Duono de la teksaĵo estas silko.

Because duono is a noun meaning half or one half.

In this sentence, duono is the main word of the subject:

Duono de la teksaĵo = half of the textile/fabric

By contrast, duona is an adjective meaning half- or partial, and it has to modify another noun:

• duona horo = half an hour
• duona pano = half a loaf

So here, duono is correct because we are naming a thing: a half.

It means of the textile/fabric.

Esperanto commonly uses de to show the whole that a fraction belongs to:

• duono de la kuko = half of the cake
• triono de la klaso = a third of the class
• parto de la mono = part of the money

So duono de la teksaĵo literally means half of the textile/fabric.

Because la shows that we are talking about a specific textile/fabric, not fabric in general.

So:

• la teksaĵo = the textile/fabric, the one already known in context
• teksaĵo = textile/fabric in a general or indefinite sense

In a sentence like this, la usually means the speaker and listener both know which material is being discussed.

Teksaĵo comes from:

• teks- = weave
• -aĵ- = a concrete thing or product
• -o = noun ending

So teksaĵo means something like a woven thing, textile, or fabric.

Depending on context, an English translation might be:

• textile
• fabric
• woven material
• cloth

The exact best translation depends on what kind of material is being discussed.

Because silko is a noun meaning silk, and here it is being used after estas to identify the material.

So:

• estas silko = is silk
• estas silka = is silk / is made of silk, using an adjective

Both noun and adjective patterns can exist in Esperanto, but the noun is very natural when naming the material itself.

Compare:

• Tio estas oro. = That is gold.
• La ringo estas ora. = The ring is golden / made of gold.

In your sentence, silko straightforwardly names the substance.

Because silko here means the material silk in general, not the silk as a specific previously mentioned piece or amount.

After estas, Esperanto often leaves out la when giving a category or material:

• Ĝi estas akvo. = It is water.
• Tio estas ligno. = That is wood.
• Duono de la teksaĵo estas silko. = Half of the fabric is silk.

If you said la silko, it would sound like the silk, meaning some particular silk already known from context.

No. The subject is only duono de la teksaĵo — half of the fabric.

So the sentence says that that half is silk. It leaves open what the other half is. For example, the other half might be cotton, wool, or something else.

Yes, you could, but the nuance is a little different.

• Duono de la teksaĵo = half of the fabric
• La duono de la teksaĵo = the half of the fabric

Without la, it sounds more like a quantity statement. With la, it can sound more definite, as if that particular half is being identified.

In many contexts, both are possible, but duono de... is very common for simple fraction statements.

Because there is no direct object here.

The structure is:

• Duono de la teksaĵo = subject
• estas = verb
• silko = predicate noun / complement

After esti, the complement does not take -n.

Compare:

• Tio estas libro. = That is a book.
• Li estas instruisto. = He is a teacher.

Also, de la teksaĵo is a prepositional phrase, and prepositions normally do not use accusative for direct-object purposes.

With fractions, de is the normal choice:

• duono de la pomo = half of the apple
• kvarono de la urbo = a quarter of the city

El often means out of or from among, especially with counted items:

• du el la kvin studentoj = two out of the five students

So for a fraction of a thing or substance, de is the usual and expected preposition here.

Normally, yes. Duono means one of two equal parts.

If you want to be especially clear, you could say:

• ĝuste duono = exactly half

If you mean something less exact, Esperanto would usually use a different expression, such as:

• preskaŭ duono = almost half
• ĉirkaŭ duono = about half
• parto de = part of

So by default, duono suggests a real half, not just a large part.