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SID 5 Research Project Final Report

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NoteIn line with the Freedom of Information Act 2000, Defra aims to place the results of its completed research projects in the public domain wherever possible. The SID 5 (Research Project Final Report) is designed to capture the information on the results and outputs of Defra-funded research in a format that is easily publishable through the Defra website. A SID 5 must be completed for all projects.

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Project identification

1. Defra Project code CSA6732/NF0608

2. Project title

Modified starch containing silane moieties

3. Contractororganisation(s)

The BioComposites CentreUniversity of WalesBangorGwyneddLL57 2UW

     Stadex Industries LtdCoed Aben RoadWrexham Industrial EstateWrexhamClwydLL13 9UL

54. Total Defra project costs £ 67913.13(agreed fixed price)

5. Project: start date................ 01 January 2005

end date................. 31 January 2005

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6. It is Defra’s intention to publish this form. Please confirm your agreement to do so...................................................................................YES NO (a) When preparing SID 5s contractors should bear in mind that Defra intends that they be made public. They

should be written in a clear and concise manner and represent a full account of the research project which someone not closely associated with the project can follow.Defra recognises that in a small minority of cases there may be information, such as intellectual property or commercially confidential data, used in or generated by the research project, which should not be disclosed. In these cases, such information should be detailed in a separate annex (not to be published) so that the SID 5 can be placed in the public domain. Where it is impossible to complete the Final Report without including references to any sensitive or confidential data, the information should be included and section (b) completed. NB: only in exceptional circumstances will Defra expect contractors to give a "No" answer.In all cases, reasons for withholding information must be fully in line with exemptions under the Environmental Information Regulations or the Freedom of Information Act 2000.

(b) If you have answered NO, please explain why the Final report should not be released into public domain

Executive Summary7. The executive summary must not exceed 2 sides in total of A4 and should be understandable to the

intelligent non-scientist. It should cover the main objectives, methods and findings of the research, together with any other significant events and options for new work.

A novel procedure has been found to modify starch with silane containing moities. The methodology involves the reaction of alkoxysilanes with starch in aqueous basic or acidic solutions at room temperatures, representing a major advance over previous techniques which lead to the production of toxic by-products. A range of derivatives has been obtained using such methodology and these have been tested in a range of industrial end-uses.The first investigated application was the production of baked starch foam packaging. Using silane starches as an additive, starch foam trays, produced by baking technology can now be hydrophobic, allowing them to be used in the packaging of wet fruits and vegetables (like tomatoes). Additionally, silane starches have also been shown to impart hydrophobicity to paper. The hydrophobicity that is obtained is higher than that which can be obtained using other commercially available alternatives tested during this project, i.e polyvinyl alcohol and alkylketene dimer. It has been found that baked starch trays containing just 2% of silane starch additive have twice the strength of trays manufactured from unmodified starch, which would allow the production of thinner starch trays. This reduction in weight is expected to improve competitivity of starch based materials over non-renewable based alternatives.As novel thixotropic paint additives, the silane starches tested have no major advantage over hydroxyethylcellulose, which is currently the standard material used in the field. However, because it has been shown that they can impart heat resistance they have now been suggested to be used in the formulation of drilling muds. Drilling muds are used as coatings to protect the walls of petroleum bore holes during drilling and should resist the high underground temperatures.The fact that resistance to high temperature can be imparted to natural flax fibers is an indication of its potential use as a fire retardant, however formulations that would use commercially available synergetic materials (other charring agents-phosphates or borates, and radical scavengers- that can act in the gas phase or heat sinks) still need to be developed.The chemistry developed is also expected to lead to processing alternatives to the “green tyre”. These have been introduced recently as new tyres, which formulated with rubber modified with thermoplastic starch and silane-sulfur, have outstandingly low attrition and for a given travel distance, allow cars to consume less energy. Formulation, however, implies the use of very high mechanical energy to bind starch to the silanes. The fact that this reaction can be done catalytically at room temperature and in water suggest that energy needed to produce such rubber materials can also be reduced. This work is to be done in the future.

