Wgscb Wgscb

PSCBGU PWFGU

WG PVA SCB WF Gly

Urea

Note: WG = waste gelatin; SCB = sugarcane bagasse; WF = wheat flour; Gly = glycerol.

Previous investigation on the applications of PVA-water solutions to soil outlined that, when sprayed on the soil surface, the solutions penetrated about 0.5 cm into the soil. When a PVA solution 5% by weight was applied, the soil appeared to be covered with a thin, wet, transparent, but poorly aggregated layer. With a PVA solution 10% by weight was applied, a thin plastic layer was formed on the soil surface; soil formed a very fragile crust, about 0.5 cm high, together with the polymer.73

The results of sprayed-film experiments showed that PVA and WG water suspensions were easy to spray; mixture-soil aggregates lasted for more than 3 weeks on the soil; and the soil appeared to be conditioned and in a better state when compared with the control sample. Formulations containing SCB conferred a marked brown color to the soil. The presence of WG, WF, and SCB enhanced PVA longevity on the soil, thus guaranteeing the resultant soil-structuring effect. In consideration of these positive effects, the hydro-biomulching formulations were further tested in the presence of seeds and plants.

Water suspensions based on PVA (P) and wheat flour (WF) and on PVA and sugar cane bagasse (SCB) were prepared at 15% by weight. Both suspensions also contained glycerol (G) and urea (U) (PWFGU and PSCBGU, respectively, in Table 5.4). To evaluate a possible influence of the amount of applied material, each suspension was applied at two different doses: 1 and 3 l/m2. Eighty seeds of lettuce (Lactuca sativa) were planted in a 25-cm diameter pot. Selected water suspensions were sprayed on the soil surface. After 50 days, the average number (three replicates) of germinated seeds was recorded (Table 5.5).

In all cases, a homogeneous coverage of the pots was obtained. A strong negative effect on germination was detected, especially in pots treated with the WF-based formulations, which formed a hard crust on top of the soil, thus effectively inhibiting emergence through the film by the lettuce sprouts. Furthermore, possible direct contact of seeds with the composite formulation (lettuce seeds were buried only 0.5 cm deep) might have interfered with seed transpiration due to the viscosity of the water suspension. Also the large amount of urea applied could have had a negative effect on seed germination.

To verify whether the mixtures had a negative effect on growing plants or only on seed germination, the following test was set. Lettuce seedlings were transplanted into 14-cm-diam. pots (one plant in each pot), and then the soil was sprayed with the same formulations as above. For comparison, another test was prepared by directly spraying the liquid mixtures in the soil and then planting the seedling lettuce.

TABLE 5.5

Results of Lettuce Germination in Pots

Dose Germination

Control 0 63

PWFGU 1 8

PWFGU 3 0

PSCBGU 1 33

PSCBGU 3 3

TABLE 5.6

Hydro-Biomulching Formulation Based on PVA and Lignocellulosic Filler

TABLE 5.6

Hydro-Biomulching Formulation Based on PVA and Lignocellulosic Filler

PVA

Organic

Filler

Water

Treatment

(g/m2)

Type

g/m2

(g/m2)

PSCB

20

SCB

40

340

PWF

20

WF

40

340

PWS

20

WS

500

380

PSD

20

SD

500

380

Note: SCB = sugarcane bagasse; WF = wheat flour; WS = wheat straw (milled); SD = sawdust.

Note: SCB = sugarcane bagasse; WF = wheat flour; WS = wheat straw (milled); SD = sawdust.

This procedure was carried out to promote a direct contact of the formulations with lettuce roots. With both these procedures no toxic effect was observed, and lettuce plants appeared to grow at a faster rate in the conditioned pots.

A further appraisal of the potential effect of hydro-biomulching based on PVA and natural fillers was conducted during a field trial at the University of Pisa in summer between June and September. Two conventional mulching materials — polyethylene film (PE) (70 g/m2) and raw straw mulching (SM) (100 g/m2) — were compared with the innovative PVA-based hydro-biomulching formulations represented by PSCBGU, PWFGU, and a PVA-water solution used as tackifiers on coarsely milled wheat straw (WS) with an average size of 20 mm, and on sawdust (SD), a commercial product from softwood sawmill (Table 5.6).

Sawdust and wheat straw were spread directly on the soil at a level of 500 g/m2 prior to the spray application of the PVA solution. Corn (Zea mays) and lettuce (Lactuca sativa) were chosen to test the agronomic effect of the mulching treatments on seeded and transplanted crops. For each plot, three corn plants were established by sowing and three plants of lettuce were established by transplanting seedlings. Each trial was carried out on nine replicates. All the lettuce plants were harvested 50 days after transplanting, and fresh weight was measured and reported as an average weight (Figure 5.4).

Images Zea Mays Seedlings Plants
FIGURE 5.4 Average fresh weight of lettuce plants 50 days after transplanting.
Images Zea Mays Seedlings Plants
FIGURE 5.5 Average dry weight of corn plants after 100 days from seedling.

For lettuce, all of the PVA-based fluid mulching treatments produced results that were comparable with PE and significantly different from those obtained with the control and the semidry mulching (PWS and PSD). For corn, all of the fluid mulching treatments performed better than the untreated soil, although only the PSCB formulation approached the efficiency of the PSCB formulation (Figure 5.5).

Differences in the soil structure were evident from visual field observations at the end of the experiment. Figure 5.6 refers to the soil surface at the end of the trial in plots that had received PVA/SCB, PVA/WF, and the control not submitted to any mulching treatment. Soil aggregates (1 to 2 cm) were still present in treated soil, while they were completely disrupted in the control plot, thus confirming the positive effect on soil structure preservation previously observed in laboratory-scale tests.

