Melt Spinning of PLA

F ure 5.10 Spiiming devices spin drawing process, high speed spinning process) [16] 

In dieir another report, PLA with different Z -lactide contents, taticities, molecular mass and molecular mass distribution was used in high-speed melt-spinning process [18], The spinnability of PLA with broad mass distribution was extremely restricted. Hie crystallinity of fibers which was influenced by D content and the extent of orientation-initiated crystallization had a decisive influence on the tensile properties Of the investigated PLA fibers. 

It is well known [21] that die melting temperature and the degree of crystallinity of PLA polymerized fi-om -lactide can be controlled by the thermoplastic processing and by the insertion of D-lactic acid units and other monomer units [22] 

2 Effect of Spinning Parameters on the Structure and Properties of PLA Fibers 

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FIGURE 29.3 Relationship of yarn properties (tensile strength, Young s modulus, and ultimate elongation) and take-up speed for melt spinning of PLA. 

PLA and PHB may be processed because of their thermoplastic properties in the usual thermoplastic processing systems by using extrusion, injection molding, melt spinning, blowing film, and melt-blown techniques. 

For this comparison, a melt-spinning process was chosen. Each special thermoplastic process influences the structure and thus the properties of the obtained polymer samples differently. This is particularly pronounced for fibers, since especially melt spinning is a process which makes extremely high demands on the deformation ability of the polymer melts at high deformation speeds. Particularly the tensile stress within the fiber formation zone is a very important factor to reach a high orientation of the macromolecules along the fiber axis and a stress-induced crystallization. This crystallization should be discussed in relation to PLA and PHB multifilaments, and at the same time the general property spectrum of these polymers should be represented. 

PLA Fambri et al. [27] compiled a list of present literature data on PLA fibers, which were spun under quite different technological conditions, dry spinning, solution spinning, melt spinning, and spin drawing. 

It is an aliphatic polyester derived from renewable resources, such as com starch, tapioca roots, chips or starch, or sugarcane. Polylactic acid or polylactide (PLA) can withstand temperatures up to 110 °C [69]. PLA is soluble in chlorinated solvents, hot benzene, tetrahydrofuran, and dioxane [70]. It can be processed like other thermoplastics into fiber (for example, using conventional melt spinning processes) and film. Due to the chiral nature of lactic acid, several distinct forms of polylactide exist ... 

The mechanical propoties of PLA-related polymers were recently reviewed by Sodergard and Stolt [7], who showed, among other features, that the PLLA fibre modulus can be increased from 7-9 GPa to 10-16 GPa by going from melt to solution spinning. The mechanical behaviour can also be modified by preparing suitable copolymo-s, as in the case of the use of CL, which, with its soft segments, induces a decrease in modulus and an increase in the elongation at break, respectively. 

Although PLA fibres are used in different textile applications as, for example, non-woven textile for clothes, they achieved their first commercial success as resorbable sutures. One of the first commercially available fibre-formed bioresorbable medical products is based on copolymers of GA in combination with L-lactide (Vicryl) [67]. Fibres can be produced both by solvent and by melt-spinning processes and drawn under different conditions to orient the macro molecules [7]. 

Figure 9.6 SEM micrographs of biocompati- PLA in the blend 20wt%, (b) PCL of 20 wt%, ble biodegradable polyesters after their melt (c) PHB after melt spinning from a PVA/PHB blending with PVA with extrusion, cold draw- blend 90/10 by wt%, and (d) the same at ing, and extraction with water, (a) Amount of higher magnification.

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