The most popular bio based fiber reinforced polyla

2022-07-26
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Bio based fiber reinforced polylactic acid material

due to the high-efficiency reinforcing effect of acetate fiber in bio based plastics, acetate fiber is in the revival stage. Considering the unique structure of acetate fiber, they can simultaneously improve the performance of materials, such as newly developed polylactic acid compounds. In this way, a specially customized all bio based polylactic acid material is produced, which combines high strength, rigidity and excellent impact strength

since the 1960s, acetate has been mainly used as reinforcement for high-speed tires and later explosion-proof tires. These acetate materials are called viscose tire cord yarns, which strengthen the tire ply in the form of a single layer of fabric

the first attempt to integrate short acetate fiber into thermoplastic matrix can be traced back to 1998. In 2002, an article in Kunststoffe International Magazine showed that viscose reinforced polypropylene compounds have the potential to be used in automotive interior parts, such as automotive door panels. Bio based organic acetate fiber not only improves the mechanical properties of polypropylene matrix, but also provides blending manufacturers and users with advantages superior to the traditional glass fiber reinforced materials with composite particles, including weight reduction, lower wear resistance requirements of mixing equipment, renewability and energy recovery

acetate fiber is used as reinforcing agent

bio based materials, including plastics based on renewable resources, which are very popular with manufacturers at present. One reason is the increasing demand of consumers for eco-friendly and sustainable products. The other reason is that the availability of oil is increasingly restricted, so it is very important to reduce the dependence on oil in the future. In particular, people are increasingly interested in polylactic acid (PLA), which is regarded as the future bioplastics. However, the use of PLA in industry is still limited by its low impact strength

this article shows that 38 technical achievements, such as the process design of power increasing crank crank arm with acetate fiber for polylactic acid, have been transformed in Yucheng, and the reinforcement with polypropylene will lead to the simultaneous improvement of three properties: strength, rigidity and impact resistance. In this process, the compound maintains the whole biological base. The article also introduces a new generation of acetate fiber reinforced polylactic acid compounds, which have very high impact strength. The significant improvement of this property is entirely due to the change of fiber matrix interaction. There is no doubt that this can be adjusted by adding appropriate additives in the mixing process

production and testing of compounds

the base material used is 4042d polylactic acid, which can be used in film production after optimization. The molecular weight Mw is 170, 000g/mol, the content of D-lactic acid is 8%, the melt melt melt index (MFI) is 18g/10min (2.16kg, 210 ℃), and the density is 1.25g/cm3 (manufacturer: nature works). RT 700 high toughness acetate fiber (manufacturer: cordenka company) is selected as the reinforcing material. These high-performance acetate fibers are usually used as the cord of viscose tires in high-speed tires. They have very high strength (885mpa), rigidity (19.5gpa) and elongation at break (12.5%), and the single fiber diameter is relatively consistent and stable at 12 μ M. The mechanical strength values quoted here come from our own tensile tests on single fibers. For impact modification of polylactic acid compounds, random polypropylene maleic anhydride graft copolymer (MAPP; manufacturer: DuPont) with weight percentage of 3% and grafting rate of 1.4% was used to reduce the adhesion of fiber matrix (as follows)

polylactic acid and 20% acetic acid continuous filament were mixed at 170 ℃, and the rheocord 9000 ptw25 reverse rotating twin screw extruder of HAQ company in Germany was used for continuous double pultrusion

then the pellets are processed on an injection molding machine (Arburg allrounder 270m of Arburg company in Germany) according to DIN EN ISO standards. The processing temperature of standard test samples (dumbbell shaped splines and blocks) is 170 ℃ to 180 ℃, and the injection pressure is between 1000 and 1200bar. According to DIN EN iso527 and 178 standards, the mechanical properties of the sample under quasi-static stress, such as tensile strength, are determined on the zwick1445 tensile testing machine of Zwick company in Germany( σ M then the test cannot be carried out ax), tensile modulus (etens), elongation at break( ξ B) , and flexural modulus (eflex). The impact resistance, such as the impact strength (AC) and notch impact strength (ACN) of simply supported beams, the absorbed penetration energy (EP), the maximum generating force (FM) and the ratio of energy loss to stored energy (material damping, Δ) The pendulum impact tester manufactured by Wolfgang ohst and the drop hammer impact tester manufactured by ceast are used according to DIN EN iso179 and. All test samples shall be placed in the climate test chamber at 23 ℃ and 50% relative humidity for a specific period of time

first successful attempt at

first generation polylactic acid compounds. The first attempt to mix polylactic acid and acetic acid fiber has achieved great success, and the processing and formula optimization have not incurred a lot of costs. The fracture surface of such a compound in Figure 1 clearly shows that although each individual part has extremely different hydrophilic properties, it can still produce a polymer fiber material with a uniform structure with sufficient adhesion. Only adding 20% acetic acid fiber by weight can significantly improve the performance level of PLA. Fig. 2 shows that compared with unreinforced PLA, the strength of the compound is increased by 40% (up to 104mpa), and the tensile and flexural modulus are increased by 50% and 65% (up to 4.3 and 5.0gpa) respectively. A particularly surprising result is that the energy absorption capacity of the compound under impact stress (Fig. 3) and osmotic stress is significantly improved (Fig. 4), while the impact strength of notched and non notched simply supported beams is three times higher than that of unreinforced PLA at room temperature and two times higher at -18 ℃. Absorption permeation energy (EP) reaches three times, material damping( Δ) From 0 to 0.2

optimize fiber matrix adhesion

second generation polylactic acid compounds. In the further development of polylactic acid compounds, the initial focus is to improve the fiber matrix adhesion. Since there is no commercially available adhesion enhancer specifically for this material, we have taken our own approach to solve this problem. Adding 1% hexamethylene diisocyanate by weight in the mixing process can obtain very good fiber matrix adhesion. This can also be seen by using scanning electron microscope (SEM) to analyze the morphology of the fracture surface of the compound (Fig. 5). The test results have been published in the figure, but the increase of tensile strength by 15% and the decrease of impact strength by 15% did not meet the expectations

in contrast, adding 3% by weight of MAPP to reduce the fiber matrix adhesion can produce high impact compounds. According to the mechanism described by Felix and gatenholm, hydrophobic MAPP is irreversibly bonded to the fiber surface and completely coated on the fiber surface during the melting mixing process. Therefore, the interaction between hydrophobic acetate fiber and polylactic acid matrix via dipole and/or hydrogen bridge bonding no longer occurs. When the test sample is subjected to elastic stress, the matrix will absorb a large amount of energy and peel off with the fiber from the experimental model, which can be divided into four types: A-type machine, B-type machine, C-type machine and D-type machine, and the fiber under strong friction will be pulled out. As can be seen from Fig. 5, in addition to other reasons, sometimes extremely long drawn fibers are also responsible for enhanced impact energy absorption

The rigidity of the

compound basically did not change, but remained at a high level, while the strength only decreased slightly (Fig. 2), and all measured impact strength values were significantly increased as shown in Fig. 3 and Fig. 4. The impact strength value of 20% by weight of fiber content measured by non notched test sample is 95kj/m2, while that measured by notched sample is 26 kj/m2 (Fig. 3). This represents a five to ten fold increase over unreinforced polylactic acid and a two/three fold increase over unmodified compounds

conclusion

even a small amount of high tenacity acetate fiber (20% by weight) in PLA matrix can bring significant and simultaneous reinforcement effect. The brittleness of PLA can be overcome by reinforcing with acetate fiber without adding plasticizer in brittle or flexible plastics. The interaction between fiber and matrix at the interface has a decisive effect on the properties of the compound. (end)

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