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Summary: Blends and composites based on environmentally degradable-ecocompatible synthetic and natural polymeric materials and fillers of natural origin have been prepared and processed under different conditions. Poly (vinyl alcohol) (PVA) was used as the synthetic polymer of choice by virtue of its capability to be processed from water solution or suspension as well as from the melt by blow extrusion and injection molding. Starch and gelatin were taken as the polymeric materials from renewable resources. The fillers were all of natural origin, as waste from food and agro-industry consisted of sugar cane bagasse (SCB), wheat flour (WF), orange peels (OR), apple peels (AP), corn fibres (CF), saw dust (SD) and wheat straw (WS). All the natural or hybrid formulations were intended to be utilized for the production of:
and mechanical properties and tested with different methodology for their propensity to environmental degradation and biodegradation as ultimate stage of theirservice life. A relationship between chemical composition and mechanical properties and propensity to biodegradation has been discussed in a few representative cases.
a) Environmentally degradable mulching films (hydrobiomulching) displaying, in some cases, self-fertilizing characteristics by in situ spraying of water solutions or suspensions; b) Laminates and containers to be used in agriculture and food packaging by compression and injection molding followed by baking. Some typical prototype items have been prepared and characterized in relation to their morphological
Soil appearance at the end of the hydro-biomulching field trial.
Environmentally Degradable Bio-Based Polymeric Blends and Composites Emo Chiellini,*1 Patrizia Cinelli,1 Federica Chiellini,1 Syed H. Imam2 1
UdR Consortium INSTM, Department of Chemistry & Industrial Chemistry, University of Pisa, Via Risorgimento 35, 56126 Pisa, Italy Fax: þ39-050-28438; E-mail:
[email protected] 2 Bioproduct Chemistry & Engineering Research, USDA, ARS, WRRC, Albany, CA 94710, USA
Received: December 11, 2003; Revised: February 4, 2004; Accepted: February 4, 2004; DOI: 10.1002/mabi.200300126 Keywords: biodegradable; composites; natural fibres; poly(vinyl alcohol)
1. Introduction In the last decades, environmental protection has become a global concern providing much needed impetus for the development of alternative utilization of our natural resources. Currently, it is at the level of only 3.5% of the overall annual production estimated around 170 billion tons for food and non food consumption, which is quite comparable to the annual consumption of the fossil fuel feedstock (7.3 billion tons). However, about 93% of these last resources are used for energy production alone with Macromol. Biosci. 2004, 4, 218–231
consequent negative impact on green house gas emission balance, eventually leading to increase in the global warming and associated climate changes.[1] In this respect, efforts are underway world-wide to utilize renewable feedstock both as energy source[2] and as raw materials for the production of chemicals and polymeric materials and/or plastics.[3,4] The term ‘‘bio-based polymers’’ comprises polymeric materials obtained from renewable resources that can be processed to engineer plastic-like products of desired structural and functional properties for applications. Several
DOI: 10.1002/mabi.200300126
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major options for the production of consumer as well as high performance industrial grade plastic products from bio-based polymers are outlined in Figure 1. As an added advantage, products manufactured from bio-based polymeric materials will eventually be biodegraded after their useful service life is over. A wide variety of bio-based polymers are available in nature, which include polysaccharides such as cellulose, starch, chitosan, proteins like wool, silk and gelatins, oils and fats, lignin, polynucleotides, polyisoprenoids, as well as polymers derived from monomeric components obtained from renewable resources. Moreover, polymers from renewable resources may be broadly classified according to the source from which they are deriving. Natural polymers or biopolymers are synthesized in nature by living organism and by plants through sophisticated biosynthetic pathways requiring carbon dioxide consumption, and are ultimately degraded and recycled in order to maintain and encourage sustainability of resources.[5] Some natural polymers such as rubber, lignin and humus display a slow rate of biodegradation, since they are produced in nature there is no major concern for their environmental impact as ultimately
Figure 1. Major options for the production of environmentally degradable bio-based polymeric materials and plastics.
