Ĉi tiu firmao recikligas plaston.

Because plaston is the direct object of the verb recikligas.

In Esperanto, nouns take -n when they are the thing directly affected by the action:

• La firmao recikligas plaston. = The company recycles plastic.
• Mi vidas la domon. = I see the house.

Here, the company is doing the recycling, and plastic is what gets recycled, so plasto becomes plaston.

This -n ending is called the accusative ending.

Both are possible, but they mean slightly different things.

• plaston = plastic in a general sense
• la plaston = the plastic, some specific plastic already known from context

So:

• Ĉi tiu firmao recikligas plaston. = This company recycles plastic.
• Ĉi tiu firmao recikligas la plaston. = This company recycles the plastic.

In your sentence, plaston is used generically, which is very natural.

Ĉi tiu means this.

It is made of:

• tiu = that
• ĉi = a particle that brings the meaning closer, like here / this one

So:

• tiu firmao = that company
• ĉi tiu firmao = this company

You can think of ĉi as turning that into this.

Esperanto also sometimes allows tiu ĉi, and it means the same thing:

• ĉi tiu firmao
• tiu ĉi firmao

Both mean this company.

Because -as is the present-tense verb ending in Esperanto.

Verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / wish
• -i = infinitive

So:

• recikligi = to recycle
• recikligas = recycles / is recycling
• recikligis = recycled
• recikligos = will recycle

In Esperanto, verbs do not change according to the subject:

• mi recikligas
• vi recikligas
• li recikligas
• ili recikligas

The form stays the same.

Yes. Firmao means company, firm, or business.

It is a noun, and nouns in Esperanto normally end in -o:

• firmao = company
• domo = house
• libro = book

If you want the plural:

• firmaoj = companies

And if it is a direct object:

• firmaon

A rough English-friendly pronunciation is:

chee TEE-oo feer-MAH-oh re-tsi-KLEE-gahs PLAH-ston

A few helpful points:

• ĉ sounds like ch in church
• tiu is roughly TEE-oo
• c in Esperanto sounds like ts
• g is always a hard g, as in go
• stress is normally on the second-to-last syllable

So:

• ĈI tiu? No — stress is actually on TI in tiu, because it has two syllables: TI-u
• fir-MA-o
• re-ci-KLI-gas
• PLAS-ton

Yes, Esperanto word order is fairly flexible, mainly because the -n ending helps show what is the object.

The neutral order is:

• Ĉi tiu firmao recikligas plaston.

But you could also say:

• Plaston recikligas ĉi tiu firmao.

That still means This company recycles plastic, because plaston has -n, so it is clearly the object.

Even so, the original order is the most straightforward and natural for most situations.

Because Esperanto usually expresses tense directly in the main verb, without needing an extra helping verb like English often does.

English says:

• This company recycles plastic.
• This company is recycling plastic.

Esperanto can often use the same present-tense form:

• Ĉi tiu firmao recikligas plaston.

So recikligas already carries the idea of a present action or habitual action. There is no need for a separate word meaning does or is here.

Yes. Esperanto often builds words from meaningful parts.

recikligi can be understood as related to ciklo (cycle) and the idea of doing something again or in a circular process. In practice, you should simply learn recikligi as to recycle, but it also fits Esperanto’s very productive word-building system.

Once you know the root, you can make related forms:

• recikligi = to recycle
• recikligo = recycling
• recikligebla = recyclable
• recikligita = recycled

This is one of the useful things about Esperanto: vocabulary often works in a very systematic way.

Because plaston here means plastic as a material or substance in general, not multiple separate plastics.

If you were talking about different kinds of plastics or individual plastic items, you might use a plural form in another context, but in this sentence the singular is the natural choice.

Compare:

• plasto = plastic as a material
• plastoj = plastics, kinds of plastic, or plastic items depending on context

So plaston is singular direct object: plastic.

Yes, but the meaning changes.

• Ĉi tiu firmao recikligas plaston. = This company recycles plastic.
• Tiu firmao recikligas plaston. = That company recycles plastic.

So if you want to point to something near you, or something you are focusing on as this one, use ĉi tiu. If you mean that one, use tiu alone.