Short-fiber thermoplastic composites

Short-fiber thermoplastic composites are typically injection molded, which allows rapid, high-volume, and economical production but requires expensive tooling. The fiber length and volume fraction are limited by this method, and fiber orientation and distribution are difficult to control. 

Lewis-Nielsen equation An equation derived from the theory of mixtures that provides an estimate of the modulus of a short-fiber, thermoplastic composite. It is given below. 

Nando, G.B. and Gupta, B.R., Short fibre-thermoplastic elastomer composites, in Short Fiber—Polymer Composites, De, S.K. and White, J.R. (Eds.), Woodhead Publishing, Cambridge, 1996, Chapter 4. 

Friedrich K. (1985). Microstructural efficiency and fracture toughness of short fiber/thermoplastic matrix composites. Composites Sci. Technol. 22, 43-74. 

Mandell J.F., Huang, D.D. and McGarry F.3. (1982). Crack propagation modes in injection molded fiber reinforced thermoplastics. In Short Fiber Reinforced Composite Materials, ASTM STP 772 (B.A. Sanders ed.), ASTM, Philadelphia, PA, pp. 3-32. 

The properties of thermoplastic composites containing fibers as fillers are dependent on a number of parameters, which include the properties of the matrix material, the size and aspect ratio of the fibers, dispersion of the fibers and the interface. In development of these composites, two important issues need to be addressed, namely, the incompatibility between the natural fibers and polymer matrix, and the tendency of the fibers to form aggregates [67]. Additionally, the composites exhibit poor dimensional stability due to moisture absorption. The orientation of the fibers is also important. In short-fiber reinforced composites, the orientation of the fibers is usually random and therefore the properties of such composites are not as superior as those containing continuous fibers. Optimization of processing conditions and use of coupling agents/compatibilizers and treatment of fibers can enhance the properties of these composites. 

In an injection-molded short-fiber-reinforced thermoplastic, there is a distribution of fiber lengths. Not all fibers are oriented in one direction. Taking these factors into consideration, Bowyer and Bader (86) proposed the following equation to predict the theoretical strength of the short-fiber-reinforced composite ... 

Figure 3.429. Schematic of factors influencing the mechanical performance of short fiber/ thermoplastic matix composites [1253],...

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

Fig. 6.8. Fracture toughness, K, of short glass fiber-thermoplastics injection molded composites as a function of weight fraction of fiber, fVr. (O) and (A) polyethylene terephthalate (PET) matrix ( ) and (A) polycarbonate (PC) matrix. Notches made transverse (O, ) and parallel (A, A) to the mold fill direction,...

Fig. 6.9. Normalized fracture toughness, (Kc - AKQ)/K. of short glass fiber-thermoplastics injection molded composites as a function of reinforcing effectiveness parameter, ft (O) polyetheretherketone (PEEK) matrix (K = 6.5 MPa m) (A) polytetrafluoroethylene (PTFE) matrix (K = 1.9 MPaym).

Fig. 6.10. Schematics of the dependence of total fracture toughness, on fiber volume fraction of short fiber reinforced thermoplastic composites at different loading rates (a) static loading (b) dynamic...

Friedrich, K. and Karger-Kocsis, J. (1989). Unfilled and short fiber reinforced semi-crystalline thermoplastics. In Fractography and Failure Mechanisms of Polymers and Composites, (A.C. Roulin-Moloney ed.), Elsevier Appl. Science, London, pp. 437-494. 

Lauke B., Schultrich B. and Barthel R, (1985). Contribution to the micromechanical interpretation of fracture work of short-fiber reinforced thermoplastics. Composites Sci. Technol. 23, 21-35. 

Lauke B. and Schultrich B. (1986b). Fracture toughness of short fiber reinforced thermoplastics. Composites. Sci. Technol. 26, 37-57. 

Ramsleiner F. and Theysohn R. (1979). Tensile and impact strength of uni-directional short fiber reinforced thermoplastics. Composites 10, 111-119. 

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