they are going to be mineralized. This concept if applied to synthetic and semi-synthetic polymeric materials and eventually to their hybrid composites may open new valuable scenarios in the production of environmentally viable plastic items. Another category of biopolymers include
Emo Chiellini is since 1980 Full Professor of Chemical Fundaments of Technologies at the Faculty of Engineering of the University of Pisa. In 1963 he graduated at the University of Pisa with a thesis on Polymer Science in the group of Prof. Piero Pino. Since then he continued his activity in Polymer Science & Technology at the Department of Chemistry & Industrial Chemistry of the University of Pisa and as a visiting scientist at the University of Liverpool (UK), University of Massachusetts at Amherst (USA) and University of Nagasaki (Japan). He is presently head of an interdisciplinary research group active in Polymer Science & Technology with specific interest in the field of Biodegradable Polymeric Materials for Biomedical, Pharmaceutical and Environmental Applications. He has served as member of the Editorial Boards of various scientific journals related to Polymer Science & Technology, including among the others Reactive Polymers, Macromolecules, Korea Polymer Journal, Biomacromolecules, Polymer Degradation & Stability, Journal of Bioactive Polymers, Journal of Polymers and Environment. He has chaired international conferences related to Polymers in Medicine, Liquid Crystalline Polymers, Biodegradable Polymeric Materials and Plastics and a Gordon Research Conference on Biodegradable Polymers in 1996. He is author and co-author of 400 publications in peer-reviewed journals, 20 books and 20 patents. The research group leaded by Prof. Chiellini is active in multipartner projects funded by Industries, Italian Ministry of University & Research, and European Community. He is currently acting as advisor in a research program on Sustainable Polymeric Materials and Environmentally Degradable Polymers launched by the International Centre for Science & High Technology under the UNIDO sponsorship. Patrizia Cinelli received the Laurea Degree in 1995 in Chemistry at the University of Florence by defending a Laurea thesis under the supervision of Prof. Dante Gatteschi. In 1996 she attended the ‘‘Specialization School in Materials Science and Technology’’ at the University of Genoa, Italy. In 1999 she obtained the Doctor Degree in Chemistry at the University of Pisa (Italy) by defending a thesis on ‘‘Formulation and Characterization of Environmentally Compatible Polymeric Materials for Agriculture Applications’’, under the supervision of Prof. Emo Chiellini and external supervision of Dr. S. H. Imam (USDA – Peoria, IL – USA). She is co-author of 30 papers in peer-reviewed journals, books and two patent applications. She is currently working as a postdoc in the research group of Prof. Chiellini in the field of polymeric materials for environmental applications and had the opportunity of performing part of the activity in the research group of Dr. Imam at the Laboratories of the United States Department of Agriculture (USDA), Peoria, Illinois – USA. She is actively participating in a multipartner project funded by European Commission and Industries, related to environmental and ecopackaging issues. Macromol. Biosci. 2004, 4, 218–231
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Federica Chiellini received the Laurea Degree in 1994 in Biology at the University of Pisa. In 1995 she joined the Biochemistry Group at the University of Gent (Belgium) as a Human Capital & Mobility Fellow. In 1996 she was appointed as a fellow at the Materials Science and Technology Interuniversity Consortium (INSTM) in the framework of a Brite-Euram European Project on ‘‘BioerodibleBiodegradable Polymeric Matrices for Targeted Protein Drug Release’’. In 1997 she was appointed as a PhD student in Biomaterials at the University of Trento and in year 2001 defended a Thesis on the ‘‘Synthesis and Chemical Biological Characterization of New Polymeric Materials Designed for Tissue Engineering Applications’’. In 2000 she was a visiting scientist at Cornell University (USA) at the Materials Science an Engineering Department and at the School of Chemical Engineering. Since 2001 she works at the University of Pisa as post-doc/research associate. She is responsible for the cell culture facility at the Laboratory of Polymeric Materials, Department of Chemistry & Industrial Chemistry. Her main research interests are the design and biological characterization of bioerodible/ biodegradable polymers for biomedical and environmental applications. She is co-author of over 25 publications in international journals and books and she is co-inventor of two patents. Syed H. Imam, a senior Research Chemist in the Bioproduct Chemistry & Engineering Research Unit at the USDA-WRRC in Albany, CA is internationally recognized for his accomplishments in the area of biodegradable plastics, which include polymer blending, characterization, aging/performance, as well as biodegradation. He has served on the American Society for Testing Materials (ASTM) – D20 Committee on ‘‘Biodegradable Polymers’’ and currently serving on the Editorial Advisory Board of the Journal of Polymers and the Environment. Dr. Imam has served as a United Nations Development Program (UNDP) consultant/mission advisor and has been invited to the joint International Center for Science – United Nations Industrial Development Organization (ICS/UNIDO) Expert Group Meetings on Biodegradable Polymers in Bratislava (Slovakia), Trieste (Italy) and Jakarta (Indonesia). Has published over 100 research articles, reviews and book chapters, and served as a chief editor of ACS Book titled ‘‘Biopolymers: Utilizing Nature’s Advanced Materials’’ published by the Oxford University Press in 1999. He has served as thesis advisor for numerous graduate students from numerous international institutions and is the co-organizer and Program Director of the ARS-Mexico International Workshops on ‘‘Agriculture and Biotechnology’’ held biannually at Universidad Autonoma de Nuevo Leon, Monterrey, Mexico. Additionally, he has organized international meetings, numerous symposiums at national and international meetings and served on the international scientific advisory committees of international congresses. In the year 2000, Dr. Imam’s joint research with collaborators from Italy and Egypt was nominated for the Germany’s prestigious ‘‘Braunsweig Prize’’ in the field of agriculture.