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Project Report to Defra8. As a guide this report should be no longer than 20 sides of A4. This report is to provide Defra with

details of the outputs of the research project for internal purposes; to meet the terms of the contract; and to allow Defra to publish details of the outputs to meet Environmental Information Regulation or Freedom of Information obligations. This short report to Defra does not preclude contractors from also seeking to publish a full, formal scientific report/paper in an appropriate scientific or other journal/publication. Indeed, Defra actively encourages such publications as part of the contract terms. The report to Defra should include: the scientific objectives as set out in the contract; the extent to which the objectives set out in the contract have been met; details of methods used and the results obtained, including statistical analysis (if appropriate); a discussion of the results and their reliability; the main implications of the findings; possible future work; and any action resulting from the research (e.g. IP, Knowledge Transfer).

PART A. Development of new procedures for the production of a range of silane starch derivatives

A1. Introduction

Starch is the common name for a complex mixture of carbohydrate, (C6H10O5)x. Molecules of starch are made from hundreds or thousands of atoms, corresponding to values of x, as given in the formula above, that range from about 50 to many thousands. Starch molecules are of two kinds. In the first kind, amylose, the C6H10O5 groups are arranged in a continuous but curled chain somewhat like a coil of rope; in the second kind, amylopectin, considerable side-branching of the molecule occurs. These two kind of molecules are entwined, to form starch granules. But, being also a polymeric mixture based on anhydroglucose units, the two main routes for the chemical modifications of starches are reactions with the hydroxyl groups or with the glucosidic (C–O–C) linkages. Hydroxyl groups are subject to standard substitution reactions (esterification, etherification) and the glucosidic linkages are subject to cleavage of the carbon oxygen bond (oxidation, enzyme conversion). Silylation falls in the first category. Silylated starches are expected to provide higher mechanical properties than etherified starches, because the silicon-oxygen bond is stronger than the carbon-oxygen one. Furthermore, other physical properties are expected to improve (thermal resistance, etc..). Recently, Goodyear introduced tyres manufactured with silylated starch, indicating that they would decrease fuel consumption, lower CO2 emissions and reduce road noise.1

A2. Project objectives

The present starch silylation study comprises two parts:

1. The development of cheap, environmentally sound chemistry to produce silylated starches. A range of modified starches are expected to be produced from the two most common commercial starches in the UK (wheat and potato starches) as well as from enriched amylose/ amylopectin starches. Modification will be by variation of the degree of substitution of the anhydroglucose unit with a range of silylating agents.

2. The investigation of a range of end use applications (see later for details) involves the possible use of these compounds as a new paper wet-end additive, a coating agent, a hydrophobic agent in the manufacture of starch foam trays, a fire retardant agent and in the development of new lightweight concrete.

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A3. General information on chemistry

Industrial interest in the project came from Stadex Industries, a company based in Wrexham, manufacturing wallpaper pastes and oil drilling muds, amongst others. Stadex made clear that modification of starches should be carried out with chemistry using mainly water as a reaction medium, with reduced or non-waste generating methodology. This practically eliminated the potential use of water sensitive chlorosilane, which is the most common agent of silylation.

Bulk silylation of natural polysaccharides using chlorosilanes has been reported,2 but this approach would not eliminate another problem: the emergence of by-products in the reaction mixture as hydrochlorhydric acid, or its salts, which result from the need to inhibit acid induced degradation/depolymerisation of the polysaccharide.

As a reagent that does not form hydrogen chloride, hexamethylenedisilizane is most commonly used, but leads to the generation of ammonia as a by-product.3 A review on the state of art of silylation of (cellulose and) starch recently published summarizes these findings,4

and compares a range of solvents (N,N-dimethylacetamide/LiCl, and N-methylpyrrolidone/ammonia) used to perform substitution reactions.

Silylation could also be performed using hydrosilanes, in presence of catalysts such as tetrabutylammoniumfluoride and the like. In those cases, the by-product is hydrogen gas, which can be easily eliminated from the products, but has the disadvantage to increase the risk of a potential explosion.5 Silanols have also been proposed, in a process where an alcohol and a silanol are subjected to a dehydrative condensation under Mitsonubu reaction conditions, but expensive reagents are used and large amounts of by-products are generated.6

Attention has been turned to the use of alkoxysilane molecules, currently used in the building industry for the protection of masonry, for sizing of glass fibres.7 These are investigated as coupling agents in wood plastic composites,8 ingredients in scratch resistant surfaces and anti-graffiti coatings,9 as well as treatment agents for the hydrophobisation and improving the dimensional stability of wood.10 Similarly, the modification of cellulose has been reported using alkoxysilanes, with polar non-aqueous solvents (NMP, DMAC, NMO, or primary alcohols).11

The purpose of this work therefore was to establish a general procedure to introduce silane moieties into starches using if possible water or other ‘green’, environmentally benign solvent, and to tune up the parameters to analyse different end-uses for the produced starches.