Hydrofield
FIGURE 5.6 Soil appearance at the end of the hydro field trial: a) control, b) PVA/SCB, c) PVA/WF.

5.2.2 Films and Laminates Based on PVA and Natural Fillers from Agroindustrial Waste

Hybrid composites were prepared by using PVA of Mn 100 to 146 kDa and a 96% degree of hydrolysis. Natural fillers were represented by cellulosic materials from three different sources: sugarcane bagasse (SCB), orange (OR), and apple peel (AP), which were the remains of fruit residue after juice extraction.404647 All cellulosic materials were milled and sieved to obtain particles sizes <0.188 mm.

Unmodified commercial-grade corn/starch with approximately 30% amylose and 70% amylopectin (U.S.) was added in some formulations to replace as much PVA as possible without compromising the film properties. Films were prepared by casting of water suspensions, 10% by weight. While maintaining a 1/1 PVA/fiber ratio, glycerol, urea, and starch were introduced in the formulation as reported in Table 5.7. Addition of glycerol and urea softened the films (Figure 5.7), as both glycerol and urea are known to act as a plasticizer for PVA in PVA/starch-based films.75-77

Effect of starch addition on mechanical properties is reported in Figure 5.8. In PVA/OR blends, starch addition caused significant reduction in elongation a break, with somewhat moderate variation in ultimate tensile strength (UTS). Excellent film-forming properties and flexibility were observed in films, even when starch concentration in formulations exceeded 25%. In PVA/SCB blends, elongation at break (EB) was mostly unaffected by starch content, while UTS increased with starch addition; thus the introduction of starch increased cohesiveness of PVA/SCB films. In contrast, in PVA/AP blends, addition of starch increased the presence of defects, and small holes were detected in the films, thus indicating a loss in mechanical properties due to increased starch content.

Given the positive results observed, particularly for the hybrid composites based on OR fibers prepared by casting, further tests were performed by compression

TABLE 5.7

Composition of the Composite Films Prepared by Casting from Water Suspensions of PVA and Natural Fillers (OR, SC, AP)

TABLE 5.7

Composition of the Composite Films Prepared by Casting from Water Suspensions of PVA and Natural Fillers (OR, SC, AP)

PVA

Natural Fiber

Glycerol

Urea

Starch

Sample

(%)

(%)

(%)

(%)

(%)

POR50

50.0

50.0

0.0

0.0

0.0

PORGU1

40.0

40.0

10.0

10.0

0.0

PORGU2

33.3

33.3

16.6

16.6

0.0

PORGU3

25.0

25.0

25.0

25.0

0.0

PORStl

31.0

31.0

15.0

15.0

8.0

PORSt2

28.6

28.6

14.3

14.3

14.3

PORSt3

25.0

25.0

12.5

12.5

25.0

Note: POR series based on orange peel (OR) as filler; PSC series based on sugarcane bagasse (SC) as filler; PAP series based on apple peel (AP) as filler. G = glycerol; U = urea; St = starch.

Note: POR series based on orange peel (OR) as filler; PSC series based on sugarcane bagasse (SC) as filler; PAP series based on apple peel (AP) as filler. G = glycerol; U = urea; St = starch.

O 100

20 33

Glycerol/Urea (%)

qj 5 773

20 33

Glycerol/Urea (%)

Renewable Resources Images

20 33

Glycerol/Urea (%)

20 33

Glycerol/Urea (%)

20 33

Glycerol/Urea (%)

FIGURE 5.7 Mechanical properties as a function of plasticizers content; a) elongation at break, b) ultimate tensile strength, c) Young's modulus.

20 33

Glycerol/Urea (%)

FIGURE 5.7 Mechanical properties as a function of plasticizers content; a) elongation at break, b) ultimate tensile strength, c) Young's modulus.

Ultimate Compressive Strength Table
0 8 14 25
Young Modulus Table
FIGURE 5.8 Mechanical properties as a function of starch content; a) elongation at break, b) ultimate tensile strength, c) Young's modulus.

TABLE 5.8

Composition of Biobased Mixtures in Compression Molding

TABLE 5.8

Composition of Biobased Mixtures in Compression Molding

PVA

Fibers

Starch

Glycerol

Samples a

(%)

Type

(%)

(%)

(%)

PStG

44

28

28

PORG

44

OR

28

28

PStSCB, PstOR, PStAP

34

SC, OR, AP

22

22

22

PStORU

25

OR

25

25

12.5 b

a P = poly(vinyl alcohol); St = starch; G = glycerol; SCB = sugar cane bagasse; OR = orange peel; AP = apple peel; U = urea. b Containing 12.5 % of urea.

a P = poly(vinyl alcohol); St = starch; G = glycerol; SCB = sugar cane bagasse; OR = orange peel; AP = apple peel; U = urea. b Containing 12.5 % of urea.

molding. Laminates based on PVA and natural fibers were prepared with compositions as reported in Table 5.8. About 20% water was added to each composition before processing.11 Mechanical properties of the prepared laminates are shown in Figure 5.9.

OR was selected for the first attempts aimed at producing composites by compression molding, since films based on PVA and OR proved to be homogeneous, flexible, and more cohesive than composites based on PVA and SCB or AP. Thus the substitution of starch (PStG) with orange waste (PORG) in the hybrid composite based on PVA and glycerol presented a modest variation in mechanical properties. Comparison of PORG with PStOR mechanical properties suggested that the introduction of starch in the formulation moderately decreased mechanical properties.

Composites prepared with AP (PStAP) presented EB values (61%) similar to those of the composites prepared with OR (PStOR), but higher UTS (9 MPa) and

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