‘‘artificial polymers’’ such as cellulose esters and ethers obtained by chemical modification of naturally occurring polymers as well as polylactate obtained from starch bio-derived lactic acid. Other polymeric materials such as bacterial polysaccharides, as well as array of polyesters [poly(hydroxy alkanoates)] produced by the native as well as genetically transformed microorganisms have only been marginally assessed for their potential, and continue to be the major focus of several laboratories around the world. Important contributions to the development of the field of polymeric materials from renewable resources may indeed come from our knowledge of polymer assembly at the molecular level and complete understanding biosynthetic pathways that are critical in imparting chemical and biological functionalities in a biological polymer. These tools may impede our efforts in identification, isolation and modification of potentially valuable candidates, which could be transformed into higher-yielding production systems with tailored polymeric structures. The bio-based polymeric materials are relatively inexpensive, ecocompatible, and designed to experience environmental degradation. Particularly, fibrous material Macromol. Biosci. 2004, 4, 218–231
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derived from renewable crops, by-products or their industrially processed wastes can be considered a good polymer source in formulations for preparing blends and composites in conjunction with either synthetic (hybrids) or natural components that we name ‘‘natcos’’ for quick identification.[6] Poly(vinyl alcohol) (PVA) is a particularly well suited synthetic polymer for the formulation of blends with natural polymers since it is highly polar and can also be manipulated in water solutions and depending upon its specific grade in functional organic solvents as well as processed from the melt.[7–9] Ongoing investigation in our laboratories on the formulation and applicability of mixtures of PVA, as synthetic water soluble polymeric material, and bio-based ‘‘fillers’’ from low-value agro-industrial waste, has highlighted the potential of attaining ecocompatible articles meant to experience environmental degradation at the end of their service life that eventually can be programmed. Ongoing research cooperation between USDA and University of Pisa, Italy has led to the development of several blends and composites based on PVA and lignocellulosic ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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components derived from agro-industrial waste derived from sugar cane, citrus fruits, corn, wheat and wood processing.[10,11] In the present contribution, a review is provided to capture the highlights of the current status of the field based on our joint research of the past few years. Particularly, efforts on developing formulations for blends and composites (both hybrid and natcos systems) along with processing parameters, resulting properties and potential applications are described.
2. Hybrid Polymer Composites for Hydro-Biomulching Practice 2.1 Formulations Based on Poly(vinyl alcohol) (PVA) and Different Agro-Industrial Wastes In the past mulch practice has been performed by the use of natural materials such as straw and leaves to provide an insulating layer around the roots of vegetables and soft fruits. Actually the use of plastic sheets or films in mulching is the largest single application of plastics in agriculture. Mulch controls radiation, soil temperature and humidity, weed growth, insect infestation, soil compaction, and the degree of carbon dioxide retention. A mulching effect or a conditioning effect on soil structure can also be obtained by the technique referred to as ‘‘hydro-biomulching’’ or ‘‘liquid mulching’’.[12] Due to their water solubility some synthetic degradable polymers such as poly(acrylamide), poly(vinyl alcohol), carboxymethyl cellulose, and hydrolyzed starch-g-polyacrylonitrile (HSPAN), can be easily sprayed on the soil alone or in mixture with nutrients or other mulching materials, basically indicated as ‘‘fillers’’.