordered core structure, as well described in literature [11]. Moreover, it should be considered that the shape factor, calculated as the ratio between the perimeter and section, is lower for IM

*Comparison of mechanical properties (tensile modulus and strength) of various oriented products, such as WNW, undrawn fibers from WNW, BCF, and drawn fibers with DR = 10; selected data of PP fibers or nanocomposite fibers with 10 (K10), 20 (K20), and 30% (K30) of kaolinite. Data of IM sample are also shown* 

for WNW, 80 mm<sup>−</sup><sup>1</sup>

for FS depending on the drawing. The efficiency of chain orientation

for BCF, and in the range

tion of the bremsstrahlung), but we account for them in our analysis.

*DOI: http://dx.doi.org/10.5772/intechopen.85554*

**3. Results and discussion**

**3.1 Mechanical properties**

(0.8 mm<sup>−</sup><sup>1</sup>

of 8–31 mm<sup>−</sup><sup>1</sup>

texture, and microstructure information needed.

stress (strength) are summarized in **Figure 3**.

) with respect to 160 mm<sup>−</sup><sup>1</sup>

### *Effect of Processing and Orientation on Structural and Mechanical Properties of Polypropylene… DOI: http://dx.doi.org/10.5772/intechopen.85554*

was calibrated through a Si standard powder packed between two Mylar films and stretched by the same fiber diffraction sample holder used for the polymers.

The beam (CuKα radiation at 40 kV and 30 mA) was collimated through a pinhole and a Ni filter to ensure a proper resolution in the images and sufficient beam intensity. Only one diffraction image per sample was sufficient to get all the crystal, texture, and microstructure information needed.

In **Figure 2(a)** and **(b)**, two of these diffraction images are shown for the PP fibers with kaolinite filler. The two images enlighten how easily the differences in texture can be caught by the fiber diffraction technique. Not only the quality of the texture can be appreciated but also a quantitative analysis can be done by a proper methodology shown in the following paragraph. From the two images, we can also see some artifacts originated from the not strictly monochromatic beam (diffraction of the bremsstrahlung), but we account for them in our analysis.