A4. Results and discussion

The most straightforward and easy method of substitution of starch with an alkoxysilane reagent should it be successful was heterogeneous treatment of starch granules with the appropriate alkoxysilane, with heating.

Figure 1 General reaction of a thermoactivated alkoxysilane with starch

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However, as in the case of cellulose fibres, reported recently by Castellano,12 there was no detectable coupling of organo-silane to starch even at high temperature (organo-silane with starch at 80 ºC). Castellano and collaborators have also shown that moisture induces partial hydrolysis of siloxane moieties, but that these can react with polysaccharides only at high temperature.

Figure 2 General reaction of alkoxysilane with starch in alcaline medium

However, we have found that the reaction could be successfully performed at room temperature under catalytic conditions, as a range of silylated starches was obtained by reacting a solution of organosilane, in either alkaline or acid conditions (either sodium hydroxide, potassium hydroxide, or acetic acid), with an aqueous solution of starch.

A typical solid state silicon nuclear magnetic resonance spectrum of such modified starches is presented in Figure 3. The spectrum shows three distinct chemical environments for silicon moieties: one is characteristic of silane-alkyl moieties at δ12.752, while the signals centred on δ107.337–108.647 are characteristic of the silane-oxygen-silane functionality,13 and the signal at δ65.625–65.924 is characteristic of a silane-oxygen-carbon (i.e., polysaccharide-silane) bond.

Figure 3 Silicon NMR of trimethoxysilane modified potato starch, with a DS 2.5

Samples with very low degree of substitution (DS 0.01–0.06) only showed signals at δ-65.625–65.924, showing that silane–silane reactions are concentration dependent. In the case of low DS pine fibre-silane coupling (obtained via dehydrochlorination of diethyldichlorosilane in the

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presence of wood fibres), an equivalent Si NMR chemical shift was reported14 consistent with our observations.

Alkoxysilane and aqueous systems were found to be a potential new solvent system for cheap starch silylation.

We note that FTIR spectroscopic analysis, which is commonly used in the identification of chemically modified starches, was not suitable for the characterisation of the starch silane compounds. This is due to the overlap of the free hydroxyl groups from the newly formed silanol moieties with the non-substituted hydroxyl groups of the starch substrate.

Both wheat and potato starches have been reacted similarly and a range of derivatives of these two starches with most cheap commercially available alkoxysilanes, as indicated in Table 1, were obtained under both alkaline and acidic catalytic conditions.

SampleID

Type of starch

Alkoxysilane Catalyst Degree of substitution

Observations

P1 Potato Trimethoxymethylsilane NaOH 0.02W1 Wheat Trimethoxymethylsilane NaOH 0.02P2 Potato Trimethoxymethylsilane NaOH 1.30W2 Wheat Trimethoxymethylsilane NaOH 0.92P3 Potato Trimethoxymethylsilane KOH 0.06 Very easy to

filter, low silane losses

W2 Wheat Trimethoxymethylsilane KOH 0.02 Very easy to filter

P4 Potato Trimethoxymethylsilane KOH 2.5 Very easy to filter

W3 Wheat Trimethoxymethylsilane KOH 2.5 Very easy to filter

P5 Potato Trimethoxymethylsilane H2SO4(dil.) 0.34W4 Wheat Trimethoxymethylsilane H2SO4(dil) 0.22P6 Potato Trimethoxymethylsilane pTsOH 0.56W5 Wheat Trimethoxymethylsilane pTsOH 0.44P7 Potato Trimethoxymethylsilane acetic acid 0.45W6 Wheat Trimethoxymethylsilane acetic acid 0.56P8 Potato Trimethoxymethylsilane Triethyl

amine2.47

W7 Wheat Trimethoxymethylsilane Triethylamine

2.26

P9 Potato Trimethoxymethylsilane Pyridine 2.50 Pyridine smellW8 Wheat Trimethoxymethylsilane Pyridine 2.45 Pyridine smellP10 Potato Trimethoxypropylsilane KOH 0.02W9 Wheat Trimethoxypropylsilane KOH 0.02P11 Potato Trimethoxyisobutylsilane KOH 2.45W10 Wheat Trimethoxyisobutylsilane KOH 2.45P12 Potato Triethoxyoctylsilane KOH 1.2 Only 15%