[13–16] Tackyfiers helping to hold the mulch in place once applied or aimed at forming a sort of thatch intended to protect seeds and soil against erosion, constitute essential smart filler ingredients. As a part of a research program aimed at the preparation through the conventional processing technologies (casting from solution, melt blow extrusion, and injection-compression molding) and evaluation of environmentally degradable polymers for various applications in agricultural practices, with specific reference to the in situ formulation of self-fertilizing mulching films, we started to consider the possibility of utilizing poly(vinylacohol) (PVA) and fillers from renewable resources such as wheat straw, saw dust and sugar cane bagasse- the lignocellulosic residue deriving from sugar cane juice extraction.[17–20] PVA grade 8/88 Mowiol, 88% hydrolysis degree, M n 67 000 D, was used for hydro-biomulching formulations. Sugarcane bagasse (SCB) (Brasil) was in a powder form (f < 0.212 mm), constituted by: 42.6% crude fibres, 29.2% cellulose, 10.5% lignin, 9.1% crude protein, 2.6% fat, 6.0% ash. Wheat flour (WF) was a white thin powder (Italy), with composition: 45.4% starch, 2.0% ash, 2.2% cellulose, 34.8% hard fibre, and 15.5% moisture. Wheat straw (WS) Macromol. Biosci. 2004, 4, 218–231
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was coarsely milled to an average size of 20 mm. Saw dust (SD) was a commercial daily product from soft wood sawing. In a field trial carried out at the University of Pisa between June and September, two conventional mulching materials: polyethylene film (PE) (70 g m2) and wheat straw mulching (SM) (100 g m2) were compared with PVA based innovative hydro-biomulching formulations. Data relevant to the indicated experiment set are collected in Table 1. PVA/SCB and PVA/WF water suspensions were sprayed on the soil by an air compressor, working at 3 bar pressure and equipped with a 2.5 mm nozzle. Saw dust and wheat straw were directly spread on the soil (500 g m2) prior to the spray application of the PVA solution. The PE film and the SM mulching were kept in place by nails and by net and nails, respectively. Corn (Zea mays) and lettuce (Lactuca sativa) were chosen to test the agronomic effect of the mulching treatments on a seeded and a transplanted crop respectively. For each plot three corn plants were established by sowing and three plants of lettuce were established by seedling transplanting. The height and dry biomass of the growing corn plant were measured on the days 30 and 60 of the experiment. Sixty days after sowing, the total leaf surface area of corn harvested plants was also determined.[21] All the lettuce plants were harvested fifty days after transplanting and dry biomass was measured and reported as average plant biomass. Results relevant to the different trials are collected in Table 2. In thirty days, corn height and biomass production in SM and PE values were significantly higher compared to the control. The differences were more notable after sixty days of sowing. While the SM behaved similar to control, the fluid mulching performed better than the untreated soil and with efficiency similar to that of the PE. Compared to corn, lettuce showed different effects of the mulching treatments. The effect of SM did not show a statistically significant difference from the control. While the PE promoted a growth significantly higher than the control, surprisingly, the investigated hydro-biomulching treatments used in our experiments exhibited much higher biomass production.
Table 1. Hybrid composite formulations based on PVA and lignocellulosic fillers. SCB ¼ Sugar Cane Bagasse, WF ¼ Wheat Flour, WS ¼ Wheat Straw (milled), SD ¼ Saw Dust. Treatment
SCB WF WS SD
PVA
Organic Filler
Water
g m2
Type
g m2
g m2
20 20 20 20
SCB WF WS SD
40 40 500 500
340 340 380 380
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Table 2. Results of mulching experiments carried out on corn and lettuce growing in field trials. SCB ¼ Sugar Cane Bagasse, WF ¼ Wheat Flour, WS ¼ Wheat Straw (milled), SD ¼ Saw Dust, SM ¼ Straw Mulch, PE ¼ Polyethylene. Mulching type
Zea mays
Lactuca sativa
Plant height 30 daysa) Dry biomass 30 daysa) Dry biomass 60 daysa) Total leaf area 60 daysb) Dry biomass 50 daysb)
SCB WF WS SD SM PE Control a) b)
cm
g per plant
g per plant
m2 per plant
g per plant
17.9 17.6 19.0 17.9 22.4 23.1 14.1
0.4 0.5 0.5 0.8 1.0 0.9 0.5
70.7 55.3 58.2 70.3 47.8 91.4 31.8
0.25 0.20 0.18 0.26 0.18 0.27 0.12
15.9 15.9 20.1 17.9 11.4 14.3 8.2
After sowing. After transplanting.
