Japan’s Ube develops composite PP/PE filament for automotive lightweighting

A composite filament consisting of a polypropylene (PP) core and low melting point linear low-density polyethylene (LLDPE) outer layer is employed in a new thermoformable textile called Simtex from Ube Exsymo (Tokyo).

Fabric woven from the filament can be thermoformed usually in multiple plies, to form rigid components such as automobile ceiling liners and travel bags. During the thermoforming process, the LLDPE resin alone melts to form a matrix that encapsulates the PP fibers.

The fiber is supplied in 1000–3000 decitex (dtex; mass in grams per 10,000 meters) rolls. Strength of 10 cN/dtex is double that of conventional PP fiber while tensile strength (Young’s modulus) of around 95 cN/dtex is triple that of PP fiber.

A test component thermoformed from four plies of 250 g/m² of Simtex fabric at 140°C and 1 MPa pressure yielded a 1.3-mm-thick part with density of 0.9 whose tensile strength was 200 MPa, tensile modulus 3500 MPa, flexural strength 54 MPa, and flexural modulus 2500 MPa.

Sister company Ube Material Industries, meanwhile, is promoting a fibrous magnesium oxysulfate filler, MOS-HIGE whisker, for use as a reinforcement in PP compounds that also functions to improve flowability. A talc-filled PP compound consisting of 76% PP, 7% talc, 7% MOS-HIGE, and 10% elastomer exhibits a flexural modulus of 2600 MPa and a melt flow ratio (MFR) of 17.7 g/10min. Density is also reduced to 1.00. This compares with a flexural modulus of 2400 MPa, an MFR of 8.7 g/10min, and a density of 1.05 for a PP compound consisting of 70% base resin, 20% talc and 10% elastomer.

MOS-HIGE before compounding consists of fibers of mean length of 10 μm and mean diameter of 0.5 μm (aspect ratio 20). After compounding with PP, the MOS-HIGE whiskers do not break to any great extent, becoming fibers of mean length of 5 μm and mean diameter of 0.5 μm (aspect ratio 10).

Ube Material Industries has also discovered a means of improving impact strength while retaining flexural modulus. Addition of nanosilica in a ratio of 0.01–0.2 parts per hundred was found to be the optimum range for maximizing both Izod impact strength and flexural modulus.

Another positive trait of MOS-HIGE is a superior surface finish compared with glass fiber reinforced compounds. At a 7.4% loading, surface roughness of a PP compound containing MOS-HIGE is more than three times superior to that of a glass-filled compound, and in addition superior to that of a 7.4% talc-filled compound. Surface finish is almost seven time better at a loading of 12.1%.

Ube Material Industries currently has an annual production capacity of 3,000 tonnes of MOS-HIGE at its plant in Yamaguchi Prefecture, Japan, having already expanded production facilities twice, in 2012 and 2015. With demand for MOS-HIGE whisker expected to continue growing, and with its commitment to better serving the local procurement needs of plastic compounders outside of Japan, Ube Material Industries established a local subsidiary in Thailand, which is a center for automotive production in Southeast Asia, that will start manufacturing MOS-HIGE in 2019.