silane chemically bonded

P13 Potato TriethylAmine

2.2 36 % silane chemically bonded

P14 Potato Triethoxyoctylsilane pTsOH 0.08 Only 12% silane chemically bonded

P15 Potato Trimethoxymethacrylate KOH 1.6W11 Wheat Trimethoxymethacrylate KOH 1.6P16 Potato Trimethoxymethacrylate pTsOH 1.2W12 Wheat Trimethoxymethacrylate pTsOH 1.2

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Table 1 List of modified starches produced in the project

A first screening of the reaction conditions was performed using either potato or wheat starches and trimethoxymethylsilane, and a range of catalysts. Product analysis (elemental analysis), show that part of the silane used in the reaction is chemically binded to the starch, the remaining quantity being present in the aqueous layer. Lower losses were obtained with potassium hydroxide (KOH) and triethylamine, which in general allowed 50–60% of silicon material to be bound to starch, while high losses (only 30–35% of silane reacted) were observed when dilute sulfuric acid (H2SO4, dil) and paratoluene sulfonic acid where used as catalysts).

When trimethoxypropylsilane was used instead of trimethoxymethylsilane, no major difference in terms of % of silane reacted could be observed, but when triethoxyoctylsilane was used, a surprisingly low 15% of silane reacted was obtained. Upon changing catalyst, to allow different interfacial contact between the two reagents, little improvement of the yield of the reaction was observed. We believe this is largely due to phase separation of the rather hydrophobic octyl-substituted silane and the aqueous starch reaction mixture. Trimethoxymethacrylate provided relatively high yield of modified starch under both acid and base catalysis.

The silane starches produced have high viscosity even at very low DS. When the DS was increased, then the resulting samples became insoluble in all of the common solvents used in laboratory experiments (water, methanol, ethanol, DMSO, ethyl acetate, tetrahydrofuran, chloroform, dichloromethane or petroleum ether). This result is consistent with the NMR indication that a) at low DS, alkoxysilane can be bonded to starch, but that b) at a higher DS a solvent-insoluble thin distribution of chemical entities with silane-oxygen-silane bond cover the starch macromolecules.

A5. Proposed method of production

A method of production, which would make major use of the existing infrastructures of the industrial partner, was proposed, as set out in Figure 4.

Figure 4 Proposed industrial manufacturing scheme for silane starch production

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As indicated in Figure 4, the starch substrate could be mixed with the alkoxysilane, and recycled solvent (water with unreacted silane, and silane hydroxide, and catalyst, from a previous batch). After reaction, the resulting prodcut would be filtered and subsequently dried in a two roll drier system. In subsequent experiments it was found that filtration time could be reduced, without reducing the amount of reacted silane if ethanol was used as a solvent. However, it is not known at this stage if the company would/could use such technology.

Certain of the applications investigated (see later) do not require drying of the modified starch and the possibility of producing aqueous suspensions needs to be evaluated as a function of market needs.

PART B. Development of industrial uses of the silylated starches

B1. Paper additive

It is in the manufacture of paper that starch finds its major non-food use in the UK. 15 It is used in the wet end, for surface sizing, and in the coating process.16 Silylated starches are expected to provide hydrophobicity and be used to produce grease resistant paper (could be used in packaging greasy foodstuffs such as butter).

A qualitative wetting test was devised to measure hydrophobicity. Briefly, a sample of modified starch (dried and milled) was added to 250 ml of water at 20 ºC and the time taken to wet out and sink was measured. The test duration was 24 h. Native starch sank immediately to the bottom of the beaker. It was shown that hydrophobic starches could be obtained by reacting 0.01 moles equivalents methyltrimethoxysilane per each mol of anhydroglucose of the starch polymer. Such materials remained unwettable after 24 h. By comparison, the same quantity of aqueous solution starch treated with the same amount of methyltrimethoxysilane but without catalyst was immediately wetted in water and sank to the bottom of the beaker glass.

A thin coat of silanated starch on paper results in hydrophobic character, as shown in Figure 5.

