**3. Manufacturing of composites**

spondingly. Because of high values of variation coefficients of these parameters, the above differences are non-essential. The silane modification results in increase in the value of degree of crystallinity of cellulose sub-microfibres by about 6% apart from the conditions of silane modification. The degree of crystallinity of sub-microfibres without the silane modification is

**Figure 4.** SEM images of cellulose sub-microfibres from straw (straw of retted fibre flax, SRFF, straw of oil flax, SOF,

**Mean value (μm)** 

LI-1 Without 11.36 81.0 146.55 73.7 79.0 LI-2 Silane in ethanol 12.28 37.5 117.21 54.3 85.1 LI-3 Silane in ethanol+water 13.46 35.7 138.83 61.4 85.3

SRFF-1 Without 5.62 48.40 70.00 53.16 68.3 SRFF-2 Silane in acetone 1.64 56.7 16.1 55.1 59.4 SOF-1 Without 11.09 46.80 89.07 61.65 63.2 SOF-2 Silane in acetone 8.94 55.06 46.35 35.77 61.3 HS-1 Without 6.33 40.13 55.24 64.30 65.8 HS-2 Silane in acetone 2.43 36.67 19.64 33.11 65.3

**Fineness Length Degree of**

**CV (%) Mean value (μm)**

**crystallinity**

**CV (%) %**

79% and after the silane modification takes the value above 85%.

222 Composites from Renewable and Sustainable Materials

**Silane modification of sub-microfibres**

Cellulose sub-microfibres from waste flax fibres

**Table 1.** Characteristics of cellulose sub-microfibres [21].

Cellulose sub-microfibres from straw

hemp straw, HS).

**Symbol of submicrofibres**

> Thermoplastic composites were obtained from the multilayer structures in a hydraulic press machine using a water-cooling system from Hydromega (Poland). The press conditions for all multilayer structures were the same, i.e., temperature 170–175°C, time 5 min and pressure 0.275

MPa. The multilayer structure was wrapped with Teflon foil to prevent molten polymer propagation during the pressing process.

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 and the top of multilayer structure was covered by 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 fibres 'CO'.

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 parameters: type of needles – 15 × 18 × 40 × 31 /2 RB (Groz-Beckert®), number of needle punches —40/cm2 , depth of needle punching—12 mm [16].
