(b) straws:

Three kinds of straw: grinded sunflower straw (SS), grinded corn straw (CS) and random cut wheat straw (WS) were cultivated and prepared by University of Agriculture in Cracow, Poland. The reinforcing materials are presented in **Figure 2**.

**Figure 1.** Photographs of the waste natural fibres reinforcement.

**Figure 2.** Photographs of the straw reinforcement.

Each kind of reinforcing material is characterized by diversified length and width. The length results from the random cutting process. The width is dependent on the native fibre or straw stem. Moreover, in the case of sunflower straw, two kinds of the particles can be distinguished, oblong particles coming from a hard envelope and more rounded particles coming from the soft inner parts. The corn straw particles are similar to sunflower ones but with smaller part of soft almost round particles. The wheat straw particles have the hollow channels.

(c) cellulose ultra-short/ultra-fine fibres obtained from:



as a result of different processes depending on raw materials.

(b) straws:

Three kinds of straw: grinded sunflower straw (SS), grinded corn straw (CS) and random cut wheat straw (WS) were cultivated and prepared by University of Agriculture in Cracow,

Each kind of reinforcing material is characterized by diversified length and width. The length results from the random cutting process. The width is dependent on the native fibre or straw stem. Moreover, in the case of sunflower straw, two kinds of the particles can be distinguished, oblong particles coming from a hard envelope and more rounded particles coming from the soft inner parts. The corn straw particles are similar to sunflower ones but with smaller part

of soft almost round particles. The wheat straw particles have the hollow channels.

Poland. The reinforcing materials are presented in **Figure 2**.

220 Composites from Renewable and Sustainable Materials

**Figure 1.** Photographs of the waste natural fibres reinforcement.

**Figure 2.** Photographs of the straw reinforcement.

(c) cellulose ultra-short/ultra-fine fibres obtained from:

In order to obtain cellulose ultra-short/ultra-fine fibres, the flax fibres or straw were cut to the pieces of several centimetres and treated by enzyme preparation. The enzymatic treatment causes the decrease in length and fineness of starting materials. The fibres obtained, called as sub-microfibres, were dried at an ambient temperature and ground in a disk mill and then treated or not by 3-aminopropyltriethoxysilane STRUKTOL® SCA 1100 (Struktol Company of America, USA). That modification usually is used to increase adhesion of fibres to a hydrophobic matrix. In this case, silane modification was used also to prevent fibres connection in the polymer matrix. In the case of sub-microfibres obtained from waste flax fibres, two kinds of silane modifications were used, i.e., by 10 wt% solution of 3-aminopropyltriethoxysilane in ethanol or by 10 wt% solution of 3-aminopropyltriethoxysilane in mixture of ethanol and water to obtain additional activation. The surface of sub-microfibres obtained from straw was modified by 10 wt% solution of 3-aminopropyltriethoxysilane in acetone. That modification causes an agglomeration of sub-microfibres.

After silane modification, the cellulose sub-microfibres were ground in a disk mill. The submicrofibres obtained from waste flax fibres and straw are presented in **Figures 3** and **4**, respectively.

**Figure 3.** SEM images of cellulose sub-microfibres from waste flax fibres.

Characteristics of all cellulose sub-microfibres, with and without silane modification, are presented in **Table 1**.

The silane modification of the cellulose sub-microfibres obtained from waste flax fibres has not influence their morphological properties. The fineness of the sub-microfibres without modification is 11.36 μm and the length is 146.55 μm. The fineness of the sub-microfibres after the silane modification in solution of silane in ethanol is 12.28 μm and the fineness of the submicrofibres after modification in solution of silane in mixture of ethanol and water is 13.46 μm. The length of the sub-microfibres after modification is 117.21 μm and 138.83 μm, correspondingly. 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 79% and after the silane modification takes the value above 85%.

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


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

The silane modification of the cellulose sub-microfibres obtained from different kinds of straw causes the reduction of fibre dimensions. The fineness of the sub-microfibres from the SRFF straw without silane modification is 5.62 μm, from the SOF straw it is 11.09 μm and from HS it is 6.33μm. The fineness of the sub-microfibres from SRFF straw after silane modification is 1.64 μm, from SOF straw it is 8.94 μm and from HS it is 2.43 μm. The length of the submicrofibres after the enzymatic treatment is 70.00 μm for SRFF, 89.07 μm for SOF, and 55.24 μm for SOF straw. The length of the sub-microfibres from straw after silane modification is 16.1 μm for SRFF straw, 46.35 μm for SOF straw and 19.64 μm for HS straw. The values of variation coefficients of these parameters are very high. The silane modification has not significant influence on the degree of crystallinity of the cellulose sub-microfibres obtained from SOF and HS straws. For these sub-microfibres, the values of the degree of crystallinity change from 63.2 to 61.3% for SOF straw and from 65.8 to 65.3% for HS straw. In the case of sub-microfibres obtained from SRFF straw, the values of the degree of crystallinity are lower by 9% after silane modification.

The dimensions of the cellulose sub-microfibres obtained from flax fibres can be further reduced during the mechanical treatment in an aqueous suspension by means of a homogenizer. The length decreases to about 6 μm and diameter to about 300 nm. These fibres, **Figure 5**, referred to as sub-micro/nanofibres, were not dried to prevent their agglomeration.

**Figure 5.** SEM image of the sub-micro/nanofibres from flax fibres [16].