Figure 5 Silane starch-treated paper

In Figure 5, in the case of (1) a drop of water (coloured to aid visualisation) is not absorbed by the paper and forms a non-wetting bead; conversely in (2) a drop of methanol is almost instantaneously absorbed.

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A variation of the contact angle function of the degree of substitution is shown in the figure

It is expected that the Industrial Partner would use the potential demonstrated in its range of products sold to the paper industry.

B2. Baked foam

Potatopak developed baked foam (when the study was performed) as the major structural component of biodegradable packaging trays for vegetables. Production capacity was very small. Produce Packaging (a company involved in supplying packaging to supermarkets) indicated that the consumption of only one of the main supermarkets would be in the range of 8000 tonnes equivalent starch/year if costs could be lowered and quality- i.e.tray impermeability, could be improved. In other countries, a polycaprolactone resin is coated on the tray to prevent liquid egress from the tray.17,18

It was expected that silylated starch would improve the hydrophobicity of the tray. The cost of raw materials to produce silylated starch using a literature procedure is two times lower than the present price of caprolactone suggesting that this modified starch will be cheaper than polycaprolactone. A study in the factory to minimise the production cycle was to be carried out to allow the possible industrial production of foam trays.

Previous work done by PotatoPak showed that batters of starch and water can readily be baked in a closed, heated mould, where the starch granules gelatinise and the evaporation of water causes the starch to foam and take the shape of the mold.19 Foams made of starch have major drawbacks on 1) their brittleness and 2) sensitivity to moisture and water, 3) the relatively high cost of the trays. Discussion with PotatoPak suggested that the high cost of the trays was due to a) very low production capacity, and b) very high quantity of starch used. Starch is cheaper than polystyrene (roughly half of the price of polystyrene) but on a weight basis 3.5 units of starch are used instead of one unit of EPS to produce a tray, and therefore either the density of the starch trays should be reduced or the possibility of adding inert fillers or cheaper raw-materials instead of starch needed to be investigated to provide a commercial product.

Our experimental strategy was devised to determine whether or not silane starch could a) improve hydrophobicity of the trays, b) improve strength and therefore allow the reduction of the thickness and weight of the trays. Additionally, the strategy included to check if other untested, commercially available additives (AKD, alkyketene dimer, used in the paper industry as an hydrophobic agent, and polyvinylalcohol, as literature indicated that that water resistance could be improved by adding it to the batter before baking20 ) could provide better results on a cost/ performance basis.

Experiments were performed using PotatoPak equipment, in which a batter is pumped through a mould, where the batter is heated for 115 seconds. However, the viscosity of the starch silane was too high to be pumped trough the equipment. And therefore batters with 0.5–2 % silane starches as additives (balance being native starch) were used to produce trays. Guar gum, cellulose fibres and magnesium steareate were used as in the standard PotatoPack formula.

An example of starch trays produced is shown in Figure 6.

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Figure 6 Baked starch trays produced by Potato Pak incorporating silane starch additive

A comparison was made between samples that were prepared with 2 % PVA (88% hydrolyzed and had an average molecular weight of 85,000–124,000) or 2 % AKD (Raisio 230) instead of using silane starch. Alkylketene dimer was rapidly ruled out as a competing additive as it decomposed during the manufacture of the trays to afford free organic acids with a strong smell, which could not be eliminated easily.

An additional approach to reduce raw materials’ costs was to check the possible use of mash potato (containing 1.9% protein) instead of potato starch. Unfortunately, with such changes all trays were very brittle, and had a light brown colour which suggested that brittleness may be related to a Maillard reaction (between sugars and proteins). Extraction of the mash with water, and use of fresh water for the batter allowed to obtain trays with no brittleness (see entries A10 and A11 in Table 2), suggesting that fresh potato could be used directly on the plant or that part of the starch may be substituted by mashed potato produced in the factory. The extraction process is far simpler than the separation of potato starch from the respective mash, and may allow, on the basis that there are economically feasible plants processing potato starch at a lower capacity than the one corresponding to the market for food trays in the UK, the direct use of potatoes in a potato starch plant. Furthermore, on the basis that some varieties of potato have a high starch content, but are produced only in continental Europe, the possibility of using directly such potatoes in a food tray factory need to be investigated as a way of promoting non-food use of agricultural resources and of reducing substantively production costs

Formulations used in a range of tests are shown in Table 2.

