**5. Results**

MPa. The multilayer structure was wrapped with Teflon foil to prevent molten polymer

It was assumed to obtain composite samples with similar thicknesses to allow for assessment of the effect of the reinforcement type. Each multilayer structure was composed of several layers of nonwovens either separated alternately or not by layers of grinded straw or cellulose ultra-short/ultra-fine fibres. The appropriate mass of straw/cellulose ultra-short/ultra-fine fibres was divided in portions, which were put uniformly onto consecutive layers of nonwoven

The needle-punched nonwovens were manufactured from matrix fibres 'PLA (100%)' or from a blend consisting of matrix fibres 'PLA' and reinforcing waste flax fibres 'LI' or waste cotton

In order to manufacture needle-punched nonwovens the fleeces with a cross-system of fibre arrangement were obtained on the roller card. Needle punching of the fleece layers was carried out on an Asselin needle punching machine (France), with the following technological

The thickness of composites was determined according to the standard procedure ISO 9073-2:1995 and their apparent density was determined as the ratio of mass to volume of samples. The mechanical properties of composites were estimated in unidirectional tensile test by means of testing machine type 3119-410 (Instron, UK) according to the standard ISO 527-4:1997. The sound absorption coefficient was determined according to the standard procedure ISO 10534-2:1998 within the frequency range of 500–6400 Hz. A small size impedance tube (Kundt tube) type 4206 (Brüel&Kjaer, Denmark) was used (**Figure 6**). The diameter

/2 RB (Groz-Beckert®), number of needle punches

propagation during the pressing process.

224 Composites from Renewable and Sustainable Materials

parameters: type of needles – 15 × 18 × 40 × 31

of the investigated samples was equal to 29 mm.

**Figure 6.** The Kund device for acoustic measurements.

fibres 'CO'.

—40/cm2

**4. Methods**

and the top of multilayer structure was covered by nonwoven.

, depth of needle punching—12 mm [16].

The values of mass per square meter were similar for all nonwovens, i.e., in the range of 115– 120 g/m2 . The composites obtained were rigid with a small thickness of a few millimetres, 'green', and designed among others from cheap components coming from renewable resources. Each composite was manufactured from the system consisting of 80 wt% of nonwoven (PLA (100%) or PLA/LI (80/20%) or PLA/CO (90/10%)) and 20 wt% of straw or cellulose ultrashort/ultra-fine fibres.
