CompositesWorld
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CompositesWorld.com 27 NEWS N E W S N S N E W S E N W S W this study, due to its good processability, resistance to organic solvents and its hydrophobic quality. But David Purcell, Zoltek's executive VP, says that ulti- mately, "we opted for carbon fber and polyamide 6 [PA6] as that combination is a common request from the automotive industry." PP, he explains, typically exhibits relatively lower mechanical properties and service temperatures when compared to an engineered thermoplastic, such as PA6. So, despite PA processing drawbacks, such as higher processing temperatures (see Tables 1 & 2, this page) and greater water absorption, it was judged the better candidate for the intended purpose. Specifcally, Zoltek's Panex 35 (50K) carbon fber and a PA6 thermoplastic matrix from an unspecifed source were selected for the experi- ments conducted in the study. LFT processing technologies vary, and the type of technology afects the end properties in the part. One type uses glass mat reinforcement commin- gled with glass thermoplastic sheets. Another, indirect LFT processing, uses pellets for injection molding. Relatively new direct LFT technology combines the fber and matrix immediately before the compound enters the mold; the compound can then be processed either by direct injection molding (LFT-D-IMC) or by extruder compression molding (LFT-D-ECM). LFT-D-ECM was selected for this study because, frst, unlike other LFT systems, it uses two extruders and, thus, separates the compounding and fber- mixing steps. Terefore, both extruders can be individually optimized for their specifc functions. Second, the material is not subjected to the same high levels of stress typical in injection molding, and, therefore, there is less fber breakage and, in turn, better mechanical properties in the part. Immediate improvement Fifteen experiments were run for the study, each with diferent processing conditions (Table 3, p. 28), but the parameters for all were constant (See Table 4, p. 28). Te study concluded that the selected carbon fber/polyamide D-LFT material system provided immediate improvement in mechanical properties compared with glass fber D-LFT, especially in stif- ness (tensile modulus, or modulus of elasticity, the measure of tensile stress to elongation). "Tensile strength will be lower than it is in a continuous fber format, but in automotive parts and consumer electronics applications, modulus is actually more critical for meeting specifc stifness design requirements," Purcell explains, "and stifness Carbon Fiber in D-LFT Material Tested Weight % Specifc Strength (E/ρ) (Mpa/ (g/cm 3 )) Comparison vs. Carbon/ PA6 Tensile strength: Carbon/PA6 35 104.0 N/A Tensile strength: E-glass/PA6.6 (Krause, Henning, Troster, Geiger, & Eyerer, 2003) 30 71.7 (83.65) -19.5% Tensile strength: E-glass/PP (Ernst, Henning, & Robbins, 2009) 40 54.0 (47.25) -54.5% Tensile strength: OEM-approved, 12.5-mm E-glass/PP pellets (Ernst, Henning, & Robbins, 2009) 40 40.0 (35) -66.3% Flexural strength: Carbon/PA6 35 174.5 N/A Flexural strength: E-glass/PP (Ernst, Henning, & Robbins, 2009) 40 92.4 (80.9) -53.6% Flexural strength: OEM-approved, 12.5-mm E-glass/PP pellets (Ernst, Henning, & Robbins, 2009) 40 63.3 (55.41) -68.2% Table 1 Comparison of strength of carbon fber/PA6.6 D-LFT vs. glass fber/PA6.6 D-LFT. Source (all tables/fgures) | "Mechanical Study of Direct Long Fiber Thermoplastic Carbon/Polyamide 6 and Its Relations to Processing Parameters," by K. Rohan, T.J. McDonough (Zoltek); V. Ugresic, E. Potyra and F. Henning (Fraunhofer Project Centre) Material Tested Weight % Specifc Modulus (E/ρ) (Gpa/(g/ cm 3 )) Comparison vs. Carbon/ PA6 Tensile modulus: Carbon/PA6 35 11.3 N/A Tensile modulus: E-Glass/PP (Ernst, Henning, & Robbins, 2009) 40 4.62 (4.04) -94.6% Tensile modulus: OEM-approved, 12.5-mm E-glass/PP pellets (Ernst, Henning, & Robbins, 2009) 40 3.26 (2.85) -128.1% Flexural modulus: Carbon/PA6 35 13.0 N/A Flexural modulus: E-glass/PP (Ernst, Henning, & Robbins, 2009) 40 3.35 (2.93) -126.4% Flexural modulus: OEM- approved, 12.5-mm E-glass/ PP pellets (Ernst, Henning, & Robbins, 2009) 40 3.50 (3.06) -123.8% Table 2 Comparison of modulus of carbon fber/PA6,6 D-LFT vs. glass fber/PA6,6 D-LFT. • Items in parenthesis have been linearly normalized to 35 wt-% for comparison purposes. • All specimens other than the OEM pellets were manufactured using the D-LFT-ILC or D-LFT-EMC process; tensile E-glass/PA6 was not reported by Krause (Krause, Henning, Troster, Geiger and Eyerer, 2003). • Densities: PP — 0.946 g/cm 3 , PA6 — 1.13 g/cm 3 , PA6.6 — 1.14 g/cm 3 , carbon — 1.81 g/cm 3 , E-glass — 2.55 g/cm 3 . • Items in parenthesis have been linearly normalized to 35 wt-% for comparison purposes. • All specimens other than the OEM pellets were manufactured using the D-LFT-ILC or D-LFT-EMC process. • Densities: PP — 0.946 g/cm 3 , PA6 — 1.13 g/cm 3 , PA6.6 — 1.14 g/cm 3 , carbon 1.81 g/cm 3 , E-glass — 2.55 g/cm 3 .