Quantities in g/batchFormulation A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12Potato Starch 52.5 52.5 52.5 52.5 52.5 52.5 52.5Wheat starch 52.5 52.5Potato mash 52.5 52.3

Guar gum 1 1 1 1 1 1 1 1 1 1 1 1Cellulose

fibers7.7 7.7 7.7 7.7 7.7 7.7 7.7 7.7 7.7 7.7 7.7 7.7

Wax 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5Magnesium

stereate2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3

Silane starch - 0.5 1. 1.5 2 2 2 2Polyvinyl alcohol

2 2 2 2

Alkylketene dimer

2 0 0

Table 2 Formulations of baked starch trays analysed during the project

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Trays obtained using the above formulations were analysed for stiffness. Strips were excised from the sample trays and then tested mechanically in an Instron Universal Testing Machine (16 experiments for each sample, data obtained is presented in Table 3, standard deviation varied for each sample 0.3–0.9 for MOE and 0.03–0.05 for MOR).

The contact angle was measured on a contact angle meter PGX Goniometer with water drops and a ratio between the measured contact angle and a contact angle of the same fluid in a steel surface was calculated and is indicated in the table.

MOE (N/mm2)

MOR(N/mm2)

Contact angle ratio

styrofoam 161 -----------A1 210 1.18 20A2 210 4.2 ----A3 207 4.56 78A4 208 4.89 84A5 210 5.36 95A6 416 2.88 35A7 236 2.02 48A8 190 3.8 90A9 398 5.12 35A10 412 5.12 96A11 198 4.88 92A12 405 2.69 39

Table 3 Mechanical and surface contact properties of produced baked trays

Generally, potato starch and potato mash provided better mechanical properties than wheat starch; however wheat starch (and possibly flour) can also be used to manufacture trays.

The results show that PVA increased the plasticity of the mixture, whilst silane starch increased substantially strength of the trays while inducing moisture resistance (entries A5, A8, A10, A12). AKD provide some intermediate properties.

Silane starches can provide highly hydrophobic trays (entries A5, A8, A10, A12), which additionally have high modulus, which suggest that despite higher density, trays with similar mechanical performances but similar weight with existing polystyrene trays could be obtained.1

Silane based trays were more dense. A possible explanation for the higher density of the silane starch trays may be related to the high viscosity of the correspondent batter which does not allow the growth of the steam water bubbles during the baking, causing it to be less expandable, giving rise to smaller average size, and thicker and stronger cell walls. The use of 1 Using the symbols wi –weight of material i, di-density of material i, ti-thickness of material i, Ei modulus of the material i, we can write, for the case of using silane starch (SiS) instead of polystyrene (PS) to produce trays with similar area for similar products that :C. WSiS = WPS Where c is a coeficient indicating the weight reduction C. Tpla .A. dpla = Tps .A. dppC.T SiS d SiS = T PS . d PS

C = T PS /T SiS d PS / d SiS

Assuming that the tray would behave like a beam, it could be deduced from the engineer bending equation, that the minimum thickness of trays is inversely proportional to the cubic root of the modulus, we can therefore write : C = (E SiS /E PS)0.33 d PS /d SiS

C = (4.3)0.33 * 0.73 = 1.18On the account of the errors in the assumptions, i.e. of the fact that the tray may not behave totally like a beam it is safe to consider that trays with the same weight and similar performance could be obtained with the two materials.

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baking powder to decrease the foams density of silane trays was observed, but formulations were not optimised.

To reduce the baking time, the potential of using microwave energy was also tested. Microwave is a very quick way to add heat, and is commonly used for heating foods, often containing starch. Microwave energy has also been used used to dissolve starch by heating and to prepare starch esters. It was expected to provide a very short and energy intense process for foaming starch. Preliminary experiments that were performed in a domestic microwave oven, using potato starch, baking powder and cellulosic fibres, showed that it is possible to produce foams within a very short time (less than 30 sec instead of the 5 minutes used at PotatoPak). Unfortunately all experiments provided foamed material with bits of chalky core that could not be eliminated in the experimental design.

At the time of making these experiments, the main shareholder of PotatoPak, Octel, decided to disinvest from the company, which in turn opted to seek alternative capital investment and at the same time halted its R&D programme, and so our experiments stopped at this stage.

