Fracture and Orientation of Long‐Glass‐Fiber‐Reinforced Polypropylene During Injection Molding

Abstract

Injection processing parameters directly influence the final fiber length and may have a negative effect on the mechanical properties of a part. The aim of the work is to investigate and quantify the effects of the injection rate (2/10/50 cm3/s) on the fiber length, the distribution, and orientation during injection molding and the mechanical properties of long‐glass‐fiber‐reinforced polypropylene (LGF/PP) by experimental and simulated methods. When the injection rate increases from 2 to 10 cm3/s, the fiber length sharply decreases from the original 11 mm to 3.43 mm at the nozzle and 1.30 mm at the filling end, and almost 88% of the fibers are less than 3 mm when the injection rate is 50 cm3/s. A distinct hierarchical orientation (skin‐shear‐core) for the fiber distribution in the thickness is obtained via a metallographic microscope, which shows that the shear layer (here the shear stress is larger and the fiber is more inclined to oriented along the flow direction) decreases with increasing injection rate. Moreover, the numerical results of the residual fiber length and orientation at different injection rates are in accord with the trend of the measured results. POLYM. ENG. SCI., 60:13–21, 2020. © 2019 Society of Plastics Engineers

The Low Breaking Fiber Mechanism and Its Effect on the Behavior of the Melt Flow of Injection Molded Ultra-Long Glass Fiber Reinforced Polypropylene Composites

“…Rohde et al showed that the back pressure has a detrimental effect on both the fiber length and the impact energy absorbance of L-FRP specimens [ 16 ]. Kumar et al investigated the effects of the injection pressure and screw speed on two thermoplastics compounded with different initial fiber lengths [ 17 , 18 , 19 , 20 ]. The results showed that an understanding of the orientation behavior of the fibers in the injection molding process is critical.…”

Comparative Analysis of the Impact of Additively Manufactured Polymer Tools on the Fiber Configuration of Injection Molded Long-Fiber-Reinforced Thermoplastics

“…This specific orientation pattern is well-known and caused by the fountain flow effect. However, the numerical predictions of Hou et al [34] do not match with the empirical orientation in the skin layer. Parveen et al [37] achieved comparable results to Hou et al on a disc geometry (2 mm; 75 mm D) and stated that a higher fiber length leads to a wider core region with more fibers aligned transverse to the flow direction at the end of the flow path.…”

“…The results are consistent with Seong et al [33], who noted an increase in Young's modulus, melting temperature, and viscoelastic properties, and a less uniform distribution of the fiber with an increasing fiber length. Hou et al [34] measured a reduction of the average fiber length with an increasing injection rate over the whole length of tensile specimens. Based on the work of Tadmor [35] as well as Osswald and Menges [36], there are seven characteristic regions that can be differentiated in injection molded parts, each with a specific fiber orientation.…”

In Situ Microfibril Structure in Incompatible Isotactic Polypropylene/Polylactic Acid Blends Controlled By Viscosity Ratio

“…Recently, microfibril composites (MFCs) have attracted much attention of many researchers, as the mechanical strength of MFC is typically 30%–50% higher than the calculated values of the rule of mixtures . It is different from traditional filler, such as glass fiber , carbon fiber , and so forth, the reinforced microfibrils in MFC are formed during processing . Therefore, some shortcomings in traditional fiber reinforced composites can be weakened or even be avoided, for example, the wear of processing machinery will be reduced due to the relatively low viscosity of the polymer blends.…”