Remarkable differences were observed in the soil structure at the end of the experiment. Figure 2 shows the soil surface at the end of the trial in plots that had been treated with PVA/SCB, PVA/WF and the control (no mulching treatment). Soil aggregates (1–2 cm) were still present in treated soil, but were completely absent in the control plot. SCB presence conferred a dark brown colour to the soil and further research is warranted to explore their potential as a heat absorbent or as a UV blocker. Moreover, the data indicated that SCB and WF presence enhanced PVA time of permanence on the soil thus guaranteeing for the resulting soil structuring effect.
2.2 Hybrid Films Based on Gelatin, Poly(vinyl alcohol) and Agro-Industrial Waste Among naturally occurring polymers, gelatin offers good processability properties both in aqueous media and in the
Figure 2. Macromol. Biosci. 2004, 4, 218–231
melt. It exhibits also good film forming properties, and adheres well to a variety of substrates.[22] Gelatin is a high molecular weight polypeptides produced by denaturation and/or physical-chemical degradation of collagen, which is the primary protein component of animal connective tissues, such as bone, skin, and tendons.[23] The use of gelatin scraps, and byproducts from pharmaceutical, agricultural and tannery industries constitute an abundant source of gelatin protein. Development of applications for the use of such low-value, natural and biodegradable raw material will add value to farm byproducts. We developed formulations where waste gelatin scraps (WG) were provided by a pharmaceutical company (Rp Scherer, Egypt). WG scraps were used as received and contained several additives from original formulation as pigments and glycerol.[9] After dissolution in water, WG samples were added to sugarcane bagasse to formulate protein-cellulose dispersions. This technology is particularly useful for adaptation in countries where gelatin source and sugarcane bagasse
Soil appearance at the end of the hydro-biomulching field trial. www.mbs-journal.de
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are available as raw materials to produce low cost, in-situ formulations of environmentally degradable hydro-biomulching. A series of experiments was performed by spraying gelatin based water dispersions on pots, containing loamy soil, with an overall surface area of 154 cm2. The compositions of film formulations sprayed on the loamy soil are indicated in Table 3. The pots were left outdoors under open-air along with control, which did not receive any treatment. Films were obtained by the direct spraying technique on soil with the aim of testing the feasibility of a single pot application in field experiments. The evolution of film morphology formed on loamy soils was monitored for three weeks. The results of sprayed film experiments showed that the films lasted for more than two weeks on the soil and the soil appeared to be conditioned and in a better state when compared with the control sample. It is worth mentioning that, during the experiment time the boots containing the sprayed films were exposed to outdoor conditions that were monitored for all the duration of the experiment.[24]
3. Bio-Based Polymeric Blends and Composites – Processing and Mechanical Characterization 3.1 Hybrid Films by Casting from Water Solution or Dispersion 3.1.1 Films based on waste gelatin (WG), poly(vinyl alcohol) (PVA) and sugar cane bagasse (SCB) Waste Gelatin (WG) based films were cast from solutions or dispersions containing WG and either PVA or SCB components by slow evaporation of the water at room temperature and at atmospheric pressure.[9] Low molar mass dialdehydes and high molecular weight dialdehydes are the most popular crosslinking reagents, especially for protein materials as the amino groups arising from lysine react easily at room temperature with aldehyde groups.[25] Glutaraldehyde was used as crosslinking agent to improve water resistance and regulate degradation rate in soil of the hybrid films (Table 4).[26] Table 3. Composition of sprayed films based on waste gelatin (WG), polyvinyl alcohol (PVA), sugar cane bagasse (SCB) and glutaraldehyde as crosslinker (X). Film Sample
WGSCB5 WGSCB5X WGPSCB WGPSCBX
Waste Gelatin
PVA
Bagasse
X
%
%
%
%
50 50 40 40
– – 10 10
50 49.75 50 49.75
– 0.25 – 0.25
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Table 4. Composition of blends based on waste gelatin (WG), poly(vinyl alcohol) and sugar cane bagasse (SCB). P ¼ Poly(vinyl alcohol) (PVA), X ¼ Glutaraldehyde. Sample