Baking equipment and some formulation know-how, would however be available to interested operators based in the UK or in the EU, through PotatoPak, or PaperFoam (see www. Paperfoam.com) a company in the Netherlands selling trays for electronic packaging or from Franz Haas Waffel- und Keksanlagen-Industrie GmbH in Austria. Contact with one of the UK retailers with green credentials, Coop, indicated that they would be willing to buy non-GMO renewable based trays, produced in the UK with similar mechanical performance than existing materials, even if 15% more expensive than non-renewable based alternatives.

B3. Paint testing and drilling fluids

Polysaccharides have been used as rheological modifiers, and because silylated starch, with very low DS had high viscosity, it was a candidate as a new thickener additive in both interior and exterior paints. It was shown that electrolytes, pH, or ingredients such as dispersants, surfactants, and coalescents do not affect its performance, but comparison, perfomed by ICI Paints, with established hydroxyethylcellulose did not show any major technical advantage of the former product.

The industrial partner suggested that because product is heat resistant and behaves like hydroxyethylcellulose it could be used in the formulation of novel drilling muds. Drilling muds are used by the petroleum industry to seal well holes during drilling and should resist the high temperature found beneath the ground.

B4. Lightweight concrete

Lightweight concrete is important commercially because of its low sound and thermal conductivity. Glen and collaborators from the USDA have shown that composites of cement with a range of starch based gels could be used to make a very cheap light weight aggregate.22 The starch-based aggregate had however a lower compressive strength than commercial perlite concrete used in the UK.23 This was assumed to be due to a higher interfacial bonding that occurs between cement and perlite, but which is absent in starch based concrete. The purpose of the study was to explore whether a silylated starch can improve this interfacial bonding due to the existence of silicon both in cement and in modified starch. Testing proved that silane modified starches do not provide lightweight concrete with better mechanical properties (i.e. better Young’s modulus). Discussion with Glen from the USDA provided the following explanation. In the case of either modified or non-modified starch, wet starch dries inside the cement matrix, and therefore retracts, creating air pockets,

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which allow to have lightweight cement. In the case of perlite, the mineral is having air pockets naturally.

B5. Fire retardant improver

Fire retardants act by two general mechanisms, one is to create a barrier between the fire/fire source and the material to be protected, and the other is to interfere with the mechanism of combustion, slowing its inherent rate. The present fire retardant used to protect natural fibre insulants (e.g., flax) is sodium silicate. Adherence to the substrate is not perfect and, as a result, the fire retardancy properties of flax fibre insulation materials cannot match those of glass fibre competitiors. It is expected that silylated starch/ silylated starch with sodium silicate would provide a material with better adhesion.

Thermal analysis was chosen as a method to estimate the flame retardancy of a range of flax fibres treated with silane starche (trimethoxymethylsilane, sample TM), in concentrations of 15, 25 and 30 %, and trimethoxymethacrylate, sample TA) in concentration of 25%

Figure 7 Thermogravimetric analysis of silane starch coated fibres

The results are shown in Figure 7. In all the cases materials decomposed in two steps. The first is attributed to the initial decomposition of flax- similar to the one corresponding to cellulosic (untreated) fibres (550-650 K), while the second is due to the silane compounds. The residue at higher temperature is around 14%.

It was expected that the acrylate functional group (sample TA) would induce the formation of a protective char and would perform better than trimethoxymethylsilane modified starches, but this phenomenon could not be observed. However the data show categorically that the coating is a fire retardant which performance can potentially be improved by developing a formula with synergetic flame retardants.

PART C. General conclusions: Implications of the results and possible future work.

The first objective of the project, the development of an environmentally friendly procedure to obtain starch silane derivatives has been met. The potential of using such procedures in modifying other polysaccharides need also to be investigated in future work.

The second project objective, an analyse of potential industrial uses of the obtained material, as additive for the paper coating, baked starch trays manufacture, fire retardant improver, in light cement composites manufacturing and as a paint additive has also been investigated.

It has been shown that in the first two cases, silane starch can induce hydrophobicity to the materials. Additionally, it has been shown that baked starch trays can have higher modulus,

SID 5 (Rev. 3/06) Page 14 of 16

with the potential for production cost reductions, as the amount of starch per tray can be significantly reduced.

Despite the fact that the main UK operator developing starch baked technology is not at the moment of writing this report involved in major production effort or in R&D, the equipment and start-up technology for other interested companies is available in the market.

On the basis that wheat and mashed potato can be used in foam tray manufacture and the fact that the K is both a major wheat and potato producer, the potential direct use of potato and wheat should be investigated looking not only to develop the technology analysed during the present research, but also to other processing technologies, like foam extrusion, which have shorter cycle times, and would potentially be more competitive.

Potential use of starch silane as a fire retardant additive in the formulation of natural fibers insulations has been demonstrated, however formulations still need to be developed.

The use of starch silane in lightweight cements in the limits of the study has been shown to be inappropriate with no performance gains achieved.

The potential use os silane starches as thixotropic agents did not show competitive advantage over established products, except with the fact that silane starch products have high temperature resistance. This suggest their potential use as novel drilling mud additives. Such analysis is to be performed by Stadex, the industrial partner in the project.

A major potential new end-use, not foreseen when the project proposal was initially discussed is the potential use in the cheaper manufacture of the so-called “Green Tyre”. This has been introduced recently as a new type of tyre which allow cars to consume less energy because they produce less attrition for a given distance to be covered. These are produced using starch silane sulfur additives which are obtained in rubber extrusion equipment using very high mechanical energy to bind starch to the silane-sulfur. The additive may be used late in the formulation to afford a blend to manufacture the tyre. This is only hypothesis and no trials have been made but we believe there is the potential to use chemistry developed in this project to improve the manufacture and performance of the green tyre.

The fact that we can bind starch to silane at room temperature, using catalysts, suggests that the energy for the first step could be drastically reduced, reducing costs and improving overall gas emissions during the lifetime of the project.

Preliminary experiments, self-funded by the BioComposites Centre, Bangor and IPTME Loughborough, are currently underway to prove the validity of the new concept, and also allow its use in other applications of rubber based products in the transport sector, from tank pads to rubber belts.

References to published material9. This section should be used to record links (hypertext links where possible) or references to other

published material generated by, or relating to this project.

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1- www.ics.trieste.it/documents/chemistry/plastics/ activities/egm-Sept2002/DegliInnocenti.pdf –accessed on 10 June 2005.

2- Zollfrank, Wood Sci Technol ,35,2001, 183-189.

3-Mormann, W., Demeter, J., Macromolecules, 1999, 32, 1706-1710.

4.Petzold, K., Koshella, A., Klemm,D., Heublein,B., Cellulose, 2003, 10, 251-269.

5.Blackwell, JM, J.Org.Chem., 1999, 64, 4887-4892.

6.Clive, D., Tetrahedron Letters, 1991, 64, 4887-4892.

7.Arkles, B.,Chem.Tech., 1977, 7, 766-778.

8.Bletzki, AK, Gassan, J., Prog.Polym.Sci., 1999, 24, 221-274.

9.Donatz, S., Millitz, H., Mai, C., Wood Sci. Technol., 2004, 38, 555-566.

10.Sebe, G., Tingaut, P., Safout, R., Petraud, M., De Jeso, B., Holzforshung, 2004, 58, 511-518.

11.WO99/21892

12.Castellano, M., Gandini, A., Fabbri, P., Belgacem, M.N., J.Colloid and Interface Sci., 2004, 273, 505-511.

13.Epping, J.D. / Chmelka, B.F., Current Opinion in Colloid & Interface Science, 2006, 11, 81-117.

13.Pickering, KL, Abdalla, A., Ji, C., McDonald, AG, Franich, RA, Composites Part A, 2003, 34, 915-926

14.Entwistle, G., Bachelor, S., Booth, E.,Walker, K., Industrial Crops and Products, 1998, 7, 175-186.

15.Gill, R.I.S., Paper Technology, 1991, 32, 34-41.

16.http://www.earthshell.com. last accessed on 23 June 2006

17.Andersen J., Hodson S., WO 9612606

18.Meeuwsen,M.C., “Method of producing a biodegradable product”, US patent 6,461, 549, attributed to PotatoPak Limited GB.

19. Lawton, Shogren, Tiefenbacher, Cereal Chem., 1999, 76, 682-687.

20.Glen, GM, Miller, RM, Orts, WJ, Industrial Crops and Products, 1998, 8, 123, 132.

21.Neville, A.M., Properties of Concrete, 4th Ed. Longman, Harlow, England, 426-436.

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