WG WGP10 WGP20 WGP30 WGP50 WGP80 WGP90 PVA WGP80X WGX1 WGX2 WGX3 WGSCB20 WGSCB20X
WG
PVA
SCB
X
%
%
%
%
– – – – – – – – – – – – 20 20
– – – – – – – – 0.25 0.25 1.00 2.50 – 0.25
100 90 80 70 50 20 10 – 20 99.75 99 97.5 80 79.75
– 10 20 30 50 80 90 100 79.75 – – – – –
WG cast films appeared red coloured, translucent, flexible, with small amounts of insoluble residues dispersed in the gelatin matrix. The mechanical properties of WG corresponded to WG plasticised by water and glycerol present in the scraps. WG cast films had elongation at break (El) of 116%, ultimate tensile strength (UTS) of 11 MPa and Young’s modulus (YM) of 78 MPa (Table 5). Addition of up to 20% of WG to PVA (WGP90, WGP80) increased the El from 211% for pure PVA up to 257% for WGP80 and reduced both the UTS and YM, as reported in Table 5. This behaviour can be attributed to the plasticizing effect of glycerol present in WG. Blends with higher concentration of WG exhibited mechanical properties that were equivalent to that of pure WG. Table 5. Mechanical properties and relevant standard deviations (StDv) of waste gelatin (WG) based blends. El ¼ Elongation at Break, UTS ¼ Ultimate Tensile Strength, YM ¼ Young Modulus, StDv ¼ Standard Deviation. Samplea)
El
StDv
% WG WGP50 WGP70 WGP80 WGP90 PVA WGP80X WGX1 WGX2 WGX3 WGSCB20 WGSCB20X a)
116 133 132 257 235 211 241 146 140 300 14 14
UTS
StDv
MPa 22 13 14 28 24 26 23 16 29 17 2.1 2.6
11 8.3 14 22 26 35 22 10 10 13 10 11
YM
StDv
MPa 1.2 0.9 0.5 2.3 0.8 3.1 1.9 1.6 2.5 2.0 0.9 1.5
78 79 86 133 200 387 128 33 33 10 228 283
12 17 14 13 45 63 15 1 7 3 27 21
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Figure 3.
SEM micrographs of WGB20 surface and fracture.
The addition of SCB fibres to WG hardened the resulting films and darkened film colour. Accordingly, films of WG containing 10–30% SCB were rather flexible, whereas films containing 40–50% SCB were very hard and brittle. An 80:20 WG/SCB blend (WGSCB20) appeared to be the most interesting composition as far as filler content and mechanical properties were concerned. WG and SCB were quite compatible, and showed a good interfacial adhesion (Figure 3). This WG/SCB weight ratio appeared to be adequate to completely cover and aggregate SCB fibres in the continuous matrix. Due to the casting process, SCB fibres presented a random distribution and formed fibres aggregates thus reducing El as showed by tensile tests. Indeed WG cast film presented 116% El while in WGSCB20 El was 14%. UTS were almost the same and YM increased from 78 MPa for WG to 228 MPa for WGSCB20. Hardening of gelatin with low molecular weight aldehydes is well documented in the literature.[27,28] Crosslinking is predominantly due to Schiff’s base formation by condensation of the aldehyde group and the e-amino groups present in lysine and hydroxylysine residues. El in WG cast films increased significantly when the glutaraldehyde was introduced in the formulations as reported in Table 5. Thus depending upon crosslinking density, temperature and diluent content a gelatin specimen can behave as a rubber-like material capable of extending by 700% or as a viscous liquid.[29] For a crosslinker content of 0.25%, as in WGX1, El was 140% increasing to 300% for 2.5% of glutaraldehyde content as in WGX3. At the same time YM decreased from 78 MPa in WG up to 10 MPa for WGX3, whereas UTS did not significantly change. This Table 6. Fibres
SCB OR AP
behavior of gelatin can be attributed to the disruption of the helical structure of native gelatin allowing the chains to assume a random coil conformation with glutaraldehyde acting as a crosslinker among the chains.[30] On the other hand, WGP80X and WGSCB20X did not show any significant difference in comparison with WGP80 and WGSCB20, thus indicating that 0.25% of glutaraldehyde has a negligible effect on blend properties, also in accordance with results from previous studies of water sensitivity and mineralization rates.[26,31]
3.1.2 Films Based on PVA and Natural Fillers from Agro-Industrial Waste PVA Airvol 425 from Air Products & Chemicals Inc., had Mn 100–146 KDa and 96% hydrolysis degree. Unmodified commercial-grade corn/starch (USA) had approximately 30% amylose and 70% amylopectin content. Cellulosic materials were from three different sources; sugarcane bagasse (SCB) (USA), orange (OR) (Pakistan) and apple (AP) (USA) peel were the remains of fruit residue after juice extraction.[32] Composition and moisture content data of the selected agro-industrial waste are collected in Table 6. All cellulosic materials were milled, sieved to obtain particles sizes
